Does uploading an indexed image still require an L8 conversion?

scottSD · ‎2019-11-08

I have a question about the new L8 image support.

I created an indexed image and noticed that in order for the image source file (located in TouchGFX\generated\images\src) to be created as an L8 with a clut table, I still need to choose L8_ARGB8888 as the "Image Format" in the TouchGFX Designer's Images tab as seen in the following article:

https://touchgfx.zendesk.com/hc/en-us/articles/360009793299-Using-the-L8-Image-Format

Should the image be a non-indexed ARGB888 (limited to 256 colors) and let the TouchGFX do the conversion?

If I add an indexed image, it looks like TouchGFX takes that indexed image and remaps it into an ARGB8888 prior to conversion. Is this how it works?

I also noticed that if DITHERING is enabled it will add colors to the point of it being more than the 256 maximum.

Also, is there a way for the source file to be created without TouchGFX doing this conversion?

Martin KJELDSEN · ‎2019-11-12

You _must_ ensure that your input image has less than 256 colors or (256 - DITHERING).

How did you see that input images are remapped to ARGB8888 prior to conversion? Could be true 🙂

scottSD · ‎2019-11-12

Martin,

Thanks for the reply. My question is basically "why do I need to select L8_ARGB8888 if the image is already indexed"?

I added an indexed image (created in GIMP as an indexed image). TouchGFX's "Image Format" is RGB888/ARGB8888 by Default. When I generate code, the image source file created is ARGB8888. I want L8. So, in order for it to be an L8_ARGB8888 indexed image, (which it originally was), I need to set Image Format as such and let TouchGFX convert it. It does not appear that TouchGFX leaves the image at it's native format.

Based on this behavior, I said "it looks" like it remaps it, but that was just a guess. Could it be true? 😉

Also, for the 256 colors (256 - DITHERING), I notice that this also includes any unique transparent colors in the image. These are added to the overall number of colors in the CLUT and further limiting the number colors.