PING Mr. Chris Cox

Hello Chris,

Maybe you can shed some light on this. Wayne Fulton and I are in disagreement about JPEG image density, in another Photoshop group. He claims, it doesn’t matter at all what it is, because it does not affect what is shown on the monitor. To some degree, I agree. However, I have one application (Vue Print) where it does matter. Making the X & Y densities different, changes the aspect ratio of the image on a monitor.

My questions: Does Photoshop read both X & Y density figures? Does it display them both in image information? If it only reads one value, is it the X or Y? Will Photoshop use only one of these values when printing?

Also, do you know why X & Y density figures were included in the JPEG/JFIF standard?

Thanks!

Here’s some snippets of the conversation….

It has an X & Y DPI of 21. This can be viewed with Irfanview’s Hex Viewer. To find the values, look for the "JFIF" zero terminated string, in the very beginning of the file header.
It’s the:
5th & 6th bytes = X density
7th & 8th bytes = Y density.
These are after the "JFIF" zero terminated string.
Uni

Wayne, if you take that image and modify its resolution within Irfanview’s image properties, maybe X=21 x Y=42, then save it, then open it with Vue Print, the image aspect ratio (monitor) will change. This MAY be a glitch with Ed H.’s viewer.

Uni

Regards,
Uni