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So, if you want to brighten or darken images that are a little too dark or light, and/or increase contrast, first use Levels - Histogram and then Curves to adjust exposure (articles Part II and Part III). Then if you want to adjust colors use Color Balance (Part IV). And Hue/Saturation is the next tool you might use to fine tune color. My plan is to use the tools in order and make small changes with each tool, so at the end I have achieved subtle yet definite improvements, while I keep the picture looking natural. It takes some practice and judgement developed from practice. Look at the image critically first and decide how it might be improved. You may not want to use all of these steps, but to know how you can improve an image you need to know what the tools can do.
Click on "Image" on the menu bar, then "Adjustments" (or "Adjust") and "Hue/Saturation..." to see the Hue/Saturation tool. Figure 1 shows two views of the dialog box, one with the default Edit: Master selection which allows you to modify the entire color range, and the second showing the Edit: dropdown list where you can select which colors to edit:
Figure 1
Move the Hue slider back and forth, and the colors shift. Move the Saturation slider to the right and colors get more saturated, primary colors more concentrated; move it to the left and colors get less intense. And the Lightness slider controls overall brightness, which is useful when you are editing individual color ranges selected from the dropdown list. With Edit: Master selected, using the Lightness slider to change overall brightness is a bad idea - instead go back to Levels - Histogram or Curves to adjust overall exposure.
Here are a couple of extreme examples (Figure 2) to show Hue changes with Edit: Master selected, the first with Hue at -60 and the second with +60. Notice how the colored bar along the bottom moves as the Hue slider moves, to indicate the amount of color shift occurring.
Figure 2
And Figure 3 is an extreme example showing the Saturation slider moved to +50 with Edit: Master selected:
Figure 3
The first thing you might want to do when you use Hue/Saturation at first is crank that Saturation slider up to see the colors "pop" out. It seems like an easy way to punch up a picture - but fight the power! (Put down the pliers, Eugene!) By increasing saturation too much, you are concentrating colors into the primary colors and starting to wipe out the secondary, more subtle colors. The results can begin to look garish and unnatural as in the last example above. If you want special effects then have fun, but my intent is to enhance and keep it natural.
Here’s an example of how I might use Hue/Saturation instead. I have made some Levels and Curves adjustments to the picture of the hogfish in the examples above on the left. Thinking about color, I then decided I wanted to accentuate the reddish brown color on the fish a little, and I wanted to dial out some green since the background is so green. So I selected Red from the Edit: dropdown list and fiddled with the sliders a bit (left side of Figure 4). I decided a slight Hue shift of -4 made the reds a little more reddish brown, a Saturation increase of +6 made them a bit bolder, and a Lightness change of -6 made them a bit darker so they stand out a bit more compared to the light colors on the fish. There are virtually no reds in the background so these changes affected only the fish.
With the tool still open, haven’t click the OK button yet, I selected Green from the Edit: dropdown list (right side of Figure 4). I turned down Saturation slightly to -8 and Lightness to -2. The fish has some green, such as the eye, and I didn’t want to change that too much, so these were pretty slight changes. If I wanted more change to the green background while leaving the green on the fish alone, I could have used a selection tool such as the Lasso or Magic Wand to select only the background, then I would Feather the selection by some pixels so my changes would blend smoothly, and then use Hue/Saturation only on the green background.
Figure 4
Figure 5
These are very slight changes and the result may not be very obvious. But after I made small changes with Levels - Histogram, then Curves and finally Hue/Saturation I can see a visible improvement.
Previous: Digital Imaging Editing - Part IV
Next: Selective Enhancement of Images - Part I
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