Neutralizing a Color Cast - Adobe Photoshop

In this example, the VFX supervisor originally asked you to paint the image with a blue cast to match the color-corrected plates received from the client. Once you were done, he thought it was perfect. Despite that, the client doesn’t like the blue cast that the movie has been working with and is trying to eradicate it. Rather than starting over from a neutralized plate, can you work with your painting and just get rid of the cast?

Of course you are wincing inside, thinking of how hue shifting causes all kinds of unwanted colorations, how putting in an overlay or doing too much image processing flattens the image’s color range; a litany of hurdles bombard your mind. Then you smile and say “Okay.”You remembered this particular chapter! I think this would be called grandiose delusions on my part, but if this chapter happens to save any of you, e-mail me and tell me the tale!

Placing Markers

Before neutralizing a color cast, find out exactly from where the cast is coming. Placing color markers aids your quest and gives you feedback during the process.

  1. Download file CC01.psd from this book’s companion web site and open it.
  2. Your original painting with a heavy blue cast.

  3. Click the lower-right triangle in the Eyedropper tool in the toolbox. From the pull-down menu, choosethe Color Sampler tool.
  4. The Color Sampler tool is hidden behind the Eyedropper tool.

  5. In the options bar shown in Figure, choose either 3 by 3 or 5 by 5 Average as the Sample Size setting.For this example I choose 3 by 3. Averaging between a few pixels ensures that you don’t get an off.
  6. Setting the Color Sampler options to an average gives you a more accurate reading.

  7. Find the brightest white point of your painting and click it with your Color Sampler tool.
  8. You see #1 with the average valuelisted in RGB in the Info palette, shown in Figure. (Choose Window > Show Info if you don’t have the Info palette up already.) You see the sampler symbol with a1 next to it, indicating from where the sample is being drawn. If you think you need to nudge it over just a bit, just place your cursor over it.When it changes into triangle, click and drag it to where you want it.

    The Info window with one color sampler marker.

  9. Choose the darkest black area of your image with the Color Sampler tool.

The Info palette displays this as #2.

With both the #1 sample and #2 sample, the red, green, and blue channels should have a different value from each other. That is causing a color cast.

If you have a sudden memory lapse and forget what area you sampled, have no fear Photoshop leaves the markers onscreen, with numbers indicating which sample i which. To clear the markers, go to the options bar and click the clear button. Figure shows the numbered markers. Now that the markers are set, you are ready to take the first step in neutralizing the color cast.

The Color Sampler leaves markers so you know where you are getting your values from.

Neutralizing Highlights

With your color markers set, first work on neutralizing your highlights. Take the neutralizing solution and spread it evenly over your head. Uh, wait. That’s from my hair-streaking kit. Now you know the answer to “Does she or doesn’t she?” As I recover from my utter embarrassment, take a look at the brightest points on your image as you subtract the color cast from the highlights.

  1. Add a Curves Adjustment layer to your document by clicking Layer > New Adjustment Layer > Curves.
  2. In this case it is imperative that you use a Curves Adjustment layer instead of the Image Adjustment Curves.

    Another way to do this: Go to the bottom of the Layers menu and choose Curves. See Figure for what this looks like. Either gives you the same result on a separate layer. You need the flexibility of the separate layer for going back to tweak the settings.

    You have multiple ways of doing the same thing. Click the Create New Fill or Adjustment Layer button on the bottom of the Layers palette.

  3. Name your new layer any name you wish and click OK. The Curves dialog box appears.
  4. Take a look at the values in your color sample #1 in the Info palette. Notice the highest value. In this case it is the blue channel with a value of 249.

  5. From the channel choices in the Curves dialog box, choose the channel that had the lowest value. In this example, shown in Figure, it’s red with a value of 241.
  6. You switch your curve editor to the channel with the lowest value.

  7. Click the curve’s upper-right node and nudge it to the left until the red value matches the highest value for the highlights—blue in this case.
  8. When you opened the curve editor, the sample colors were updated with a slash that divides the current and the corrected colors.

  9. Correct the green channel to match, using the same methods. The highlight cast has been neutralized.
  10. You are doing the same thing to the green channel.

You have neutralized the highlights, but your image is still unbalanced until you at least neutralize the shadows. Keep working through the next section.

Neutralizing Shadows

Before you leave the Curves dialog box, neutralize the shadows using the same method, but matching down to the lowest value.

  1. Take a look at color marker #2 and find the lowest value (in this case the red channel’s value of 72).
  2. Adjust the blue and green channel values by moving the lower-left node to the right and bringing down the values, as you see in Figure.
  3. The lower-left node represents the dark shadows. You may have to make some extreme adjustments, but trust in the numbers.

  4. Once you have neutralized your shadows, click OK to close the Curves dialog box, and look at your image so far.See Figure for an example of what your image should look like.Take a good look at the paths running through the land in Figure. See how they are tinged with green? That’s because you haven’t yet neutralized the midtones.
  5. Your image so far with highlights and shadows neutralized.

Choosing Midtones

The midtones are a bit trickier. Ideally, there exists a point on the image that is supposed to be 50 percent gray. In reality, that is rarely the case, and you need to determine your midpoint gray.

  1. Determine what a midtone point is and choose it with your color sampler for a #3 choice.
  2. Either add another curve layer or use the same one you’ve been using for the other adjustments.
  3. Grab the center of the line to curve the values up or down. Pulling up raises the value and pulling down lowers it, which you can see in Figure.
  4. I added another curve layer for clarity, but you could have made the adjustment on the existing Curve Adjustment layer.

Evening the Light

This image is looking much better, but you still need to even out the light.

  1. Go to the bottom of the Layers palette and click on the New Fill or Adjustment Layer button.
  2. In the pop-up menu, choose Levels like you see in Figure.
  3. Instead of adding the Levels Adjustment layer through the Layers palette, you could go to Layer > New Adjustment Layer > Levels

    In the Levels Dialog box, notice that the histogram is not spread across the entire range of values.

  4. Drag the end triangles to encompass the available levels represented in the graph; this expands the image’s tonal range. Figure shows this step.
  5. Drag the end triangles in, toward the range of the histogram, to set a new range for the image

  6. Click OK to accept your levels change.

Desaturating

Take a look at the image. All this processing has left it too saturated. The last order of business is to desaturate the image a bit.

  1. Add a Hue/Saturation Adjustment layer by going to Layer > New Adjustment Layer > Hue/Saturation, shown in Figure.
  2. You’re almost there!

  3. Accept the default name in the New Layer dialog box and take a look at the Hue/Saturation dialog box.
  4. Lower your saturation slowly by dragging the saturation slider to the left.Watch your histogram as you lower the saturation. The histogram, shown in Figure, fills in a bit and shows a fuller range overall.
  5. As you start to desaturate, the histogram fills in, reflecting a richer range in the image.

  6. When you have something that you are satisfied with, click OK.Now you have a properly neutralized image! Figures show the before and after.
  7. The before image.

    And the after image.


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