Tag Archives: Photoshop Tips

Nonlinear Curve Adjustments and Histograms

The last article on curves looked at linear adjustments and how those adjustments affect the image and the histogram. So now we’ll take a look at some nonlinear adjustments within the curves adjustment tool found in many photo editing software packages.

We’re basically building on our basic understanding of the histogram and our knowledge of linear curve adjustments to take the next step into nonlinear adjustments (the curvy curves).

NONLINEAR MANIPULATIONS

What I’m going to show here are some very basic curves at each extreme. The single bend and double bend curves are most commonly used during post-processing, but these are not the only options. Curves can have a large number of set points, bends, and inflections — it’s just not feasible to cover every possibility in an article like this.

SINGLE BEND CURVES

The simplest form of a nonlinear curve is accomplished by moving a mid-tone location toward the upper left or lower right corner, forming a basic arc with a single bend. Essentially, your black and white points remain fixed while your mid-tones become lighter or darker (aka: brightness). Also note that one end of your tones will take on more contrast while the other end will lose contrast due to the change in slope of the curve (remember: vertical = high contrast, horizontal = low contrast).

This can be used to brighten or darken the overall image if you want to maintain your highlights and shadows at their current values.

DOUBLE BEND CURVES

Also known as the “S-Curve”, this curve manipulation pushes one section of tones brighter and another section of tones darker (aka: contrast). Again, you can maintain your black and white points, but you also maintain some middle tone where the curve crosses the diagonal. On the note of contrast again, be aware that you will sacrifice contrast in one area to gain it in another.

This can be used to raise or lower the contrast of the overall image with a focus on the mid-tone areas. The bright/dark tone changes of the highlights/shadows are amplified by the mid-tone slope change — so it doesn’t take much to really change the contrast.

APPLYING NONLINEAR CURVES

The beauty of the curve adjustment is that you have such a wide range of possibilities — much more dynamic than a single slider adjustment. To apply curve adjustments, you simply click a location on the curve and drag it to the desired location. The curve will bend on its own based only on your set points. You can continue to add set points until you have the desired result.

Using the example image above (middle of series), here’s one possible curve that combines linear, single bend, and double bend curves. Keep in mind that I haven’t applied any basic adjustments and what you’re seeing is pure curves from an unprocessed raw file (except for the b/w conversion).

Notice that I used a double bend curve to increase contrast. Combine that with a single bend curve to increase brightness. And combine that with a linear adjustment to set my black and white points. I’ve also placed several extra points on the curve in order to bend it into the shape I wanted while maintaining a smooth transition.

As you work with curves, you’ll noticed that they sometimes have a mind of their own. Extra points will help shape the curve and provide you with the ability to make the adjustments you want. On that same note, too many set points can lead to choppy and lumpy curves. Non-smooth transitions generally begin to produce strange contrast artifacts that are easily seen in the image.

For you curves experts out there, what other tips and advice would you add to this discussion? How are you guys using curves to enhance your images?

A Personal Touch on Photoshop Actions

Stop Hammertime.
Creative Commons License photo credit: Rich Anderson

I’ve talked about creating Photoshop actions and using Photoshop actions in previous articles. I’ve also gone through some techniques for things like LAB Saturation, LAB Sharpening, Cross Process & Redscale, Digital Grain, and I’ve wrapped those things up in an action set.

DOWNLOAD THE EPIC EDITS PHOTOSHOP ACTIONS

But one thing that I haven’t done until recently, is add some information about who created the actions. I’ve downloaded some other action sets from various people (if you’re into downloading actions, check out Chica’s 1000+ Free Photoshop Actions), and I noticed that many of them contain a little message box with some basic information about the creator and their website. It’s a pretty simple trick, so I’ll share it here. This is particularly useful if you’re planning on posting your actions or sets to the web.

  1. CREATE A NEW ACTION FOR YOUR INFO BOX
    Palette Menu >> New Action… >> (give it a name) >> Record
    In order to record any action steps, you’ll need to create an action. Making a separate action for the information box is optional — you can also just add the info box to the action at the beginning or the end. I prefer to use the method of creating a separate action so users can easily decide if they want to see where the work came from.
  2. INSERT A STOP DIALOG
    Palette Menu >> Insert Stop

    This “stop” is what creates the message box. You’ll be presented with a dialog box to add some text, and you should also have an option to “Allow Continue”. Write whatever you want the user to see in the box — your name, your website, distribution permissions, etc. If you find yourself out of space (there is a limit to the number of characters), just check the “Allow Continue” box and add another Stop action after the first one.
  3. STOP RECORDING YOUR ACTION
    Palette Menu >> Stop Recording (or use the icon in the Palette)
    When you’re finished with your information box, make sure you stop recording. Then test it out and make sure it works the way you want it to.

This is handy for inserting information about yourself into your actions and sets, but there’s also another use for it. If you need to convey a message or set of instructions to the user during execution of the action, you can add one of these stop dialogs (with the option to Allow Continue) between any two steps in the action. First time users will see the message, while those who have used the action will have the option of turning that step off for future runs.

Are there any other good uses for the stop action dialog?