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I'm making some pixel art in gimp and I so I figured I should use the indexed color mode since I won't be using very many colors.

About halfway through my project I realized that I wanted to be able to create layer groups because I want to be able to use tools like move, change perspective, and rotate on a group of layers - rather than on just one layer.

Apparently I can't create layer groups indexed mode. I understand that I can just revert to RGB mode, or even just link layers together - and I'll probably do that - but I'm just curious: why can't I create a layer group in indexed mode?

I've looked through the gimp manual and searched for tags here and I can't seem to find an answer.

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It is probably not satisfying, but the actual answer is:

You can't create a layer group in indexed mode because this has not been implemented in GIMP.

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In computing, indexed color is a technique to manage digital images' colors in a limited fashion, in order to save computer memory and file storage, while speeding up display refresh and file transfers. It is a form of vector quantization compression.

When an image is encoded in this way, color information is not directly carried by the image pixel data, but is stored in a separate piece of data called a palette: an array of color elements.

So you must change your image mode to RGB > Manage your Project as layered file > convert to indexed mode again (Flat Image).

RGB Mode GIMP

RGB- This is the default mode, used for high-quality images, and able to display millions of colors. This is also the mode for most of your image work including scaling, cropping, and even flipping. In RGB mode, each pixel consists of three different components: R->Red, G->Green, B->Blue. Each of these in turn can have an intensity value of 0-255. What you see at every pixel is an additive combination of these three components.

Indexed- This is the mode usually used when file size is of concern, or when you are working with images with few colors. It involves using a fixed number of colors (256 or less) for the entire image to represent colors. By default, when you change an image to a palleted image, GIMP generates an “optimum palette” to best represent your image.

I think There is no way to edit the file as layered in Indexed Mode.

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    Thank you so much for the detailed answer (!!) but I'm not sure it actually answers my question. I was asking "Why am I not able to create layer groups in indexed mode?" and not "How can I fix my problem?" -Though maybe I don't completely understand how layers and layer groups work. Does the fact that the indexed mode uses a special predetermined palette have to do with the fact that I can't create layer groups? If so then why am I able to create new layers in indexed mode? – Josie Thompson May 2 '15 at 23:07
  • At the first section I answer your Q @JosieThompson – Lunaticbrain May 2 '15 at 23:09
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    I still don't understand though: What does the color index have to do with the ability to create layer groups if a layer group is simply an object - that acts as a layer that can hold other layers? – Josie Thompson May 2 '15 at 23:17
  • @JosieThompson For more info Please visit en.wikipedia.org/wiki/Indexed_color – Lunaticbrain May 3 '15 at 16:35
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    Explaining how indexed color works does not answer this question. The answer is rather like "layer groups in indexed files (or indexing files with layer groups) have not been implemented in GIMP". But for specifics, it would be best to ask on the gimp developer mailing list. – Michael Schumacher May 4 '15 at 11:59
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i believe you can't create groups/folder of layers because a design decision from Gimp community, perhaps to mantain it simple. as each layer can also mean an animation frame on a gif image.

  • Your answer is similar to the answer of @michael-schumacher. Can you please explain better the difference? Welcome to GD.SE! – Mensch Sep 13 '15 at 23:23
  • Where is the rationale behind this design decision publicly documented? – Damian Yerrick Aug 15 '17 at 15:56
  • There is none, people like to make up stuff like that. – Michael Schumacher Sep 30 '17 at 17:36

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