Levels vs Curves?

In article <p2ole.20890$>,
"KatWoman" wrote:

To correct exposures I find it easier to use levels. Assuming I don’t move the far left and right points (which I have been told "clips" info out of your document) is there any reason why using curves is superior?

Moving the far left and right points only clips image detail if you move them in past the beginning or end of the histogram.

If you have an image whose histogram is, say, all on the left-hand side–there are no pixels on the right-hand side, meaning there are no hilight pixels–then moving the right-hand end point to the beginning of the histogram does not clip detail.

When you move the center triangle, what you are doing is identical to clicking on the very center in the Curves command and moving it up or down. The Curves command allows oyu to do far more, however. It allows you, for example, to increase or decrease contrast, to lighten only the shadows without affecting the hilights, to lighten only the midtones without affecting the hilights or shadows, to increase contrast only in hilights, and so on, and so on. None of these can be done with Levels.

—
Art, photography, shareware, polyamory, literature, kink: all at http://www.xeromag.com/franklin.html

On 5/26/05 1:18 PM, tacit uttered:

In article <p2ole.20890$>,
"KatWoman" wrote:

To correct exposures I find it easier to use levels. Assuming I don’t move the far left and right points (which I have been told "clips" info out of your document) is there any reason why using curves is superior?

Moving the far left and right points only clips image detail if you move them in past the beginning or end of the histogram.

If you have an image whose histogram is, say, all on the left-hand side–there are no pixels on the right-hand side, meaning there are no hilight pixels–then moving the right-hand end point to the beginning of the histogram does not clip detail.

When you move the center triangle, what you are doing is identical to clicking on the very center in the Curves command and moving it up or down. The Curves command allows oyu to do far more, however. It allows you, for example, to increase or decrease contrast, to lighten only the shadows without affecting the hilights, to lighten only the midtones without affecting the hilights or shadows, to increase contrast only in hilights, and so on, and so on. None of these can be done with Levels.

I’ve used photoshop for years, but for the life of me, I find Curves the completely unusable. I use a combination of Level, Hue/Saturation, Color Balance and so on. Anything but Curves. I find Curves one of the least intuitive tools I’ve ever attempted to use, and the least little move makes too much difference. It’s true, though, that I gave up trying to practice with it long ago, but I found it just too frustrating.

inez

KatWoman writes …

Does it matter which type of adjustment?
To correct exposures I find it easier to use levels.

Levels lets you move three points, the two ends and the middle. If that’s all you need, it’s fine, especially since you see the histogram, which makes it easier to set end points without clipping.

Curves lets you move any of 256 points so it’s much more flexible, especially in the quarter and three quarter tonal areas which you can’t reach directly with Levels. One thing you can do easily with Curves but you can’t do with Levels, for example, is apply an S-curve to increase contrast (or reverse S to decrease contrast). I also find it easier to remove a color cast with Curves than with the other tools since it’s easy to click on a spot to set a point on the curve and then modify it with the arrow keys.

Curves is not as intuitive but I personally think it’s well worth the effort to learn how to use it. Many scanning programs have Curves superimposed over a histogram, often with the equivalent of Levels at the bottom of the screen, so you can make an adjustment with either tool and see it in the histogram. I wish Photoshop did this (at least the histogram part), it would make using Curves more intuitive.

Bill

iehsmith wrote:
….

I’ve used photoshop for years, but for the life of me, I find Curves the completely unusable. I use a combination of Level,
Hue/Saturation, Color Balance and so on. Anything but Curves. I find Curves one of the least intuitive tools I’ve ever attempted to use, and the least little move makes too much difference. It’s true, though, that I gave up trying to practice with it long ago, but I found it just too frustrating.

Now that you’re comfortable with Levels, it may be time to give Curves another try. I was happy with Levels for years – after all it is much more effective that anything you can do in the darkroom. Taking a wrong turn with curves is like driving a car in the dark with the headlights off.

I did not really use curves seriously until I read my first book by Dan Margulis – talk about an eye opener! As I look back on my own prints, it’s obvious where I stopped using levels and switched to curves. —

Mike Russell
www.curvemeister.com

On 5/26/05 3:41 PM, Mike Russell uttered:

Taking a wrong turn with curves is like driving a car in the dark with the headlights off.

Yes, that’s the problem I consistently had with it. And it seems the least nudge is a move too much.

I did not really use curves seriously until I read my first book by Dan Margulis – talk about an eye opener! As I look back on my own prints, it’s obvious where I stopped using levels and switched to curves.

Perhaps it will take a book to cure me;)

inez

"Bill Hilton" wrote in message
SNIP

Many scanning programs have Curves superimposed over
a histogram, often with the equivalent of Levels at the
bottom of the screen, so you can make an adjustment with either tool and see it in the histogram. I wish Photoshop did this (at least the histogram part), it would make using Curves more intuitive.

In a way (in a seperate display), Photoshop CS and CS2 do just that with the life update of the histogram which, unlike the Levels histogram that only shows R+G+B quantities per level, allows a multitude of histogram representations (amongst others luminocity which is closer to our perception of brightness levels).

Bart

On Thu, 26 May 2005 14:00:05 -0400, "KatWoman" wrote:

Does it matter which type of adjustment?

To correct exposures I find it easier to use levels. Assuming I don’t move the far left and right points (which I have been told "clips" info out of your document) is there any reason why using curves is superior? Also I always use this on an adjustment layer so if it’s not "correct" it can be changed. I like seeing the histogram when making adjustments. I used to like using the curve palette in my scanner software but the PS one doesn’t work similarly, it tends to make little bumpy mountains instead of a smooth overall curve, perhaps I am not using the tool well.

You’re limited to three points in levels. You have 256 points to play with in curves. I know it’s Photoshop, but a good way of seeing why this is important is to read Dan Margulis’ Professional Photoshop.

—

Hecate – The Real One

Fashion: Buying things you don’t need, with money
you don’t have, to impress people you don’t like…

Thanks, I just tried using the curves and did get much better results in overall color than with levels.
I wasn’t using the tool correctly, it wasn’t bending where I wanted but now I get it.

"tacit" wrote in message

In article <p2ole.20890$>,
"KatWoman" wrote:

To correct exposures I find it easier to use levels. Assuming I don’t move
the far left and right points (which I have been told "clips" info out of your document) is there any reason why using curves is superior?

Moving the far left and right points only clips image detail if you move them in past the beginning or end of the histogram.

If you have an image whose histogram is, say, all on the left-hand side–there are no pixels on the right-hand side, meaning there are no hilight pixels–then moving the right-hand end point to the beginning of the histogram does not clip detail.

When you move the center triangle, what you are doing is identical to clicking on the very center in the Curves command and moving it up or down. The Curves command allows oyu to do far more, however. It allows you, for example, to increase or decrease contrast, to lighten only the shadows without affecting the hilights, to lighten only the midtones without affecting the hilights or shadows, to increase contrast only in hilights, and so on, and so on. None of these can be done with Levels.
—
Art, photography, shareware, polyamory, literature, kink: all at http://www.xeromag.com/franklin.html

In article <BEBB978B.3378D%>,
iehsmith wrote:

I’ve used photoshop for years, but for the life of me, I find Curves the completely unusable. I use a combination of Level, Hue/Saturation, Color Balance and so on.

Color Balance is actually not a good tool to use; Color Balance and Brightness/Contrast both degrade the quality of the image by clipping hilight and/or shadow detail.

Anything but Curves. I find Curves one of the least
intuitive tools I’ve ever attempted to use, and the least little move makes too much difference. It’s true, though, that I gave up trying to practice with it long ago, but I found it just too frustrating.

Really? Curves allows incredibly subtle image manipulation. Anything you can do with Brightness/Contrast, Color Balance, and so on, you can do with Curves–but without degrading the image the way Brightness/Contrast and Color Balance do.

—
Art, photography, shareware, polyamory, literature, kink: all at http://www.xeromag.com/franklin.html

iehsmith wrote:

I’ve used photoshop for years, but for the life of me, I find Curves the completely unusable. I use a combination of Level,
Hue/Saturation, Color Balance and so on.

I have a feeling you’re on the verge of trying out curves again. You might find this article interesting:

http://www.curvemeister.com/support/curvemeister2/help/Artic les/WhyCurves.htm —
Mike Russell
www.curvemeister.com

KatWoman wrote:

Does it matter which type of adjustment?

To correct exposures I find it easier to use levels. Assuming I don’t move the far left and right points (which I have been told "clips" info out of your document) is there any reason why using curves is superior? Also I always use this on an adjustment layer so if it’s not "correct" it can be changed. I like seeing the histogram when making adjustments. I used to like using the curve palette in my scanner software but the PS one doesn’t work similarly, it tends to make little bumpy mountains instead of a smooth overall curve, perhaps I am not using the tool well.

Bill has already provided an excellent explanation between levels and curves. Jay Arraich went one step further with his detailed article here, although its demonstration is based only on a single b/w image.

http://www.arraich.com/ps6_tips_ccontrast1.htm

Like Mike and others, I cut my teeth on curves after reading Margulis (caution: NOT for beginners, VERY opinionated, click by click tutorials are NON-existent, you better LIKE his writing style, etc.). His theories are excellent and made me a convert, even though I still don’t understand everything he says. For a period, I tried to rely only on curves for all my corrections. While curves are as powerful as others mentioned, I also find problems with them, such as:

– It is tedious to use curves well. For critical corrections (and if not critical, why bother with curves to begin with?), I have to know which channel to move, where on each channel to move, how much to move, how many channels to move, etc. When a correction requires multiple point moves, your curves window can stay open for quite a while. And that’s assuming that you have analyzed the problem correctly BEFORE moving curves, and that you DON’T change your mind later. Unwinding all (or some of) your curve corrections and starting over again is a REAL drag. Pardon the pun.

– While curves let you increase contrast for one part of the image, it is at the expense of decreasing contrast somewhere else. Sometimes the tradeoff is not easy or desirable.

– Correcting for contrast with curves may screw up the colors, and vice versa.

– As Margulis points out, sometimes correcting with curves within a single color space just won’t do the trick. Borrowing and blending channels from other color spaces is the solution. To do that, you better be able to walk on water.

– The power of curves can result in excessive data destruction (8 or 16 bits), and unnatural looking images. OK, same holds true for other tools.

(Now, why don’t $50 books tell you these things?)

I still use curves, but now also rely on other tools such as Selective Colors (which I don’t think curves can do). Jay Arraich goes as far as calling curves "abominable":

http://www.arraich.com/ps8_CurvesCommentary1.htm

KatWoman wrote:

Does it matter which type of adjustment?

To correct exposures I find it easier to use levels. Assuming I don’t move the far left and right points (which I have been told "clips" info out of your document) is there any reason why using curves is superior? Also I always use this on an adjustment layer so if it’s not "correct" it can be changed. I like seeing the histogram when making adjustments. I used to like using the curve palette in my scanner software but the PS one doesn’t work similarly, it tends to make little bumpy mountains instead of a smooth overall curve, perhaps I am not using the tool well.

Bill has already provided an excellent explanation between levels and curves. Jay Arraich went one step further with his detailed article here, although its demonstration is based only on a single b/w image.

http://www.arraich.com/ps6_tips_ccontrast1.htm

Like Mike and others, I cut my teeth on curves after reading Margulis (caution: NOT for beginners, VERY opinionated, click by click tutorials are NON-existent, you better LIKE his writing style, etc.). His theories are excellent and made me a convert, even though I still don’t understand everything he says. For a period, I tried to rely only on curves for all my corrections. While curves are as powerful as others mentioned, I also find problems with them, such as:

– It is tedious to use curves well. For critical corrections (and if not critical, why bother with curves to begin with?), I have to know which channel to move, where on each channel to move, how much to move, how many channels to move, etc. When a correction requires multiple point moves, your curves window can stay open for quite a while. And that’s assuming that you have analyzed the problem correctly BEFORE moving curves, and that you DON’T change your mind later. Unwinding all (or some of) your curve corrections and starting over again is a REAL drag. Pardon the pun.

– While curves let you increase contrast for one part of the image, it is at the expense of decreasing contrast somewhere else. Sometimes the tradeoff is not easy or desirable.

– Correcting for contrast with curves may screw up the colors, and vice versa.

– As Margulis points out, sometimes correcting with curves within a single color space just won’t do the trick. Borrowing and blending channels from other color spaces is the solution. To do that, you better be able to walk on water.

– The power of curves can result in excessive data destruction (8 or 16 bits), and unnatural looking images. OK, same holds true for other tools.

(Now, why don’t $50 books tell you these things?)

I still use curves, but now also rely on other tools such as Selective Colors (which I don’t think curves can do). Jay Arraich goes as far as calling curves "abominable":

http://www.arraich.com/ps8_CurvesCommentary1.htm

In article , says…

I still use curves, but now also rely on other tools such as Selective Colors (which I don’t think curves can do). Jay Arraich goes as far as calling curves "abominable":

http://www.arraich.com/ps8_CurvesCommentary1.htm

This commentary is just foolish. In conventional photography there is a "curve" applied by the response of the film to light. There is another "curve" applied by the type and degree of developing and yet others for the print and print developing.
Even viewing on a screen applies a curve.
The eye’s response to light is logarithmic: a curve.
Digital cameras have linear response to light, but this produces an unnatural effect so the image is processed through a curve. Proper application of curves is much more powerful that levels. And everything you do with levels can be done with an equivalent curve. The only feature missing from the curves dialog is the ability to preview the clipping by pressing ALT while moving the levels end points. Even in this case it is possible to note the values and transfer them to a curve after dismissing the levels dialog.
More in the tips section of my web site.

—
Robert D Feinman
Landscapes, Cityscapes and Panoramic Photographs
http://robertdfeinman.com
mail:

In article , says…

I still use curves, but now also rely on other tools such as Selective Colors (which I don’t think curves can do). Jay Arraich goes as far as calling curves "abominable":

http://www.arraich.com/ps8_CurvesCommentary1.htm

This commentary is just foolish. In conventional photography there is a "curve" applied by the response of the film to light. There is another "curve" applied by the type and degree of developing and yet others for the print and print developing.
Even viewing on a screen applies a curve.
The eye’s response to light is logarithmic: a curve.
Digital cameras have linear response to light, but this produces an unnatural effect so the image is processed through a curve. Proper application of curves is much more powerful that levels. And everything you do with levels can be done with an equivalent curve. The only feature missing from the curves dialog is the ability to preview the clipping by pressing ALT while moving the levels end points. Even in this case it is possible to note the values and transfer them to a curve after dismissing the levels dialog.
More in the tips section of my web site.

—
Robert D Feinman
Landscapes, Cityscapes and Panoramic Photographs
http://robertdfeinman.com
mail:

wrote:

KatWoman wrote:

Does it matter which type of adjustment?

To correct exposures I find it easier to use levels. Assuming I don’t move the far left and right points (which I have been told "clips" info out of your document) is there any reason why using curves is superior?
Also I always use this on an adjustment layer so if it’s not "correct" it can be changed. I like seeing the histogram when making adjustments.
I used to like using the curve palette in my scanner software but the PS one doesn’t work similarly, it tends to make little bumpy mountains instead of a smooth overall curve, perhaps I am not using the tool well.

Bill has already provided an excellent explanation between levels and curves. Jay Arraich went one step further with his detailed article here, although its demonstration is based only on a single b/w image.
http://www.arraich.com/ps6_tips_ccontrast1.htm

Like Mike and others, I cut my teeth on curves after reading Margulis (caution: NOT for beginners, VERY opinionated, click by click tutorials
are NON-existent, you better LIKE his writing style, etc.). His theories
are excellent and made me a convert, even though I still don’t understand everything he says. For a period, I tried to rely only on curves for all my corrections. While curves are as powerful as others mentioned, I also find problems with them, such as:

– It is tedious to use curves well. For critical corrections (and if not critical, why bother with curves to begin with?), I have to know which channel to move, where on each channel to move, how much to move, how many channels to move, etc.

I don’t agree that curves are tedious. I think they are fun and I have managed to convince others of this countless times in my class. I think you’re overstating the complexity, and not really describing how curves are normally used. Much of the changing and rearrangement of curves is experimental in nature. It is a process of feedback and compromise based on how the image looks, and how the numeric color values change. For example, I will often try using an S curve and an inverted S on an image to see which looks best.

When a correction requires multiple point
moves, your curves window can stay open for quite a while. And that’s assuming that you have analyzed the problem correctly BEFORE moving curves, and that you DON’T change your mind later. Unwinding all (or some of) your curve corrections and starting over again is a REAL drag. Pardon the pun.

But these objections are the same for any color correction method, whether it involves curves or not. Although it helps, there is no need to predict anything before using curves, and Photoshop’s history mechanism makes undoing of previous curve operations simple. Starting over again is as simple as ctrl-Z, and you may use history, adjustment layers or re-load a curve file if you want to modify your previous curves.

– While curves let you increase contrast for one part of the image, it is at the expense of decreasing contrast somewhere else. Sometimes the tradeoff is not easy or desirable.

But the whole goal of using curves is to perform exactly this kind of trade-off: adding color and contrast to some areas of an image, while taking it away from others.

– Correcting for contrast with curves may screw up the colors, and vice versa.

This is a true, and often ignored, fact about the RGB and CMYK master curves – they can cause unwanted changes to color hues, and should not really be used. Lab avoids this problem by separating color and brightness information into the Lightness and the a and b channels. Since changing color is generally more subtle than changing contrast, as a practical matter the "vice-versa" portion of your statement is not a concern.

– As Margulis points out, sometimes correcting with curves within a single color space just won’t do the trick. Borrowing and blending channels from other color spaces is the solution. To do that, you better be able to walk on water.

One common way to blend channel data is by use of Selective Color. I do this all the time and it can often fix an image in a matter of seconds. And your feet will stay dry.

– The power of curves can result in excessive data destruction (8 or 16 bits), and unnatural looking images. OK, same holds true for other tools.

I think you’ve answered your own question in that any image modificationk, by its nature, changes data values. I would add that data is not destroyed by moving it around. If a steeper curve makes the image look better, so be it.

(Now, why don’t $50 books tell you these things?)

Good point. That’s why we have Usenet. 🙂

I still use curves, but now also rely on other tools such as Selective Colors (which I don’t think curves can do).

Lab comes close, however I would be the last person to say curves are the only tool available.

Jay Arraich goes as far as
calling curves "abominable":

http://www.arraich.com/ps8_CurvesCommentary1.htm

Fun article – I’m always ready to enjoy a little icono-clasm :-)> But it is inaccurate in several respects, not the least of which is the fact that Ansel Adams did not rely just on dodging and burning, but spent much time and effort manipulating the characteristic curve of both film and print by modifying developer chemistry. In fact, changing paper grades is very much like using Levels or Contrast – altering developing techniques, as Adams did, foreshadowed Curves.
—
Mike Russell
www.curvemeister.com

wrote:

KatWoman wrote:

Does it matter which type of adjustment?

To correct exposures I find it easier to use levels. Assuming I don’t move the far left and right points (which I have been told "clips" info out of your document) is there any reason why using curves is superior?
Also I always use this on an adjustment layer so if it’s not "correct" it can be changed. I like seeing the histogram when making adjustments.
I used to like using the curve palette in my scanner software but the PS one doesn’t work similarly, it tends to make little bumpy mountains instead of a smooth overall curve, perhaps I am not using the tool well.

Bill has already provided an excellent explanation between levels and curves. Jay Arraich went one step further with his detailed article here, although its demonstration is based only on a single b/w image.
http://www.arraich.com/ps6_tips_ccontrast1.htm

Like Mike and others, I cut my teeth on curves after reading Margulis (caution: NOT for beginners, VERY opinionated, click by click tutorials
are NON-existent, you better LIKE his writing style, etc.). His theories
are excellent and made me a convert, even though I still don’t understand everything he says. For a period, I tried to rely only on curves for all my corrections. While curves are as powerful as others mentioned, I also find problems with them, such as:

– It is tedious to use curves well. For critical corrections (and if not critical, why bother with curves to begin with?), I have to know which channel to move, where on each channel to move, how much to move, how many channels to move, etc.

I don’t agree that curves are tedious. I think they are fun and I have managed to convince others of this countless times in my class. I think you’re overstating the complexity, and not really describing how curves are normally used. Much of the changing and rearrangement of curves is experimental in nature. It is a process of feedback and compromise based on how the image looks, and how the numeric color values change. For example, I will often try using an S curve and an inverted S on an image to see which looks best.

When a correction requires multiple point
moves, your curves window can stay open for quite a while. And that’s assuming that you have analyzed the problem correctly BEFORE moving curves, and that you DON’T change your mind later. Unwinding all (or some of) your curve corrections and starting over again is a REAL drag. Pardon the pun.

But these objections are the same for any color correction method, whether it involves curves or not. Although it helps, there is no need to predict anything before using curves, and Photoshop’s history mechanism makes undoing of previous curve operations simple. Starting over again is as simple as ctrl-Z, and you may use history, adjustment layers or re-load a curve file if you want to modify your previous curves.

– While curves let you increase contrast for one part of the image, it is at the expense of decreasing contrast somewhere else. Sometimes the tradeoff is not easy or desirable.

But the whole goal of using curves is to perform exactly this kind of trade-off: adding color and contrast to some areas of an image, while taking it away from others.

– Correcting for contrast with curves may screw up the colors, and vice versa.

This is a true, and often ignored, fact about the RGB and CMYK master curves – they can cause unwanted changes to color hues, and should not really be used. Lab avoids this problem by separating color and brightness information into the Lightness and the a and b channels. Since changing color is generally more subtle than changing contrast, as a practical matter the "vice-versa" portion of your statement is not a concern.

– As Margulis points out, sometimes correcting with curves within a single color space just won’t do the trick. Borrowing and blending channels from other color spaces is the solution. To do that, you better be able to walk on water.

One common way to blend channel data is by use of Selective Color. I do this all the time and it can often fix an image in a matter of seconds. And your feet will stay dry.

– The power of curves can result in excessive data destruction (8 or 16 bits), and unnatural looking images. OK, same holds true for other tools.

I think you’ve answered your own question in that any image modificationk, by its nature, changes data values. I would add that data is not destroyed by moving it around. If a steeper curve makes the image look better, so be it.

(Now, why don’t $50 books tell you these things?)

Good point. That’s why we have Usenet. 🙂

I still use curves, but now also rely on other tools such as Selective Colors (which I don’t think curves can do).

Lab comes close, however I would be the last person to say curves are the only tool available.

Jay Arraich goes as far as
calling curves "abominable":

http://www.arraich.com/ps8_CurvesCommentary1.htm

Fun article – I’m always ready to enjoy a little icono-clasm :-)> But it is inaccurate in several respects, not the least of which is the fact that Ansel Adams did not rely just on dodging and burning, but spent much time and effort manipulating the characteristic curve of both film and print by modifying developer chemistry. In fact, changing paper grades is very much like using Levels or Contrast – altering developing techniques, as Adams did, foreshadowed Curves.
—
Mike Russell
www.curvemeister.com

Thank you all for the in-depth replies. I used to always use curves in my scanner software and after comparison of levels vs. curves in a particular underexposed frame, I find the curve adjustment to be far superior. As I usually like to pull more from the shadow and less from the highlight, pulling the curve at a point above the center is better for me. Of course it would be great to have a perfect in-camera exposure, but here in sunny Florida the big puffy clouds going overhead caused a great variety of exposures (similar to bracketing) and wouldn’t you know it the client liked one of the dark frames best. (We did try and pause for the clouds but still snapped off a few frames before waiting for them to pass.) I have also used selective color to further adjust the magenta sweater she wore as it comes out reddish on digital. Even with film I find purple and magenta often don’t register enough blue and look reddish instead of pinkish.

I am also experimenting with a new sharpen technique I saw on the NG but have modified to my own technique.
I am making a dupe layer of my orig, put it under orig layer, oversharpen the under layer with unsharp mask, put original on top on COLOR blending mode, then erase original on the skin only, keeping it softer focus and allowing the sharpening to show through the rest. So now everything is sharper except on the skin where I don’t want it sharp. I tried using the high pass filter as the under layer but wasn’t happy with my results. And yes I do see that curves can make your whole image look crazy colors, in fact I have used this technique to make some wild looking images. Now I will use curves to make corrections as well.

Now I tried the little pencil thing in the tool and it makes breaks in the curve line but I am not sure how or when I would use that. Thankfully my photographer gives me properly exposed and focused originals most of the time.

"Mike Russell" wrote in message

wrote:

KatWoman wrote:

Does it matter which type of adjustment?

To correct exposures I find it easier to use levels. Assuming I don’t move the far left and right points (which I have been told "clips" info out of your document) is there any reason why using curves is superior?
Also I always use this on an adjustment layer so if it’s not "correct" it can be changed. I like seeing the histogram when making adjustments.
I used to like using the curve palette in my scanner software but the PS one doesn’t work similarly, it tends to make little bumpy mountains instead of a smooth overall curve, perhaps I am not using the tool well.

Bill has already provided an excellent explanation between levels and curves. Jay Arraich went one step further with his detailed article here, although its demonstration is based only on a single b/w image.
http://www.arraich.com/ps6_tips_ccontrast1.htm

Like Mike and others, I cut my teeth on curves after reading Margulis (caution: NOT for beginners, VERY opinionated, click by click tutorials
are NON-existent, you better LIKE his writing style, etc.). His theories
are excellent and made me a convert, even though I still don’t understand everything he says. For a period, I tried to rely only on curves for all my corrections. While curves are as powerful as others mentioned, I also find problems with them, such as:

– It is tedious to use curves well. For critical corrections (and if not critical, why bother with curves to begin with?), I have to know which channel to move, where on each channel to move, how much to move, how many channels to move, etc.

I don’t agree that curves are tedious. I think they are fun and I have managed to convince others of this countless times in my class. I think you’re overstating the complexity, and not really describing how curves are
normally used. Much of the changing and rearrangement of curves is experimental in nature. It is a process of feedback and compromise based on
how the image looks, and how the numeric color values change. For example,
I will often try using an S curve and an inverted S on an image to see which
looks best.

When a correction requires multiple point
moves, your curves window can stay open for quite a while. And that’s assuming that you have analyzed the problem correctly BEFORE moving curves, and that you DON’T change your mind later. Unwinding all (or some of) your curve corrections and starting over again is a REAL drag. Pardon the pun.

But these objections are the same for any color correction method, whether it involves curves or not. Although it helps, there is no need to predict anything before using curves, and Photoshop’s history mechanism makes undoing of previous curve operations simple. Starting over again is as simple as ctrl-Z, and you may use history, adjustment layers or re-load a curve file if you want to modify your previous curves.

– While curves let you increase contrast for one part of the image, it is at the expense of decreasing contrast somewhere else. Sometimes the tradeoff is not easy or desirable.

But the whole goal of using curves is to perform exactly this kind of trade-off: adding color and contrast to some areas of an image, while taking
it away from others.

– Correcting for contrast with curves may screw up the colors, and vice versa.

This is a true, and often ignored, fact about the RGB and CMYK master curves – they can cause unwanted changes to color hues, and should not really be used. Lab avoids this problem by separating color and brightness
information into the Lightness and the a and b channels. Since changing color is generally more subtle than changing contrast, as a practical matter
the "vice-versa" portion of your statement is not a concern.

– As Margulis points out, sometimes correcting with curves within a single color space just won’t do the trick. Borrowing and blending channels from other color spaces is the solution. To do that, you better be able to walk on water.

One common way to blend channel data is by use of Selective Color. I do this all the time and it can often fix an image in a matter of seconds. And
your feet will stay dry.

– The power of curves can result in excessive data destruction (8 or 16 bits), and unnatural looking images. OK, same holds true for other tools.

I think you’ve answered your own question in that any image modificationk, by its nature, changes data values. I would add that data is not destroyed
by moving it around. If a steeper curve makes the image look better, so be
it.

(Now, why don’t $50 books tell you these things?)

Good point. That’s why we have Usenet. 🙂

I still use curves, but now also rely on other tools such as Selective Colors (which I don’t think curves can do).

Lab comes close, however I would be the last person to say curves are the only tool available.

Jay Arraich goes as far as
calling curves "abominable":

http://www.arraich.com/ps8_CurvesCommentary1.htm

Fun article – I’m always ready to enjoy a little icono-clasm :-)> But it is
inaccurate in several respects, not the least of which is the fact that Ansel Adams did not rely just on dodging and burning, but spent much time and effort manipulating the characteristic curve of both film and print by modifying developer chemistry. In fact, changing paper grades is very much
like using Levels or Contrast – altering developing techniques, as Adams did, foreshadowed Curves.
—
Mike Russell
www.curvemeister.com

Thank you all for the in-depth replies. I used to always use curves in my scanner software and after comparison of levels vs. curves in a particular underexposed frame, I find the curve adjustment to be far superior. As I usually like to pull more from the shadow and less from the highlight, pulling the curve at a point above the center is better for me. Of course it would be great to have a perfect in-camera exposure, but here in sunny Florida the big puffy clouds going overhead caused a great variety of exposures (similar to bracketing) and wouldn’t you know it the client liked one of the dark frames best. (We did try and pause for the clouds but still snapped off a few frames before waiting for them to pass.) I have also used selective color to further adjust the magenta sweater she wore as it comes out reddish on digital. Even with film I find purple and magenta often don’t register enough blue and look reddish instead of pinkish.

I am also experimenting with a new sharpen technique I saw on the NG but have modified to my own technique.
I am making a dupe layer of my orig, put it under orig layer, oversharpen the under layer with unsharp mask, put original on top on COLOR blending mode, then erase original on the skin only, keeping it softer focus and allowing the sharpening to show through the rest. So now everything is sharper except on the skin where I don’t want it sharp. I tried using the high pass filter as the under layer but wasn’t happy with my results. And yes I do see that curves can make your whole image look crazy colors, in fact I have used this technique to make some wild looking images. Now I will use curves to make corrections as well.

Now I tried the little pencil thing in the tool and it makes breaks in the curve line but I am not sure how or when I would use that. Thankfully my photographer gives me properly exposed and focused originals most of the time.

"Mike Russell" wrote in message

wrote:

KatWoman wrote:

Does it matter which type of adjustment?

To correct exposures I find it easier to use levels. Assuming I don’t move the far left and right points (which I have been told "clips" info out of your document) is there any reason why using curves is superior?
Also I always use this on an adjustment layer so if it’s not "correct" it can be changed. I like seeing the histogram when making adjustments.
I used to like using the curve palette in my scanner software but the PS one doesn’t work similarly, it tends to make little bumpy mountains instead of a smooth overall curve, perhaps I am not using the tool well.

Bill has already provided an excellent explanation between levels and curves. Jay Arraich went one step further with his detailed article here, although its demonstration is based only on a single b/w image.
http://www.arraich.com/ps6_tips_ccontrast1.htm

Like Mike and others, I cut my teeth on curves after reading Margulis (caution: NOT for beginners, VERY opinionated, click by click tutorials
are NON-existent, you better LIKE his writing style, etc.). His theories
are excellent and made me a convert, even though I still don’t understand everything he says. For a period, I tried to rely only on curves for all my corrections. While curves are as powerful as others mentioned, I also find problems with them, such as:

– It is tedious to use curves well. For critical corrections (and if not critical, why bother with curves to begin with?), I have to know which channel to move, where on each channel to move, how much to move, how many channels to move, etc.

I don’t agree that curves are tedious. I think they are fun and I have managed to convince others of this countless times in my class. I think you’re overstating the complexity, and not really describing how curves are
normally used. Much of the changing and rearrangement of curves is experimental in nature. It is a process of feedback and compromise based on
how the image looks, and how the numeric color values change. For example,
I will often try using an S curve and an inverted S on an image to see which
looks best.

When a correction requires multiple point
moves, your curves window can stay open for quite a while. And that’s assuming that you have analyzed the problem correctly BEFORE moving curves, and that you DON’T change your mind later. Unwinding all (or some of) your curve corrections and starting over again is a REAL drag. Pardon the pun.

But these objections are the same for any color correction method, whether it involves curves or not. Although it helps, there is no need to predict anything before using curves, and Photoshop’s history mechanism makes undoing of previous curve operations simple. Starting over again is as simple as ctrl-Z, and you may use history, adjustment layers or re-load a curve file if you want to modify your previous curves.

– While curves let you increase contrast for one part of the image, it is at the expense of decreasing contrast somewhere else. Sometimes the tradeoff is not easy or desirable.

But the whole goal of using curves is to perform exactly this kind of trade-off: adding color and contrast to some areas of an image, while taking
it away from others.

– Correcting for contrast with curves may screw up the colors, and vice versa.

This is a true, and often ignored, fact about the RGB and CMYK master curves – they can cause unwanted changes to color hues, and should not really be used. Lab avoids this problem by separating color and brightness
information into the Lightness and the a and b channels. Since changing color is generally more subtle than changing contrast, as a practical matter
the "vice-versa" portion of your statement is not a concern.

– As Margulis points out, sometimes correcting with curves within a single color space just won’t do the trick. Borrowing and blending channels from other color spaces is the solution. To do that, you better be able to walk on water.

One common way to blend channel data is by use of Selective Color. I do this all the time and it can often fix an image in a matter of seconds. And
your feet will stay dry.

– The power of curves can result in excessive data destruction (8 or 16 bits), and unnatural looking images. OK, same holds true for other tools.

I think you’ve answered your own question in that any image modificationk, by its nature, changes data values. I would add that data is not destroyed
by moving it around. If a steeper curve makes the image look better, so be
it.

(Now, why don’t $50 books tell you these things?)

Good point. That’s why we have Usenet. 🙂

I still use curves, but now also rely on other tools such as Selective Colors (which I don’t think curves can do).

Lab comes close, however I would be the last person to say curves are the only tool available.

Jay Arraich goes as far as
calling curves "abominable":

http://www.arraich.com/ps8_CurvesCommentary1.htm

Fun article – I’m always ready to enjoy a little icono-clasm :-)> But it is
inaccurate in several respects, not the least of which is the fact that Ansel Adams did not rely just on dodging and burning, but spent much time and effort manipulating the characteristic curve of both film and print by modifying developer chemistry. In fact, changing paper grades is very much
like using Levels or Contrast – altering developing techniques, as Adams did, foreshadowed Curves.
—
Mike Russell
www.curvemeister.com

I thought I cross posted to the PS groups, sorry to you Illy people I didn’t mean to put this into your NG.

"KatWoman" wrote in message

Does it matter which type of adjustment?

To correct exposures I find it easier to use levels. Assuming I don’t move the far left and right points (which I have been told "clips" info out of your document) is there any reason why using curves is superior? Also I always use this on an adjustment layer so if it’s not "correct" it can be changed. I like seeing the histogram when making adjustments. I used to like using the curve palette in my scanner software but the PS one doesn’t work similarly, it tends to make little bumpy mountains instead of a smooth overall curve, perhaps I am not using the tool well.

"KatWoman" wrote in message

Does it matter which type of adjustment?

Yes. Sometimes one is better; sometimes the other. It all depends on what you need to do to the image.
Jim