Desaturating: Tolerable on Occasion - Adobe Photoshop

The common way of making a bump map is to convert it to grayscale.

  1. Open the brick wall color texture map Brick.tga.
  2. Go to the menu bar and choose Image > Adjustments > Desaturate or press Shift+Command+U (Win: Shift+Ctrl+U).
  3. This is how your brick tile looks with standard desaturation.

    how your brick tile looks with standard desaturation

    This won’t do for a bump map, especially since by standard conventions of the way a bump map is processed the mortar will be sticking out and the bricks will be sinking in. The Lighter using your maps may be able to reverse the effect, but again by convention, you should invert it.

  4. To invert your image press Command+I(Win:Ctrl+I) or go to Image > Adjustments > Invert.
  5. The map is inverted, so the mortar goes in and the brick is raised

    map is inverted, so the mortar goes in and the brick is raised

Does it work? Yes, it works. That’s why so many people stop here—but look at the image values.You need to set up your Info palette options to show HSB.

  1. Go to the drop-down menu in the Info palette and choose Info Options.
  2. Change the Second Color Readout Mode from CMYK to HSB Color and click OK.
  3. Press I to choose the Eyedropper tool, make sure your Info palette is visible, and take a look at the mortar.

If you hover or slide the tool over mortar areas you see that the values displayed in the Info palette under the B section of the HSB area are all under the 50 percent mark, averaging around 30 percent brightness according to my guesstimation. Now take a look at the brick. The values are averaging 55 percent brightness. One brick is even around 47 percent and is therefore displaced inward.

Many would ignore the numbers, clean this up, and turn it in. This renders decently on a sample. The problem may arise, however, that this texture butts up to another texture and any difference in values between the two maps are obvious.

In other words, too often this method of just desaturating does not work. f objects are supposed to be flush to your displaced texture, then the values in the bump map you just created will not work; if the brick wall has to look photorealistic and a camera will be close or focusing on it, the bump map you just created will not work. Each of these sample situations calls for a more sophisticated grayscale bump/ displacement map.

Channel Mixer: A Better Way

I really like using- this method to create a bump map. It lets me interactively blend all three channels to get the type of grayscale I want. Start with the same brick color map.

Make a coordinating bump map

coordinating bump map

  1. Go to Layer > New Adjustment Layer > hannel Mixer.
  2. Alternatively, you can go to the bottom of the Layers palette and access the adjustment layer there. You could go to the Image menu, but that restricts your ability to go back and edit at a later date.

    Creating a Channel Mixer layer from the menu bar or from the Layers palette are both equally valid

    Channel Mixer layer from the menu bar or from the Layers palette are both equally valid

  3. Click OK to accept the name and default settings in the New Layer dialog box. The Channel Mixer dialog box appears, using RGB mode by default.
  4. Go to the bottom of the dialog box and select the Monochrome checkbox to display the layer in grayscale. The output channel at the top of the dialog box reflects the change by switching to Gray. You can play with the sliders to get the look you want.
  5. Use the Eyedropper tool to check your values as you do your adjusting. Hover the tool over an area and look at the HSB B value in the Info palette for feedback.
  6. Setting negative values in the Channel Mixer’s source channels seems to subtract its values from the composite, but does not invert.(You can’t invert a channel using this.) Once I had the basic look that I wanted, the Eyedropper info indicated the values were a little too dark overall, so I increased the constant by 15.

    You don’t need to use the same values I have here. You do want to make sure your mortar is darker than your bricks and that no highlight /bump in the mortar is higher than the brick value levels.

    Channel mixer

  7. Click OK to accept your settings; take a look.

Beyond ease and control, look at the quality. Compare the results of the two different methods of grayscaling. You can see that in that the right image is superior in that the bricks are more even and the dirt/grime coloration incorporated into he left figure has been greatly reduced. Also, if you look in the mortar area, white spots would have jutted out far beyond the level of the bricks in the left image. This is no longer an issue with the image on the right created with the channel mixer.

The bump map you made in the previous section on the left and, on the right, the result of channel mixing.

previous section on the left and, on the right, the result of channel mixing

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