The Formulas Rendering Plug-In for the GIMP 2 version 0.9.8
Released on 14-Nov-2010 at 16:00
Written by Nicolas BENOIT, nbenoit@tuxfamily.org
http://nbenoit.tuxfamily.org
French translation: Nicolas BENOIT
German translation: Dominik SEICHTER
This simple plugin allows you to change the values of each color channel of each pixel of a layer by using mathematical expressions.
It is compatible with RGB* and Gray* layers.
| Operator | Description |
| + | addition |
| - | substraction |
| * | multiplication |
| / | division |
| ^ | power |
| % | modulo |
| Function | Description | Number of arguments |
| red ( arg1, arg2 ) | Red channel value at (arg1,arg2) coordinates | two arguments |
| gray ( arg1, arg2 ) | Gray channel value at (arg1,arg2) coordinates | two arguments |
| green ( arg1, arg2 ) | Green channel value at (arg1,arg2) coordinates | two arguments |
| blue ( arg1, arg2 ) | Blue channel value at (arg1,arg2) coordinates | two arguments |
| alpha ( arg1, arg2 ) | Alpha channel value at (arg1,arg2) coordinates | two arguments |
| rgb ( arg1, arg2 ) | Currently processed channel value at (arg1,arg2) coordinates | two arguments |
| rand ( ) | random value between 0.0 and 1.0 | no argument |
| sin ( arg ) | sine function | one argument |
| sinh ( arg ) | hyperbolic sine function | one argument |
| asin ( arg ) | arc sine function | one argument |
| asinh( arg ) | arc hyperbolic sine function | one argument |
| cos ( arg ) | cosine function | one argument |
| cosh ( arg ) | hyperbolic cosine function | one argument |
| acos ( arg ) | arc cosine function | one argument |
| acosh ( arg ) | arc hyperbolic cosine function | one argument |
| tan ( arg ) | tangent function | one argument |
| tanh ( arg ) | hyperbolic tangent function | one argument |
| atan ( arg ) | arc tangent function | one argument |
| atan2 ( arg1, arg2 ) | arc tangent function returning the correct quadrant | two arguments |
| atanh ( arg ) | arc hyperbolic tangent function | one argument |
| rad ( arg ) | to radians conversion | one argument |
| deg ( arg ) | to degrees conversion | one argument |
| sqrt ( arg ) | square root function | one argument |
| cbrt ( arg ) | cube root function | one argument |
| log ( arg ) | natural logarithmic function | one argument |
| log2 ( arg ) | base-2 logarithmic function | one argument |
| log10 ( arg ) | base-10 logarithmic function | one argument |
| exp ( arg ) | base-e exponential function | one argument |
| abs ( arg ) | absolute value | one argument |
| sign ( arg ) | sign of the value | one argument |
| ceil ( arg ) | smallest integral value not less than argument | one argument |
| round ( arg ) | round to nearest integer, away from zero | one argument |
| min ( arg1, arg2, ..., argn ) | minimal value | one or more arguments |
| max ( arg1, arg2, ..., argn ) | maximal value | one or more arguments |
| avg ( arg1, arg2, ..., argn ) | average value | one or more arguments |
| Value | Description |
| pi | pi constant |
| e | e constant |
| j | gold number |
| w | width of the image |
| h | height of the image |
| x | x of the cartesian coordinate of the current pixel |
| y | y of the cartesian coordinate of the current pixel |
| r | r of the polar coordinate of the current pixel |
| t | t of the polar coordinate of the current pixel |
As you can see on the screenshot above, the interface of the plug-in is pretty simple.
You just have to enter the formulas inside the text fields...
Always keep in mind that the result of a formula must be between 0 and 255.
Here is another screenshot with an edge detection formula (Sobel filter) applied to a black G-clef on a white background.
Here are a few examples:
| Red Channel | Green Channel | Blue Channel | |
| 1 | 100 | (1+cos(rad(x*2.21*x/(y+1))))*92 | (1+sin(rad(x*2.21*x/(y+1))))*127 |
| 2 | sqrt((rgb(x+1,y-1)+2*rgb(x+1,y)+rgb(x+1,y+1)-rgb(x-1,y-1)-2*rgb(x-1,y)-rgb(x-1,y+1))^2+((rgb(x-1,y+1)+2*rgb(x,y+1)+rgb(x+1,y+1)-rgb(x-1,y-1)-2*rgb(x-1,y)-rgb(x-1,y+1))^2))*(255/1442.5) | sqrt((rgb(x+1,y-1)+2*rgb(x+1,y)+rgb(x+1,y+1)-rgb(x-1,y-1)-2*rgb(x-1,y)-rgb(x-1,y+1))^2+((rgb(x-1,y+1)+2*rgb(x,y+1)+rgb(x+1,y+1)-rgb(x-1,y-1)-2*rgb(x-1,y)-rgb(x-1,y+1))^2))*(255/1442.5) | sqrt((rgb(x+1,y-1)+2*rgb(x+1,y)+rgb(x+1,y+1)-rgb(x-1,y-1)-2*rgb(x-1,y)-rgb(x-1,y+1))^2+((rgb(x-1,y+1)+2*rgb(x,y+1)+rgb(x+1,y+1)-rgb(x-1,y-1)-2*rgb(x-1,y)-rgb(x-1,y+1))^2))*(255/1442.5) |
| 3 | ((1+cos(rad(x+y)))*127)+1 | ((1+sin(rad(x+y)))*127)+1 | y%255 |
| 4 | (1+sin(x/(w/pi)))*127 | (1+sin(y/(w/pi)))*127 | 255 |
| 5 | (sin(r)+1)*127 | (sin(r)+1)*64 | (sin(r+pi)+1)*127 |