4 bpp textures offset left by 1 pixel

[tiddlets]

I'm trying to modify some 4bpp paletted textures for Starship, but the resulting textures are offset one pixel to the left, even when loading an unmodified exported PNG. This doesn't seem to happen with RGBA images.

You can see this in Retro 0.2.0 after using Create OTR/O2R, then Replace Textures to dump out sf64.o2r as PNGs. If you then go to Debug, Textures, Select Texture File and pick the unmodified sf64/ast_common/aXTex.png (for example), set the drop down to Palette4bpp, then Convert Texture, you will see the image offset one pixel to the left compared with viewing the PNG directly, with a black bar on the right where the last column of pixels is replaced by a column of palette index 0. (Interestingly, the same occurs when selecting Grayscale4bpp, but not with Grayscale8bpp.)

The same off-by-one results occur when creating an O2R and loading it with Starship - always by one pixel, even when increasing the texture size. I tried this with 0.0.5 for comparison and had the same results.