Curves In Photoshop

[george_doumani]

I am quite an advanced Photoshop user but I have managed to achieve acceptable results for many years

without really understanding or using the curves option.

 

Can anyone point me to a resource on the web which will give me an indepth insight into what i should be

doing with "curves"?

 

many thanks

[errol young]

You should learn to use curves and so should I.

 

I usually use levels because I can see the histogram. I have started to use the luminosity mask with it on an ajustment layer. (Type ~and Control at the same time.) then invert it and levels again. It give an ability to fine tune the ajustment.

 

Errol

[emre]

What do you do when one part of the image is too bright, too contrasty, or has a cast?

[keith_clementson]

In curves if you option (alt) click inside the grid, it makes the grid 10 up and 10 across. Then

you can control the brightness of the individual zones - a huge advantage in some cases if

you think in terms of the Zone System. Curves offers more sophisticated control of contrast.

A simplified, entry-level video (free) can be downloaded from http://www.radiantvista.com/

 

Download the "adjustment layers" video. It's well done and an excellent training tool for

curves noobs. (I am not associated with them in any way.)

[bobmichaels]

I work in black & white almost exclusively and can say that the shape of the curve is THE most important part of a b&w print. EVERY print I do has a layer for a curves adjustment.

 

The levels adjustment is somewhat mechanical and can be done moderately well with the auto setting, although I always do it manually.

 

Photoshop's ability using curves to adjust the contrast in the highlights, midtones, and shadows independent of each other is what sets the digital print process ahead of using the wet darkroom.

 

FWIW, my curves are almost always S shaped, seldom simple concave or convex. They almost always have 2 points (excluding the end points). Using only two points enable smooth transitions. The placement of those points establishes the independent highlight / midtone / shadow contrast as well as well as when one begins to transition to another in b&w.

[frans_waterlander]

"Quite an advanced Photoshop user" who doesn't really understand or use Curves? You gotto be kidding! Educate yourself and fast before you aquire more bad habits; for instance, do you use the Contrast tool for increasing contrast? That's a big no-no. I can highly recommend the book "Real World Photoshop"

[george_doumani]

No Frans i never adjust contrast via the contrast tool. I always work within my layers and

select the channel i feel provides the best contrast for the area i feel needs a "nudge", i copy

that layer and adjust the contrast via that copied channel than I either mask or blend the

layer.

[matt_needham]

"I usually use levels because I can see the histogram."

 

If you have the histogram window open when using curves you can see the histogram change as you adjust the curve.

 

"What do you do when one part of the image is too bright, too contrasty, or has a cast?"

 

You could select that area using a feathered lasso, but I find it easier to make an identical layer, adjust as necessary, and then paint in the area using masking.

[DickArnold]

Frans. Your sarcasm is why more people don't ask for help. I flew airplanes professionally for forty one years and was still confessing ingnorance the day I retired. There are many gaps in my digital knowledge even though I owned and operated my own phtography business. The way to learn is to ask what may appear to be stupid questions to others.

[emre]

You color correct by painting?

[Brad_]

I've found that many times Levels in combination with Shadows/Highlights does a pretty

good job.

 

No doubt a "bad habit" and "no-no" one of the above experts will go into cardiac arrest

over...

[bwcombs]

Here are a few links with some curves info:

 

http://www.cambridgeincolour.com/tutorials/photoshop-curves.htm

 

http://www.youtube.com/watch?v=BXUTCkk7N74

 

[frans_waterlander]

George wrote: "No Frans i never adjust contrast via the contrast tool. I always work within my layers and select the channel i feel provides the best contrast for the area i feel needs a "nudge", i copy that layer and adjust the contrast via that copied channel than I either mask or blend the layer."

 

A single application of some kind of s-curve in Curves will do the trick in most situations.

[frans_waterlander]

Dick wrote: "Frans. Your sarcasm is why more people don't ask for help."

 

Give me a break, will you? People shouldn't start using layers and masks before they understand and can effectively apply the simpler tools like Curves. If I offended you by speaking my mind, then so be it.

[george_doumani]

come on guys.... cool it

 

lovely to see some emotion in the air though!

 

btw..... thankyou all for your contributions

[DickArnold]

George. Frans. I am not offended nor am I angry. Just a voice for all of us who make dumb mistakes in CS3. In spite of admitted clumsiness, I do make very nice exhibition quality prints. A few are posted in my gallery as is my spotty photo bio. I use curves but never got into the zen of using them. Maybe sanctimony will help me with them and Frans is obviously right with what he says. To me curves just helps me with my pictures. I recently bought a new monitor and computer and am delving deeply into the arcane world of monitor calibration, and have ordered Spyder, because, although I like my new 22 inch Samsung I cannot consistently keep it calibrated. I get it just right for a few prints and then, as it had a mind of its' it turns cyan or yellow on me until I fool with it and get it back on track. I am trying to determine whether it's the monitor, the paper, the printer, or sRGB, Adobe RGB, or Samsung RGB that's the culprit. Color managment is a whole nother subject. Bruce Fraser wrote a great book about it and maybe I'll get it. Then there is the zen of sharpening which I bypassed by getting Photokit Sharpener which makes sharpening a mindless, unemotional operation for me. I am too old to hold a grudge for over five minutes. My wife, unfortunately knows that. What I guess really counts is what hangs on the wall or my satisfied customers that I served for quite a few years.

[DickArnold]

No masks, no layers, just nice light. Mostly done in the camera with a good lens.<div></div>

[steve_vanslow]

George,

Always use curves as an adjustment layer. So you can always go back and make changes to

it. S- curves are good for adding contrast but only the mid-tones will get the contrast.

The more vertical the curve the more contrast. In an s-curve you will decrease the contrast

in the high and low end. Better to move the end points in to make the whole "curve" more

vertical and then "paint" back in highlights and shadows with a mask. Adding contrast also

effects saturation, so put the blending mode to luminosity. When adjusting color you can

use the "color" mode put it's not as necessary. Always do tonal and color corrections with

separate layers. I hope this helps.

Steve

[george_doumani]

thanks Steve, i'm already getting better results with just playing around a little with those

ideas

 

cheers

[frans_waterlander]

A couple of comments on Steve Vanslow's post:

 

1) Adjustment layers are great, but not always necessary, particularly when doing limited editing. I only use them for complicated editing situations.

 

2) Which area(s) of the image will increase in contrasts and which will decrease depends on the shape of the s-curve applied. Any area of the tonality curve can be increase in contrast, not just the mid-tones.

 

3) Whether it is better to move the end points in depends on how far away those points are from 0 and 255 because of potential clipping of tonal values. And if those end points haven't been moved yet to stretch the image information across the entire tonality range, then Levels is a way better tool to do this.

 

4) I'm at a loss about what looks to me like a description of first compromising the shadows and highlights and then trying to save them by "painting them back with a mask". In my opinion, Levels and Curves will accomplish whatever corrections to the tonality of the image are needed.

[steve_vanslow]

"1) Adjustment layers are great, but not always necessary, particularly when doing limited editing. I only use them

for complicated editing situations."

 

First, I always create a "Master File" that uses layers for everything I do. This file uses layers for everything from

spotting, to color correction, to tonal adjustments, to dodging and burning, and ANYTHING else I do to an image. I

can always go back and tweak any part of anything I have done, be it 5 minutes ago, yesterday, or 3 years ago. I can

tweak it to print on an inkjet, to print a lightjet, to e-mail, or to publish. During all of that my background layer

remains UNTOUCHED. If in a couple of years, a new software, a new printer technology, or I take a class or read a

new book and want to try something new on an old image, I can do so without having to re-do and re-create

everything. You can always flatten and save as another file for whatever output you want to use. Yes, this makes for

a large file, but storage is cheap, RAM is cheap. Every time you make an adjustment to the background layer, you

permanently change the file. You can never get those pixels back. If you do that often enough, your image will

degrade.

 

"2) Which area(s) of the image will increase in contrasts and which will decrease depends on the shape of the s-

curve applied."

 

An "S" curve, by definition has the shape of an "S". The top part ( the highs- 255s) and the bottom part (the

shadows- 000) get more horizontal. The middle of the curve gets more vertical. Now, as I said, the more horizontal

a curve, the more it reduces the contrast. The more vertical a curve, the more it increases the contrast.

 

"Any area of the tonality curve can be increase in contrast, not just the mid-tones."

 

True. But if you use an "S" curve, you will decrease the contrast in some area.

 

"3) Whether it is better to move the end points in depends on how far away those points are from 0 and 255 because

of potential clipping of tonal values."

 

I'll come back to this one.

 

"And if those end points haven't been moved yet to stretch the image information across the entire tonality range,

then Levels is a way better tool to do this."

 

I disagree. Curves can do everything levels can do and do it better with finer control.

 

"4) I'm at a loss about what looks to me like a description of first compromising the shadows and highlights and

then trying to save them by "painting them back with a mask". In my opinion, Levels and Curves will accomplish

whatever corrections to the tonality of the image are needed."

 

When I do my tonal corrections, I will use a curve adjustment layer. I move the bottom point ( the shadows ) and the

top point ( highlights ) in so that 90% of the image looks like I want it, ignoring the clipping going on in the shadows

and highlights. I then click on that layer mask ( the white box on the curves layer in the layers pallet) and using a

brush of varying sizes and opacities, with black as my selected color, "paint back in" the highlight and shadows. I

take care to blend it all in nicely. This way you can have your nice contrast in the midtones and still "save" the

contrast in the highs and lows. And remember to put the blending mode to luminosity or you will get saturation in

the colors as well.

 

Now, I didn't invent any of these techniques or ideas. I learned all of this from people much smarter than me and

masters of their craft. I'm not saying this how it has to be done, but it's how I was taught and it works for me and

my use of photography.

 

Cheers,

 

Steve

[jack_franklin]

Steve, thank you for sharing that information in such detail. This was not my post

(question) but I have always wanted to know more information about curves. Your generous

post is greatly appreciated.

 

JF

[frans_waterlander]

Steve,

 

Like I said, layers are great when you need them.

 

There are many different s-curves. For instance, you can apply an s-curve to increase or decrease the contrast in the shadow and/or highlight areas only. There can be more than one s-shape in what is generally refered to as an s-curve. So no, an s-curve does not necesarily increase (or decrease if the s is inverted) the contrast in the middle area only at the expense of the shadows and/or highlights.

 

Curves is no replacement for Levels. For most people it is way easier for instance to tweak the darkest and brightest points in Levels than it is in Curves. Most people are better of using both tools, first Levels, then Curves.

 

The complicated method you discribe can easily and more effectively be replaced by a single adjustment step in Curves. No need to go back and painstakingly paint back details using a brush of varying sizes and opacities.

 

If I may be so blunt, it appears to me that you have picked up a couple of bad habits. Do yourself a favor, buy the Real World Photoshop book, forget everything you know up to now, start reading and learning.

[steve_vanslow]

Wow, Frans,

Ummm Ok.

 

I was just trying to help, but , hey, I'll just keep it to myself next time. I'll be busy reading.

 

Cheers,

 

Steve

[frans_waterlander]

Steve,

 

I'm sure you were trying to help and so was I by expressing my disagreement with what you said. Nobody benefits is we don't speak up for fear of offending.