How to get TIFF file with 8 bit color depth

Hello. I am a GIMP user. My goal is to submit a TIFF file of the highest quality possible to Nations Photo Lab, for printing. The help page for Nations Photo Lab says that the file submitted must have 8 bit color depth. I have read conflicting reports about the color depth of files exported from GIMP. My question is: as a user of GIMP, what do I need to do in order to get a TIFF file of a picture which has 8 bit color depth? Thank you.

You may get a better answer, but I tried a couple of things with the following results. I think the format and properties of the image you’re starting with may be of importance.

I exported a PNG file with 8-bit color depth from GIMP as a TIFF file and the color depth of the TIFF was 8 bits. I imported an Encapsulated PostScript (EPS) file with 16 bit color depth and exported it as a TIFF and the latter had 8 bit color depth. I determined this by using the ImageMagick command `identify’. I didn’t have to do anything special.

I use ImageMagick for manipulating graphics files with command-line commands, partly because I haven’t yet learned the Python or Scheme interfaces to GIMP. I think it’s likely that you can specify the bit depth with ImageMagick’s ‘convert’ and ‘mogrify’ commands. However, it’s probably possible to do this with GIMP, too. I didn’t see any way of doing this from the menu that appears when exporting from GIMP, but maybe there’s a way of doing it. As mentioned, it wasn’t necessary for these two examples.

In GIMP check menu Image → Precision and check that it is set to 8-bit (and check that Image → Mode is RGB). Exporting to TIF should then result in 8-bit color depth.