Curves in Photoshop

An overview of the Curve Dialog Box

Curves can be thought of as a very enhanced version of levels. In practice, however, levels is a stripped down version of Curves. When you apply the levels command Photoshop converts that to a curves command. Photoshop Elements does not have the curves feature. However a plugin is available that will allow you to use curves in Elements. Check the end of this handout for details.

By default, the curves dialog box will come up as it is in the graphic on the right (without the labels on the points.) And you will have to add the Shadows, Midtones, and Highlights points on the curve. Also, the new CS3 has a little different look to the Curves Dialog Box. But not enough changes to keep anyone from using it.

By moving a point up, down, left, or right you may change the tonal quality of points whose tonal values are represented by that point on the curve. Moving a point up causes the image to lighten and moving a point down causes it to darken. Moving a point left or right causes the input value to change.

You can fix a point in two ways. The most common is to click on the curve to set a point. The second is to put your cursor over the image (the cursor will change to an eye-dropper) and doing a ctl-alt-click on a point. A point will be set at the tonal value of that point. You can make a point active by clicking on the point. You can move a point by dragging or by using the arrow keys. You may remove a point by dragging it off the curve box.

Doing Levels using Curves

You might ask why do levels using curves -- just do levels. And, of course, you would be right if all you wanted to do was levels. But learning to do levels in curves is a good way to start using curves.

Since the Curves dialog box does not have a histogram like levels (it does in CS3) you need to bring up the histogram pallet so you can see what you are doing.
Move the top right point (the white point) to the left until the histogram moves to the right edge of the histogram pallet. This is equivalent to moving the right slider to the left in levels.
Move the lower left point (the black point) to the right until the histogram moves to the left edge of the histogram pallet. This is, of course, equivalent to moving the left slider to the right in levels.
Now set the midtones point by clicking on the curve at the middle vertical guide line. This point will become the same as the midtone slider in levels. You may adjust the midtones by moving that point up or down until you get the desired effect.

Adjusting the Contrast in Curves

To increase the contrast in am image you need to make the dark portions of the image darker and the light portions lighter. And you also need to be careful not to blow out the highlights or block out the shawdows. To do this using curves take the following steps:

Set the shawdows, midtones, and highlights points as in the graphic at the top of this lesson.
To increase the contrast move the highlights point down and the shadows point up. Note that this gives you much more control than you have in the brightness/contrast tool since you can adjust the highlights and shawdows separately.
To decrease the contrast move the highlights point up and the shadows point down.

Making Finer Adjustments

Open an image and after you have made some of the basic adjustments as described above you may then start to make some finer adjustments.

Start by holding the control key down and moving the cursor over the to a point that you would like to adjust. It might be a dark point you would like to lighten or a highlight that needs darkened. You will notice a floating point on the curve that corresponds to the image values you are moving the cursor over.
When you find a point to adjust press alt-ctrl-click to set the point on the curve.
You may then darken or lighten the point you have selected by moving that point up or down.
When you move the point a broad portion of the curve moves. It this is excessive you should add another point near the one you have selected to anchor the curve.

Adjusting Color with Curves

You may also adjust the red, green, and blue color tones in an image. For example, if your image is too red choose "Red" in the Channel drop down menu. Then the adjustments you make will effect only the reds in your image. Start out by selecting the midtones and moving it up or down. This normally will be sufficient. But you could also give your image more (or less) red contrast and even modify individual areas for red. And, of course, this same concept applies the the blue and green channels.

Web Resources on Curves

The following are some of the resources that I found on the web to help me prepare this handout and lesson. In most of these sites the first link is to a fairly large group of tutorials on Photoshop or Elements that are on that site. The second link is to a tutorial on curves.

Netscape Search (will work with Internet Explorer)

http://keyword.netscape.com/ns/search?fromPage=nsBrowserRoll&query=photoshop%20curves

Cambridge in Color

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

The Luminous Landscape

http://www.luminous-landscape.com/tutorials/
http://www.luminous-landscape.com/tutorials/command_primer.shtml

The Golden Mean

http://www.thegoldenmean.com/technique/techniqueIndex.html
http://www.thegoldenmean.com/technique/curves1.html

Earth Bound Light

http://www.earthboundlight.com/phototips.html
http://www.earthboundlight.com/phototips/photoshop-curves.html

Secrets of Digital Photography

http://digitalsecrets.net/secrets/index.html
http://digitalsecrets.net/secrets/curves.html

Creative Pro

http://www.creativepro.com/front/home
http://www.creativepro.com/story/feature/18117.html?origin=story

Nikon Digital

http://www.nikondigital.org/
http://www.nikondigital.org/articles/curves_russell/index.htm

YouTube (believe it or not -- a pretty good video on curves with links to other videos on photoshop)

http://www.youtube.com/watch?v=ORM6AZY19pw

PictureLine News

http://www.pictureline.com/
http://www.pictureline.com/newsletter/article.php?id=25 (curves, part I)
http://www.pictureline.com/newsletter/article.php?id=35 (curves, part II)

Curves for Photoshop Elements

Photoshop Elements (all versions) can do most of what Photoshop CS can do. But one feature that many wish they had is curves. Now you can have curves in Photoshop Elements (versions 3, 4, & 5) with SmartCurves. SmartCurves has some features that even the Photoshop CS versions do not have. The main drawback is that you do not have a curves adjustment layer. But what the heck -- its free! An Al Crawford will tell you how to use curves in the Advanced Digital Photography Workshop at 1:30 this Thursday.

SmartCurves, a freeware plugin that will allow you to use curves in Photoshop Elements, is available for download at http://www.crawfordenterprise.com/Photography/Classes/smartcurve.zip. To use it copy "smartcurve.8bf" from "smartcurve.zip" to the folder C:\Program Files\Adobe\Photoshop Elements 4.0\Plug-Ins\Filters. (note: SmartCurves will also work on Elements 3 and 5).

After you have smartcurve..8bf in place restart Elements.

Curves will then be found with the following menu combination: "Filters -- easy filters -- smart curves"

Photoshop CS3 Tutorial

Want to kn ow more about the yet to be released Photoshop CS3. Deke McClelland's free tutorial on Photoshop CS3 might just be the ticket.. He goes over all of the new features of CS3 in a total of 1.5 hours of video. These are, however, broken up into topics and each topic is usually about 5 or 6 minutes each. Access these videos at http://movielibrary.lynda.com/html/modPage.asp?ID=327.

YouTube for Tutorials on Photoshop Elements

Believe it or not -- there is actually something useful on YouTube. Go to http://www.youtube.com/ then in the search box at the upper right of your screen type in "photoshop elements". You will get a large number of hits including many tutorials that are quite professional. Give it a try.