Curves display

Don wrote:

Version 6.1:

In order to help me grasp Curves better I’d like to see the effects of other adjustments (brightness, hue, etc) plotted on the Curves display. How do I do that?

Example: Let’s say I make some contrast adjustments. What would a curve display look like to achieve that very contrast adjustment?

Don,

Some adjustments, such as brightness/contrast, are fairly simple to translate to curves – a steep curve means more contrast for example, and moving the entire curve up or down corresponds to brightness. Levels is similar to a curve with three control points. (Neither contrast nor brightness should normally be used on an image, since there are better controls available.)

Other adjustments, such as hue, selective color, etc, have no representation on a curve at all. For example, if you change the hue of an image, there is no such curve in RGB space. This happens because the new value of Red for a particular pixel depends on the amount of Green and Blue in that pixel.

FWIW, even in HSB space, which once existed in Photoshop, the curve would have a break at the 0-360 point.

—

Mike Russell
http://www.curvemeister.com
http://www.zocalo.net/~mgr
http://geigy.2y.net

Some adjustments, such as brightness/contrast, are fairly simple to translate to curves – a steep curve means more contrast for example, and moving the entire curve up or down corresponds to brightness. Levels is similar to a curve with three control points. (Neither contrast nor brightness should normally be used on an image, since there are better controls available.)

Thanks Mike, as always!

I’m assuming you’d use curves to set contrast and brightness by targeting specific areas of the image but how do I identify which areas of the image correspond to which areas on the curve?

Of course, broadly speaking, they are self-evident but I’d like a more exact method than just poking around a general area until the image "looks right". Nothing wrong with that to get the overall feel, but I’d like something more efficient and direct.

What I’m getting at is a procedure similar to, say, setting the white and black points whereby – instead of guessing – threshold is used to identify those points exactly. Setting W/B points may be a blunt instrument but I like the use of threshold to identify them.

Is there a similar method with curves to not only identify an area to be corrected but also where to put "anchor" points around it in order to limit the adjustment to the desired area?

Don.

I’m assuming you’d use curves to set contrast and brightness by targeting specific areas of the image but how do I identify which areas of the image correspond to which areas on the curve?

You can use the inof palette and drag the cursor over the area in question, or set eyedropper sample points in the info palettes. While in curves, click and drag on the image to highlight that point on the curve.

Just what the doctor ordered! My Nikon scanning software does this automatically, i.e. without click and drag and I just knew there must be something similar in Photoshop. Thanks very much, Mike!!!

Don.

when you say "drag" , you mean click , hold and move , right ???

"Mike Russell" wrote in message

Don wrote:
…

Thanks Mike, as always!

you’re very welcome.

I’m assuming you’d use curves to set contrast and brightness by targeting specific areas of the image but how do I identify which areas of the image correspond to which areas on the curve?

You can use the inof palette and drag the cursor over the area in

question,

or set eyedropper sample points in the info palettes. While in curves, click and drag on the image to highlight that point on the curve.

Of course, broadly speaking, they are self-evident but I’d like a more exact method than just poking around a general area until the image "looks right". Nothing wrong with that to get the overall feel, but I’d like something more efficient and direct.

What I’m getting at is a procedure similar to, say, setting the white and black points whereby – instead of guessing – threshold is used to identify those points exactly. Setting W/B points may be a blunt instrument but I like the use of threshold to identify them.

Clicking and dragging on the image while adjusting curves is probably the most common way to determine the range of an object in your image – drag

the

cursor across an area of interest, such as a face, and see the range it occupies in that channel. You may have to resort to writing the numbers down. In CMYK mode you’ll find, BTW, that each color occupies a smaller piece of the curve, and so may be curved more agressively than the corresponding region in RGB mode.

Is there a similar method with curves to not only identify an area to be corrected but also where to put "anchor" points around it in order to limit the adjustment to the desired area?

Anchor points may be added manually, or you can have curve files saved to lock down the diagonal before you start. I use this technique in Lab mode to do selective color moves, or to lock down half of the a or b channel,

for

example to limit my changes to steppenining the green only in one half of the curve while keeping magenta where it is.

BTW – you still need to maintain your neutrals and other important colors while doing curve steepening for a particular region of a curve. As

always,

grab any book by Dan Margulis to get more info and examples.
—

Mike Russell
http://www.curvemeister.com
http://www.zocalo.net/~mgr
http://geigy.2y.net

wrote:

when you say "drag" , you mean click , hold and move , right ???

Right you are.

—

Mike Russell
http://www.curvemeister.com
http://www.zocalo.net/~mgr
http://geigy.2y.net

Last summer I asked the question below and by sheer serendipity I just discovered a program which converts levels into curves:

http://www.marginalsoftware.com/Download/

The program is called: "Level2Curve".

I hope someone finds it useful. I wasn’t able to contribute much here until now so this is just a tiny downpayment for all the help I got.

Don.

—

On Sat, 30 Aug 2003 03:44:43 GMT, (Don) wrote:

Version 6.1:

In order to help me grasp Curves better I’d like to see the effects of other adjustments (brightness, hue, etc) plotted on the Curves display. How do I do that?

Example: Let’s say I make some contrast adjustments. What would a curve display look like to achieve that very contrast adjustment?
Don.

On Sat, 25 Oct 2003 20:41:29 GMT, (Don) wrote:

Last summer I asked the question below and by sheer serendipity I just discovered a program which converts levels into curves:

http://www.marginalsoftware.com/Download/

The program is called: "Level2Curve".

I hope someone finds it useful. I wasn’t able to contribute much here until now so this is just a tiny downpayment for all the help I got.
Don.

—

On Sat, 30 Aug 2003 03:44:43 GMT, (Don) wrote:

Version 6.1:

In order to help me grasp Curves better I’d like to see the effects of other adjustments (brightness, hue, etc) plotted on the Curves display. How do I do that?

Example: Let’s say I make some contrast adjustments. What would a curve display look like to achieve that very contrast adjustment?
Don.

This post is waaay late to this conversation (thanks Earthlink for the great post longevity, but:

Wow, this is a really neat app! I’m just learning to work with curves too and this is a great help for understanding what’s going on.

Clopixe wrote:

On Sat, 25 Oct 2003 20:41:29 GMT, (Don) wrote:

Last summer I asked the question below and by sheer serendipity I just discovered a program which converts levels into curves:
http://www.marginalsoftware.com/Download/

The program is called: "Level2Curve".

I hope someone finds it useful. I wasn’t able to contribute much here until now so this is just a tiny downpayment for all the help I got.
Don.

—

On Sat, 30 Aug 2003 03:44:43 GMT, (Don) wrote:

Version 6.1:

In order to help me grasp Curves better I’d like to see the effects of other adjustments (brightness, hue, etc) plotted on the Curves display. How do I do that?

Example: Let’s say I make some contrast adjustments. What would a curve display look like to achieve that very contrast adjustment?
Don.

This post is waaay late to this conversation (thanks Earthlink for the great post longevity, but:

Wow, this is a really neat app! I’m just learning to work with curves too and this is a great help for understanding what’s going on.

Clopixe,

Here’s a fun plugin for playing with and learning about curves. If I do say so myself 🙂

http://curvemeister.com/downloads/

Install the Curvemeister Demo plugin, click the round button in the upper right corner, then check out the tutorials under the Help menu.

If you just want to read the tutorials, use this link:
http://curvemeister.com/support/curvemeister/help/

—

Mike Russell
www.curvemeister.com
www.geigy.2y.net