Forensic Photoshop Tutorial - Custom Filters Explained | PhotoshopSupport.com - The Diigo Meta page

• 25 Feb 08
  

  Jason Bao

  photoshop

  • The rules:

     
     
    • The scale should usually be equal to the sum of all the weights. 
    • If the sum of the weights divided by the scale is 1, then the offset should be 0. 
    • If the sum of the weights is 0 then the offset should be 128. 
    • If the sum of the weights divided by the scale is -1 then the offset should be 255. The image will be inverted from what it would be if the sum were +1. 
    • The sum of the weights divided by the scale should generally not be more than +1 or less than -1. Otherwise the image will come out very dark or very bright. 
    • The scale can't be less than 1 (you can't divide by zero). 
    • If the filtered image is very dark, the scale is probably too high. If it's very light, the scale is probably too low.

    • The way the custom plugin works is that the brightness value of a pixel in the image is multiplied by the number in the center form of the grid. Then the values for the surrounding pixels are determined by the values of the forms surrounding the center form. Everything is divided by the scale value and finally the offset number to get to the new brightness. This process is repeated for every pixel in the image.
    Add Sticky Note

Public Stiky Notes

• 
  Jason Bao on 2008-02-25
  The way the custom plugin works is that the brightness value of a pixel in the image is multiplied by the number in the center form of the grid. Then the values for the surrounding pixels are determined by the values of the forms surrounding the center form. Everything is divided by the scale value and finally the offset number to get to the new brightness. This process is repeated for every pixel in the image.

Would you like to comment?

Join Diigo for a free account, or sign in if you are already a member.