Simple Range Adjustments - Adobe Photoshop

Create a gradient that goes from pure black to pure white to represent your bump map.

  1. Click the Gradient tool or press Shift+G until it cycles to the Gradient tool(instead of to the Paint Bucket tool).
  2. Create a new file(File > New) in the resolution of your choice and drag within the canvas to create a gradient. Make sure to choose a black and white gradient. It does not matter for this tutorial whether you are still in RGB or grayscale mode, nor if you go from black to white or vice versa. Just make sure that you have the full range of black, white, and grays in your image. Before you start adjusting the values, create a few markers to help keep track of the numbers. The Color Sampler tool allows you to set up to four markers.
  3. Your gradient is an example of a bump map that is difficult to adjust within the needed range.

    gradient is an example of a bump map that is difficult to adjust within the needed range

  4. Choose the Color Sampler tool from the toolbox by pressing I or choosing Shift+I.
  5. Make sure the Sample Size is 3×3 Average in the options bar and click a spot that shows up as 50 percent gray(or 128, 128, 128 in RGB settings).
  6. This is your 50 percent gray marker. This is the point that is flat, neither going up nor down.

    50 percent gray marker

    Don’t worry if your marker doesn’t hit the spot when you first lay it down. If you place the mouse pointer over the marker and it changes to a triangle, you can drag it to a better spot.

  7. Create a marker for the two extremes: the 0 percent and the 100 percent gray(black and white). Click what reads as pure white to set marker #2, then click pure black to set marker #3. This allows you to consistently track the changes you make.

Your markers don’t have to be in the same place as mine, but your values should read the same.

values should read the same

Say that your bump map is perfect, except that you can’t have the values go within the 10 percent range of either end of the grayscale. In other words, your bump map has to be within 10 percent and 90 percent gray. The general relation to itself is perfect as is. If you tried to paint out just the nine percent gray and below, for example, the overall bump map values would not have the same relationship, resulting in a flattening out at either end, The lower figure is the result of adjusting the bump to keep the relative relationship of the values.

How you adjust your bump map affects how it is rendered.

adjust your bump map affects how it is rendered.

What you really want is to squish the values that you have right now within 10 percent and 90 percent gray. Luckily, the solution is easy.

  1. Add a levels adjustment layer by going to Layer > New Adjustment Layer > Levels.
  2. Click OK to Accept the default settings and name in the New Layer dialog box.
  3. In the Levels dialog box, change the Output Level slider from 0–255 to 26–230. That’s roughly 10 percent of 255 and 90 percent of 255.
  4. Click OK and take a look at your gray level values by looking at the values of your color markers.

Bringing in the output range to be within the 10 percent and 90 percent range.

Bringing in the output range to be within the 10 percent and 90 percent range.

As you can see, your midgray(50 percent flat mark) is unaffected, but your extreme ends have been brought in between 10 percent and 90 percent. This simple method works as long as you bring in the range evenly on both sides.


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