Gimp-Forum.net
Gimp 3: get indexed of each pixel from a layer = img.layers[0] pdb.gimp_layer - Printable Version

+- Gimp-Forum.net (https://www.gimp-forum.net)
+-- Forum: GIMP (https://www.gimp-forum.net/Forum-GIMP)
+--- Forum: Extending the GIMP (https://www.gimp-forum.net/Forum-Extending-the-GIMP)
+--- Thread: Gimp 3: get indexed of each pixel from a layer = img.layers[0] pdb.gimp_layer (/Thread-Gimp-3-get-indexed-of-each-pixel-from-a-layer-img-layers-0-pdb-gimp-layer)

Gimp 3: get indexed of each pixel from a layer = img.layers[0] pdb.gimp_layer - TheInstinct - 04-04-2025

Hi everybody,

I'm facing a serious problem when porting a plugin I wrote in Gimp 2.10 to Gimp 3.0 in python.

In Gimp 2, I used the following way to the color index of each pixel. It works very well:
Code:
layer = img.layers[0]
region = layer.get_pixel_rgn(0, 0, img.width, img.height, False, False)
pixels = array("B", region[0:img.width, 0:img.height])
pixels contains the index of the color [0;255] which is a byte.

In Gimp 3, you can get access to color information of the layer by using layer.get_buffer(...) but you won't get the color index as you must provide a Babl format. So you will get a color, or luminance in the format you selected "RGB u8" for example, but you won't get the indexes of the colors used by each pixel.

I made research but can't find how to get color index of each pixel. I hope some of you will be able to help me.

Thank you in advance for your support.

RE: Gimp 3: get indexed of each pixel from a layer = img.layers[0] pdb.gimp_layer - Ofnuts - 04-05-2025

(04-04-2025, 09:09 PM)TheInstinct Wrote: Hi everybody,

I'm facing a serious problem when porting a plugin I wrote in Gimp 2.10 to Gimp 3.0 in python.

In Gimp 2, I used the following way to the color index of each pixel. It works very well:
Code:
layer = img.layers[0]
region = layer.get_pixel_rgn(0, 0, img.width, img.height, False, False)
pixels = array("B", region[0:img.width, 0:img.height])
pixels contains the index of the color [0;255] which is a byte.

In Gimp 3, you can get access to color information of the layer by using layer.get_buffer(...) but you won't get the color index as you must provide a Babl format. So you will get a color, or luminance in the format you selected "RGB u8" for example, but you won't get the indexes of the colors used by each pixel.

I made research but can't find how to get color index of each pixel. I hope some of you will be able to help me.

Thank you in advance for your support.

Can you show you current Gimp3 code?

RE: Gimp 3: get indexed of each pixel from a layer = img.layers[0] pdb.gimp_layer - programmer_ceds - 04-05-2025

(04-04-2025, 09:09 PM)TheInstinct Wrote: Hi everybody,

I'm facing a serious problem when porting a plugin I wrote in Gimp 2.10 to Gimp 3.0 in python.

In Gimp 2, I used the following way to the color index of each pixel. It works very well:
Code:
layer = img.layers[0]
region = layer.get_pixel_rgn(0, 0, img.width, img.height, False, False)
pixels = array("B", region[0:img.width, 0:img.height])
pixels contains the index of the color [0;255] which is a byte.

In Gimp 3, you can get access to color information of the layer by using layer.get_buffer(...) but you won't get the color index as you must provide a Babl format. So you will get a color, or luminance in the format you selected "RGB u8" for example, but you won't get the indexes of the colors used by each pixel.

I made research but can't find how to get color index of each pixel. I hope some of you will be able to help me.

Thank you in advance for your support.

The following works for me when checking for transparent bytes - adjust src_offset to 0 for the red index, 1, 2 or 4 for green (depending on the bytes per pixel) etc.:
Code:
       buffer = drawable.get_buffer()

       rect = Gegl.Rectangle.new(0, 0, width, height)
       src_pixels = buffer.get(rect, 1.0, None, Gegl.AbyssPolicy.CLAMP)

       def Pixel_Is_Opaque (x, y):
           byte_opaque = False
           if (x >= 0) and (x < width) and (y >= 0) and (y < height):
               temp = ((y * width) + x) * bytes_per_pixel
               temp += src_index
               byte_opaque = True          # assume opaque
               for i in range (num_bytes_to_check) :
                   if check_pattern[i] != src_pixels[temp + i] :
                       byte_opaque = False
           return byte_opaque;

where src_index is set depending on the bytes per pixel:

Code:
       if (image_precision >= Gimp.Precision.U8_LINEAR) and (image_precision <= Gimp.Precision.U8_PERCEPTUAL) :
           src_index = 3
           check_pattern = [255]
       elif (image_precision >= Gimp.Precision.U16_LINEAR) and (image_precision <= Gimp.Precision.U16_PERCEPTUAL) :
           src_index = 6
           check_pattern = [255, 255]
       elif (image_precision >= Gimp.Precision.U32_LINEAR) and (image_precision <= Gimp.Precision.U32_PERCEPTUAL) :
           src_index = 12
           check_pattern = [255, 255, 255, 255]
       elif (image_precision >= Gimp.Precision.HALF_LINEAR) and (image_precision <= Gimp.Precision.HALF_PERCEPTUAL) :
           src_index = 6
           check_pattern = [0, 60]
       elif (image_precision >= Gimp.Precision.FLOAT_LINEAR) and (image_precision <= Gimp.Precision.FLOAT_PERCEPTUAL) :
           src_index = 12
           check_pattern = [0, 0, 128, 63]
       else :
           proc   = Gimp.get_pdb().lookup_procedure('gimp-message')
           proc_config = proc.create_config()
           proc_config.set_property('message', 'Unrecognised precision (bit depth)' +
                                        "\n" + "\n" + 'Execution terminated.')
           result = proc.run(proc_config)
           return


RE: Gimp 3: get indexed of each pixel from a layer = img.layers[0] pdb.gimp_layer - TheInstinct - 04-05-2025

Guys,

Thank you for studying my request. I undertstand I was not clear enough. It's my fault.

As I said, I'm in a context of an INDEXED image. It means that I have a palette of a predefined number of colors, let's say 256 (which is the maximum for an indexed image) and each pixel is assigned a value in a single byte which does refer to the color in position x in the palette. So one pixel = one byte.

Here in an example with a palette of 3 colors in RGB:
palette_color[0] = [0, 0, 255] <-- blue
palette_color[1] = [255, 0, 0] <--- red
palette_color[2] = [0, 255, 0] <-- green

Let's look at the 5 first pixels of the image: one byte per pixel
pixel[0]=1 <--red
pixel[1]=0 <-- blue
pixel[2]=0 <-- blue
pixel[3]=2 <-- green
pixel[4]=1 <-- red
.....

I use the following code to get access to the layer data. 
Code:
layer=img.get_layers()[0]
buffer=layer.get_buffer()
rect = Gegl.Rectangle.new(0, 0, layer.get_width(), layer.get_height())
data = buffer.get(rect, 1.0, "R~G~B~ u8", Gegl.AbyssPolicy.NONE)

I must use a Babl format. Here it is "R~G~B~ u8" so 1 byte for Red, one other for Green and another one for Blue here in sRGB. It's what I get in data but it's not what I want as I want the index of the color in the palette of colors.

There's no Babl format to get the color index of a pixel. So my question is the follwoing: is there another way than using get_buffer to get access to the data of the layer  ? In fact I'd like to get access to the raw_data of the layer which should contains the conlor_index as it was in Gimp 2.

I hope it clarifies.

RE: Gimp 3: get indexed of each pixel from a layer = img.layers[0] pdb.gimp_layer - Ofnuts - 04-06-2025

No time to dig in more but the Babl source code has multiple reference to palette, and even a 990-lines babl-palette.c source file so the functionality is probably there. But the format is probably the format of the palette entries, getting  palette indices could be something different.

RE: Gimp 3: get indexed of each pixel from a layer = img.layers[0] pdb.gimp_layer - teapot - 04-06-2025

Hi TheInstinct,

In setting the format name to "R~G~B~ u8" you are asking for it to store the data in that format.
Set the format name to None and the format of the buffer will be used.
So change to:
data = buffer.get(rect, 1.0, None, Gegl.AbyssPolicy.NONE)

I have just tested this on an indexed image with a 6x6 layer and I am getting the color indexes.

Printing the data, your format name gave:
b'\xec\x00\x00H\xa6\xf00\x84\\\xdc\x1d\xda\xf0\xe8H\xc4DH'
With format name None on the same layer I got:
b'\x00\x04\x03\x01\x05\x02'
and the colour indexes match the palette I used.

RE: Gimp 3: get indexed of each pixel from a layer = img.layers[0] pdb.gimp_layer - TheInstinct - 04-06-2025

teapot...... I love you. I had no idea we were able to provide 'None' instead of a string for this argument. You made my day. I just tested and it works like a charm.

Why isn't it documented? It should be.

Thank you very much to the community for this big help. Top

Note: I tested buffer.set and this one does not work the same. You can't set it to "" or None. You have to specify a valid Babl format. To me it's not consistant.