Hands-On Photoshop CS: Correcting a Problem Image
Overall color correction using adjustment layers on a problem scan without good white or black points. Using advanced selections and adjustment layers with Curves, Hue/Saturation, and Unsharp Mask to finish color correcting a problem scan; soft proofing and fixing out-of-gamut colors.
In this example, you will do overall color correction but use some different techniques than in the Banff Lake session because the histogram of this scan looks different. For the purposes of this example, we assume that you have done the Banff Lake, Chapter 19: "Overall Color Correction," example.
Figure 20.1 The initial Kansas Photo CD scan.
Setting Highlights with Channels
Step 1: Open the file KansasRawPhotoCD from the Chapter 20 folder on the Photoshop CS Artistry CD. When you get the Embedded Profile Mismatch dialog, leave this file in ColorMatch RGB space to have your color correction adjustments to match the books. The other choice would be to convert the file to Adobe RGB, which is what you would do when opening a scan with a scanner profile attached. This is a 4MB 8-bit Photo CD scan of a Kodachrome shot I took while driving through Kansas during a summer vacation when I was in college in 1977. Old Kodachromes tend to fade! In the Crop tool (C), delete the Option bar values in Width and Height if they are still there from the last exercise. Use the Crop tool to crop the copyright notice from the bottom. Choose File/Save As and save this file as KansasLayers. Put the image in Full Screen mode (F) by clicking the middle icon at the bottom of the Tools palette. Bring up the Info palette (F9 with ArtistKeys) and the Histogram palette (Shift-F9), and then choose Image/New Adjustment Layer/Levels (Command-F2) to enter Levels giving this adjustment layer the name Overall Levels.
Step 2: Look at the original RGB histogram pictured here and notice that the values don't go all the way to the right (highlight) side, which is why the picture looks dull. Press Command-1, then Command-2, and then Command-3 to look at the Red, Green, and Blue channels, respectively. I always do this when I first look at a scan to see if it has any potential problems. In this image, all the channels have dull highlights, but each of them has highlight detail that ends at a different point on the histogram. Press Command-~ to go back to RGB and then hold down the Option key while dragging the Input Highlight slider to the left. Remember, the Option key technique only works if you have the Preview checkbox on. You would normally set the highlight at the first area to turn white. In this photo, there is no good, neutral place to set a highlight, which should be pure white after that setting. The "white" buildings aren't really that white, and the brightest area is actually somewhere in the blue clouds. That's a sign that the Eyedropper may not be the best way to set the highlights in this image. Type Command-1 again and move the Red Input Highlight slider to the left until it reaches the first real histogram data, at about 213. Do the same thing for the Green (189) and Blue (171) channels, and then press Command-~ to return to RGB. Notice how much brighter the image looks now and how much more complete the RGB histogram looks. We have set our highlight for this image.
Figure 20.2 Step 2: Original RGB histogram with lack of highlight values.
Figure 20.3 Step 2: Histogram palette display of above histogram after highlights are set. The original histogram is now gray.
Figure 20.4 Step 2: Move the Input Highlight sliders of the Red, Green, and Blue histograms to the left until they touch the beginning of the data. This moves all the data to the left of that point all the way to the right, spreading out the values in each histogram. If you hold down the Option key as you move each color channel highlight slider to the left, you can see, in that color, any highlight values that will be clipped. Don't clip any values that would remove important highlight details from your image.
Step 3: Notice that the shadow values in the Blue channel suddenly drop off a cliff on the left side, unlike those in the Red and Green channels, which taper off like they should. This is a sign that the scanner did not get all the shadow detail in the Blue channel or that there was no more detail in the film. Because this is a Photo CD scan, we have to live with it or buy our own scanner. When this happens to you, look at the original transparency and see if there was actually detail in this area. If there was, you might be able to get better results by rescanning with a high-end drum scanner, a better scanner, or just better scanner settings. However, in the real world, we often have to correct problem images and scans. Back in the RGB channel, hold down the Option key and move the Input Shadow slider, the top-left slider, to the right to test for a shadow point. There are some good shadow locations on the right side of the wheat, at the bottom, and also within the big green tree by the house. Move the Input Shadow slider back to 0. Measure these shadows with the Eyedropper until you find the darkest neutral spot (I found a few in the wheat that had initial values of 5, 5, 5) and then Shift-click on that spot to create Color Sampler #1 in the Info palette. Go into each of the Red, Green, and Blue channels and move the Input Shadow slider to the right until the Color Sampler for your shadow point reads around 2, 2, 2 and your black shadows look neutral. If they don't, click a new darkest neutral spot until your shadows look and measure neutral. Now you have set your shadow. Turn the Preview checkbox off and on to see what you have done to the image so far.