Level vs Curves, again

wrote in message

There was a "Levels vs curves" thread here awhile back, and I posted the following link by Jay Arraich who has the guts to describe curves as "abominable".

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

Now there is a post in an ongoing "emulsion side down and histograms" thread in comp.periphs.scanners that seems to agree with Jay’s comment. It also dispels the common wisdom that Curves can do everything Level can.

It can, and this has been demonstrated many times.

The first paragraph in the following post was describing the operation of Level. The meaty part is at the end.

Let the debate begin, again.

If you’re really interested in this, have you done your own experiments, and can you show us any images that you base your conclusion on?

If not, then what is the point of trying to convince you of something, when the whole point is to use the tool yourself to produce better images? —
Mike Russell
www.curvemeister.com

It also dispels the common wisdom that Curves can do everything Level can.

I don’t think this is true. Can you provide an actual image that is edited with Curves and also with Levels that demonstrates what Levels does that Curves cannot?

In article , says…

There was a "Levels vs curves" thread here awhile back, and I posted the following link by Jay Arraich who has the guts to describe curves as "abominable".

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

Now there is a post in an ongoing "emulsion side down and histograms" thread in comp.periphs.scanners that seems to agree with Jay’s comment. It also dispels the common wisdom that Curves can do everything Level can.

The first paragraph in the following post was describing the operation of Level. The meaty part is at the end.

Let the debate begin, again.

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In article , writes

Kennedy McEwen wrote:

The left-most triangle controls where the black point is. The right-most triangle controls the white point. The central triangle controls the gamma that is applied to the data between those two points. Only the central triangular control adjusts gamma, the other two controls do not affect gamma at all. When the central triangle is equidistant from the black and white point triangles then the gamma is set to 1. As the central control moves towards the white point, the gamma reduces and as it moves towards the black point the gamma increases.

From this description, I will conclude that there is only one formula in level, regardless of which points are moved.

Yes

Does the same statement holds true for Curves?

No – the curves controls are much more flexible in that a transfer function can be defined which is the cubic spline through the defined points. There are no gamma adjustment controls in the curves dialog of PS, although predefined gamma curves can be created and loaded as required.

I’m aware that curves offer more flexibility over level, and always thought that any edits done with level can be done with curves, but not vice versa. In the case of gamma adjustment, isn’t moving the level’s mid point the same as moving the curves’ mid point (vertically up and down)?

Create a step wedge image with about 10 steps. To make things easier do this in grayscale.
Point some markers on several middle patches. Duplicate the image. Take the original and apply whatever levels adjustments you wish. Now open the duplicate and adjust the curve so that the values at the markers match those on the altered levels version.
Move the markers around and repeat until you have matched all ten steps.
Look at resulting curve, it now does the same thing as th levels adjustment did and you can see what shape it is.
This will work for any levels adjustment you choose.
Curves are a superset of levels.

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

There was a "Levels vs curves" thread here awhile back, and I posted the following link by Jay Arraich who has the guts to describe curves as "abominable".

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

The author of that article conveniently overlooked contrast masking, a rather well known wet-darkroom technique.

It may be helpful to take a hint from the old B&W photography definition of Gamma as the slope of the straight-line part of the characteristic curve of a developed negative. Then, higher gamma value equals steeper slope equals greater contrast.

In this kind of simplified way of looking at things, the gamma is the mathematical tangent (y/x or rise over run) of this straight-line section of the curve. Steeper slope = higher gamma number = greater contrast. Example: – Because the tangent of 45 ° = 1.0, a 45-degree line has a gamma of one.

So far, so good, but…

In fact, there is no "straight-line part of a characteristic curve" whether it be a B&W negative, a monitor response curve (how much light out for how much signal voltage in,) a digital image or the human eye. The output of any of these systems (I mean the result…what you sense or see or measure) is non linear. That means that twice as much input (voltage or light or color intensity, for example) does not produce twice as much output (or 3X as much, or 1/2 as much or k times as much where k is any number of your choice.)

In the simplified example above, k is the tangent of that slope angle, the rise over the run.

The actual response of these systems is a curve…not a straight line. And, to make things messy, the curve is different at different input and output levels, a complex curve called a transfer function. This is the REAL curve (that you don’t see.)

The straight line you see when you open the curves dialog box is simply a linear "starting point" so to speak that’s sort of "laid over" the more complex transfer function (the REAL curve with no straight-line section.)

When you adjust that straight line in CURVES, you are really changing that underlying, complex curve. (The REAL curve.)

To me, that’s the reason that very slight corrections applied by lifting, dropping or otherwise distorting this straight line have large effects on the image.

And, because the levels center slider can only operate on a single point of the REAL curve (that hidden, actual response curve,) it has a more limited control than does curves with its ability to change different parts of that underlying (REAL) curve.

Yes, there are mathematical treatments of this subject and there are complexities that extend far beyond this explanation. And, yes, the transfer functions of all the devices in the system contribute to the output. Please elaborate if you wish. I’m simply trying to create a simplified approach to LEVELS vs. CURVES and I didn’t think it necessary to go there.

PixmakerinFLL
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wrote in message

There was a "Levels vs curves" thread here awhile back, and I posted the following link by Jay Arraich who has the guts to describe curves as "abominable".

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

Now there is a post in an ongoing "emulsion side down and histograms" thread in comp.periphs.scanners that seems to agree with Jay’s comment. It also dispels the common wisdom that Curves can do everything Level can.

The first paragraph in the following post was describing the operation of Level. The meaty part is at the end.

Let the debate begin, again.

The Arraich site stated:
(The photoshop user will say):
"That light isn’t right," jump into the curves dialog, slap a dot (or two.or three, or four.) onto a line in a two inch square proxy, drag it this way and that, eyeball the picture and say, "much better!" As if he or she knows more about light than light itself.

Is it really a question of knowing more about light than light itself, or is it a question of ‘improving’ the photograph? Seems like all the tools have a functional capability to "improve" (in the artist’s eye) the quality of the photograph……isn’t THAT what it is really all about?

On Fri, 08 Jul 2005 12:05:11 GMT, wrote:

Now there is a post in an ongoing "emulsion side down and histograms" thread in comp.periphs.scanners that seems to agree with Jay’s comment. It also dispels the common wisdom that Curves can do everything Level can.

So, show us an image where levels can do something curves can’t. Actually, curves give you finer adjustment than levels because you have 256 possible points of adjustment instead of three (or how ever many you manage to fit on the slider bar.).

—

Hecate – The Real One

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