Using digital cameras to grab textures from real life introduces a whole new set of problems. Let’s say you find a wonderfully filthy concrete wall in a dark parking garage, which would work perfectly in the gritty urban setting of your game, and want to take a picture. The problem is, that due to the lack of light (and a tripod), you need to use the flash. Knowing that the flash may cause bright flaring reflections if you take the picture facing the wall straight, you shoot at a slightly odd angle. While the results are now bright and crisp, there is still a very visible gradient-like highlight in the middle of the picture, reducing the usable area of the texture.

What many people would think to do in this situation, would be to:

• Create a selection with a gradient tool, and adjust the luminosity of the selected area, or
  
  
• Painstakingly Dodge the edges of the picture, until the overall luminosity of the texture is evened out

However, both these approaches mean a lot of work, and do not always provide perfect results unless you’re willing to spend hours.

This is where the High Pass filter comes in handy. Which is underrated by many 3d artists and today we will remove the flash highlights from our textures or digital photos using Filter > Other > High-Pass


Step 1: Open an effected image/texture, duplicate the image and apply a High Pass filter with a large radius on duplicate image. The rule of thumb is that the radius of the filter should be larger than any detail you want to preserve. Since in this case the detail to be removed (the highlight) is almost the size of the whole picture, feel free to use a radius well above 70. Note that the larger the radius, the longer it takes to process - just as with Gaussian Blur.


Step 2: As you can see, the High Pass filter not only reduces brightness differences, it also reduces the contrast of the image, paling the colors. Please choose Edit > Fade High Pass and select Luminosity in the mode. If you find the effect of the high pass filter too drastic, you can reduce its Opacity.


Step 3: Since a lot of contrast was lost in the process, finalize the picture by increasing the contrast (or adjusting the Levels, depending on the case) until it looks good, then Fade the contrast effect once more with Luminosity to retain the coloring of the original image. See the difference? Feel the difference of not having had to do extra work?


The same rules apply for so called detail textures (a fine example of them can be found in games that use the Unreal engine.) Since the very purpose of detail textures is to add small, sharp details to textures up close, they are obviously ideal targets for the High Pass filter. Because the details needed are indeed very small, feel free to use High Pass quite harshly with small radius values.