Vertical dither - PS tutorial (index colors)

[Darkcrafter07]

I made a quick tutorial for Photoshop on how to do a vertical dither pattern for Doom images. This might provide you with better compression ratios, both PNG and WAD as these favor horizontal and vertical lines of the same color. That also might make for a better artistic effect.

 

1) Duplicate your image twice;

2) On the first copy index colors without dithering;

3) On the second copy index colors with dithering pattern of your choice;

4) Subtract the second copy from the first one with "Normal" layer mixing mode. Copy the contents of the 2nd copy and paste it in the 1st one, invert the colors of the 2nd copy and set layer opacity to 50%. Merge the layers. You now get your pure dithering pattern. Downscale it with nearest neighbor algorithm by 50% vertically and upscale it by 200% back with the same nearest neighbor method;

5) Get 1st copy transparency and invert selection;

6) Using the resulting selection, clear the 2nd copy contents. That will prevent pixelized borders to leak in the 1st copy;

7) Invert 2nd copy image and use some high pass to make it totally neutral regarding affecting (non-affecting then) 1st copy brightness;

8) Merge layers with 2nd copy mixing mode set to "Linear Light"

9) Index colors without dithering.

 

 

Now there come some photoshop actions, necessary patterns and Doom palette file and PNGQuant with an easy to run batch script and details. Make sure it contains MS Windows exe file so your antivirus or browser may raise a false alert over that.

Darkcrafter07_PNGQuant_Doom.zip

Darkcrafter07_vertical_dither.zip

Edited April 7 by Darkcrafter07