"Magic" extra bytes

M
Posted By
MervJones
Sep 17, 2003
Views
302
Replies
3
Status
Closed
Using PS 7 with Nikon Coolpix 5700
When doing a Photoshoot where I need to take several pictures quickly, I tend to shoot in High JPEG, max size. This gives me a large enough photo of a high enough quality to get decent prints. I then burn the originals from the CF card to CD and then copy them to my hard drive, usually to a folder called "xxxx orig" I then make whatever adjustments that I feel the photo warrents, then click "Save as" I then save the file to a different folder "xxxx modified" The JPEG dialogue box comes up, and I elect to save at the highest setting (12) The problem is that this saves the file at almost twice the size, yet when I compare the details, both photo’s are at a resolution of 300, and both are 2650 * 1920. I also can’t see any difference in the quality of the image.

Where do the extra bytes come from ?

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J
JasonSmith
Sep 17, 2003
the photoshop saved file is using a higher compression quality setting than what the camera saves in.
M
MervJones
Sep 17, 2003
Ok, bear with me. Why is the original almost half that of the saved copy. I could understand it if it was the other way around, with JPEG compressing the file, but making it bigger will result in more bytes (although there aren’t any more pixels)
J
JasonSmith
Sep 17, 2003
Once a file is saved using a particular setting (like what your camera uses), then saved at a higher quality wont yield any better results. It will only keep your file from getting degredated further.

That is why you see no difference in the file – the higher 12 setting does nothing to fix what has already been done to the file from the intial save.\

Try saving a duplicate of you file using a lower quality setting to see what I mean. File size doesnt have to do with total amount of pixels in a file.

What jpeg compression does is a 8px X 8px averaging of the file. Heavy compression settings will bascially destroy your file, while lesser(higher quality) settings wont be as bad.

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