Help in analysing PNG

[GIMP101]

GIMP Version: 2.8.22
Operating System: Windows
OS Version: Windows 10
GIMP Experience: New User

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Hello,

I hope somebody can help me!

I am trying to find a hidden image/data in a PNG.

As far as I can tell using GIMP, the image is single layer sRGB with no alpha channel.

A Compress Or Die 'heat map' of the image clearly shows a 'spiral' of high density non repeating 'data' over a localised section of the image; how would I find out exactly what this is?

EXIF/metadata fields are empty except for the comments section where there are six characters '<<6&FF' - could this relate to colour palette information in some way?


Any comments or help would be most appreciated.

Thanks

[sallyanne]

Are you able to upload the image?

[GIMP101]

Yes, of course I can.

But I would really like to try to 'solve' it myself first using GIMP as opposed to being given the answer by a super experienced GIMP user!

I can post a link to the image soon ...

[Nidhogg]

It relates to RGBA color model, the FF in the end is the alpha channel.

[GIMP101]

Thank you.

I will experiment with RGBA and see what happens ...

[ofnuts]

"<<" is the shift-left operator in C and other programming languages, so this could mean to shift 6 bits left and then keep the lower 8 bits (& FF). Shifting left is multiplying by 2⁶=64.

[GIMP101]

Thank you.

Yes, I was thinking that maybe the '<<' indicated a bitwise left shift operator but if so (and please correct me if I am wrong), I'm not sure how to go from there to three 8-bit numbers for RGB and then to use GIMP to display just the colour represented by those numbers ...

[Nidhogg]

Displaying all pixels sharing same color can be done from Menu: Select/By Color.
Drag the threshold slider to 0.0, and paint a small area with same color as your target color,
on which you will click with the color selection tool.
Searching specific colors in an image would be a cool plug-in. If it's already possible somehow I'd really like to know.