How to check if an image compressor is truly lossless ?

[adyga]

Hi all

I need some ideas on how do I check if my image is truly losslessly compressed ?

because I doing an archive of more than 2000 analog images, with 300dpi 600dpi and 1200dpi

I am currently using PNG.

I wanted to check if PNG is lossless in addition to JPEG2000LC.

help is greatly appreciated.

[spazmire11]

well i think a checksum generator would be usefull here basicly,

convert image to whatever format

convert the image back to the same format it was in

compare the two checksums

that might do it, however i realy see no point to it if you cant tell the diffrence

[adyga]

Thanks spazmire11 for your interest

well i think a checksum generator would be usefull here basicly,

I think its a great idea to begin with.

however i realy see no point to it if you cant tell the diffrence

maybe eye cant catch the difference but with a noisy little-grainy analog images and constant save and close it will lose some detail that might be usefull in the future, maybe to do a hologram of ancestors ?

[LLXX]

Save it as BMP, open that BMP and convert to PNG, then save that PNG as BMP (of same settings).

Now FC the two bitmap files and they should be byte-identical.

If I remember correctly, JPG at 100% is still slightly lossy due to the DCT process used.