JPG and profil include in the EXIFS : why ?

[Fabien]

When I load a JPG into GIMP and use it, GIMP writes a profile to the EXIFs.

What's the point of this, given that a profile is only used to adjust the colourimetry errors of a device (screen, printer, etc.)?

[Ofnuts]

(03-05-2024, 04:51 PM)Fabien Wrote: When I load a JPG into GIMP and use it, GIMP writes a profile to the EXIFs.

What's the point of this, given that a profile is only used to adjust the colourimetry errors of a device (screen, printer, etc.)?

Wrong assumption. The profile maps an encoding to real world values. So the encoding in the image, together with the image color profile, tells what the real word values should be, and these real world values, together with the display/printer color profile are used to compute inputs to the display/printer so that it outputs the originally intended real world values.  

It happens that in many Images the color profile is sRGB and that if not specified SRGB is used by default, but this is not mandatory and can be something else (AdobeRGB is another frequent one, that supports a wider range of colors (aka "gamut")).

[Fabien]

Thank you for your reply,

I misspoke...
Experiment:
1) I take a photo with my reflex then I load it on the desktop of my win11 PC.

I look at the EXIFs (complete) and I don't see any profile.

2) I load this last photo into GIMP and immediately export this image without any processing.
I look at the EXIFs (complete) and I still don't see a saved profile.

3) I do the same thing as before, but I do some work: light, contrast, colour etc...
I export and look at the EXIFs... This time, a profile is recorded in the EXIFs of the JPG file...

So...

Normally a profile 'which of course depends on the sRGB or RGB colour space,
is stored in the PC and used to correct display errors on a screen (in the case of a screen peripheral).

So why include a profile in the EXIFs of a JPG image?

[Tas_mania]

When I export JPEGS from Gimp I see this box:

   

[PixLab]

(03-05-2024, 09:34 PM)Tas_mania Wrote: When I export JPEGS from Gimp I see this box:

Indeed it's an option, OP just have to uncheck this option...

[Fabien]

Thank you for your time.
Obviously, I had seen that; but my question is why because a profile is associated with a particular device and is not universal... so why insert 1 profile and for which device and what happens if I load this photo on another different device?

[PixLab]

(03-06-2024, 09:09 AM)Fabien Wrote: Thank you for your time.
Obviously, I had seen that; but my question is why because a profile is associated with a particular device and is not universal... so why insert 1 profile and for which device and what happens if I load this photo on another different device?

Ofnuts explained it quite well in my opinion,

Ofnuts Wrote:together with the display/printer color profile are used to compute inputs to the display/printer so that it outputs the originally intended real world values.

In a more simple words, when the profile is embedded, if you put that picture on another computer or send to a printer which don't have the same icc color profile, it will show the picture with the right color that you saw on the previous monitor from another device BECAUSE the new computer read the embedded color profile and adapt to it... (I hope it is simple enough explanation to understand without discording facts)

[Fabien]

I'm really sorry to contradict you... A profile is used to correct "technical" display or printing, faults.
Let's take a screen as an example.

The screen manufacturer, or the result of a screen calibration, is associated with the equipment concerned: in this case a screen.
(If we had several screens of different types, there would be another profile specific to this one).

This profile is saved IN the PC; so that all the images that arrive on that PC, are displayed correctly on the screen.

second example :
I want to print an image... the PC (it software) will use another profile, this one, specific to printers (subtractive synthesis).
As you can see, a profile cannot normally be integrated into an image...

By the way, find these profiles in your PC; they are stored there.

[Ofnuts]

(03-06-2024, 02:30 PM)Fabien Wrote: I'm really sorry to contradict you... A profile is used to correct "technical" display or printing, faults.
Let's take a screen as an example.

The screen manufacturer, or the result of a screen calibration, is associated with the equipment concerned: in this case a screen.
(If we had several screens of different types, there would be another profile specific to this one).

This profile is saved IN the PC; so that all the images that arrive on that PC, are displayed correctly on the screen.

second example :
I want to print an image... the PC (it software) will use another profile, this one, specific to printers (subtractive synthesis).
As you can see, a profile cannot normally be integrated into an image...

By the way, find these profiles in your PC; they are stored there.

The image profile and the display/print profile are composed to create an output that matches the intended color of the image on the target output device.

If everybody used the same image profile there would be no image profile since it could be baked  in the image apps (and this is more or less what happens for sRGB). However the designers of image formats have kept the possibility to use a different image profile, and it's all the better. For instance I can ask my camera to encode Jpegs with the AdobeRGB color profile, that allows a greater color range/gamut in the image (but requires very good displays and printers to be useful).

[Fabien]

I think I understand the origin of our difference: the word profile is used several times for different things.

There is indeed an sRGB RGB or other profile written in the JPG file, and which describes the colour space used by the system that created or modified this photo before it arrived on the PC; but the name profile is also given to the correction file located in the PC and which is used to correct the fact that, technically, screens don't generally display exactly the right colours.
This file only concerns the screen used on the 'final' PC in this case.