Jpeg unreadable

[Thierry]

Good morning,

I have a general technical question: is it possible that a photo, processed in "grayscale" mode, then exported in jpeg format, is unreadable afterwards?
Indeed, a person to whom I sent a photo, informs me that his computer can not open it, and tells him: "invalid ICC profile". Does the jpeg embed the ICC profile? or does the problem come from processing in "grayscale" mode and not in RGB?

Thank you in advance. 
Thierry

[rich2005]

A jpeg can certainly have a color profile, it does not need to be RGB or Grayscale, it can be say CMYK from some other application.

In Gimp setting the mode, Image -> Mode -> Grayscale and exporting gives options to save the color profile. Edit: Maybe untick that option for your file export.

You can of course Desaturate a RGB image to give gray and export as an RGB image.

It might be an MacOS thing, I do not know. If you can get ImageMagick https://imagemagick.org/script/download.php installed the command line magick identify -verbose filename.jpg can give lots of info and clues.

EDIT: As an example. With Gimp jpeg export and "Save color profile"
ImageMagick gives this
Compression: JPEG
 Quality: 90
 Orientation: Undefined
 Profiles:
   Profile-icc: 544 bytes
 Properties:
   date:create: 2024-04-12T18:39:48+00:00
   date:modify: 2024-04-12T18:39:48+00:00
   date:timestamp: 2024-04-12T18:42:26+00:00
   icc:copyright: Public Domain
   icc:description: GIMP built-in D65 Grayscale with sRGB TRC
   icc:manufacturer: GIMP
   icc:model: D65 Grayscale with sRGB TRC
   jpeg:colorspace: 1
   jpeg:  sampling-factor: 1x1

[Ofnuts]

(04-12-2024, 03:14 PM)Thierry Wrote: Good morning,

I have a general technical question: is it possible that a photo, processed in "grayscale" mode, then exported in jpeg format, is unreadable afterwards?
Indeed, a person to whom I sent a photo, informs me that his computer can not open it, and tells him: "invalid ICC profile". Does the jpeg embed the ICC profile? or does the problem come from processing in "grayscale" mode and not in RGB?

Thank you in advance. 
Thierry

Hard to tell without looking at the actual file actual. 

A first thing to do is to ask the person to send it back to you, and see if you get the same file (just in case it has been truncated or worse, re-encoded along the way).

Otherwise, there are corners of the JPEG standard that aren't always well supported. A well know case is the "Progressive" mode (that was a default with Gimp) still not suppoted by picture frames despite having been in the standard for 15 years. Here it could be JPEG with only the Luminosity channel. As recommended by others, if you replace it by a RGB image where R=G=B it will look more like a regular JPEG, and the way JPEGs are encoded the file size won't be much different since the two chroma channels, being uniform, will be compressed to near oblivion.