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

[TheInstinct]

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.