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+---- Thread: How to iterate pixels with python API? (/Thread-How-to-iterate-pixels-with-python-API)
How to iterate pixels with python API? - Scallact - 06-29-2026
Hi,
[GIMP 3.2 python API]
I'm trying to iterate over all the coordinates of an image, and create some calculated pixel values on a new layer.
I'm currently using the Gimp.Drawable.set_pixel() method, but its very slow (and supposed to be).
I'm struggling to find the right way to do this. I think there was a concept called "regions" in GIMP 2.xx. I understand I have to use a Gegl.Buffer. But from there I'm stuck
I can't find any definition, or just circular definitions, of what a Gegl buffer is, or any other concept. That's what makes things really difficult.
Does a "buffer" represent the whole drawable? And if it is, how do I extract just a tile and iterate over the pixels?
What is a "shadow buffer"?
What is a "handler"?
What is "the abyss"?
Thanks!
RE: How to iterate pixels with python API? - Scallact - 07-02-2026
I was finally able to crack this problem. Here is some sample code:
Code:
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# your standard imports, don't forget Gegl
import gi
gi.require_version('Gimp', '3.0')
from gi.repository import Gimp
gi.require_version('GimpUi', '3.0')
from gi.repository import GimpUi
gi.require_version('Gegl', '0.4')
from gi.repository import Gegl # << Gegl needed
# [...] other imports [...]
# needed for this example
import random
#
# [...] some code [...]
#
def randomColors(layer) :
# example on how to iterate over pixels with Gegl and apply these in batches
# this is much faster than drawing one by one with Gimp.Drawable.set_pixel()
# important : the changed pixels can't be undone, it's better to draw them on a new layer
thisBuffer = layer.get_buffer()
startx = 100
starty = 100
sizex = 80 # region size, preferably not too big, iterate if necessary
sizey = 80
rectangleRegion = Gegl.Rectangle.new(startx, starty, sizex, sizey)
bufferSize = sizex * sizey
bufferData = []
i = 0
while i < bufferSize :
# attribute some random values to rgb
r = random.randint(0,255)
g = random.randint(0,255)
b = random.randint(0,255)
bufferData.extend([r, g, b])
i += 1
thisBuffer.set(rectangleRegion, "RGB u8", bufferData) # << this is where we write pixels!
layer.update(startx, starty, sizex, sizey) # << necessary refresh
RE: How to iterate pixels with python API? - Scallact - 07-09-2026
Just a little Post-Scriptum about the Babl pixel format in the .set_rectangle method.
Here are the formats that I could gather from the internet, notably from here:
- u... are for integer
- RGB are for linear values
- R'G'B' are for non-linear values (ie, with a perceptual color profile)
- A is always linear
The formats:
- RGB u8
- RGBA u8
- RGBA float
- R'G'B' u8
- R'G'B'A u8
- R'G'B'A float
The formats I presume should logically exist (correct me if wrong):
- RGB u16
- RGBA u16
- R'G'B' u16
- R'G'B'A u16
- RGB u32
- RGBA u32
- R'G'B' u32
- R'G'B'A u32
- RGB float
- R'G'B' float
RE: How to iterate pixels with python API? - CmykStudent_ - 07-09-2026
Scallact: For reference, all babl formats can be found here: https://gegl.org/babl/Reference.html
RE: How to iterate pixels with python API? - Scallact - 07-09-2026
(07-09-2026, 07:44 PM)CmykStudent_ Wrote: Scallact: For reference, all babl formats can be found here: https://gegl.org/babl/Reference.html
Oh wow, there a lot!!! That's crazy!
Thanks a lot, I should have found that myself! But Gogl doesn't seem to like Gegl! ;-) (Just joking)