jpg's changing resolution while moving

JohnS

Member
An old, perhaps simple, question.
The process:
On a Win 2000 box.
Download from webmail to desktop a .jpg. Properties says X and Y pixels and 300 dpi res.
Move to a XP Pro box via eithernet or floppy.
Properties says X and Y pixels and 96 dpi.
Open in PhotoShop and image says X and Y pixels and 72 dpi.

Who's correct? Is resolution really changing?
NOTE the the XY pixels remains the same thoughout the process.

If PS says 72 dpi then I'm inclined to try to change res. to 300. Ailising looks bad, however.

Sorry for the very basic question. I think I once knew the answer, but at age 70 I've forgotten many things. Blah.
 
Re: jpg's changing resolution while moving

The information your missing is the size in inches. Here is an example:

96 inches x 96 inches at 72 dpi
72 inches x 72 inches at 96 dpi
23 inches x 23 inches at 300 dpi

All the above represent the same amount of pixel data (6,912 pixels x 6,912 pixels)


The jpeg file specification has an slot to record an intended display size (ie 23 inches), but some software does not really use this information and simply displays the image at 72 or 96 dpi. Historically Macintosh screen resolution was 72dpi and PC's were at 96, but that really depends on your display settings nowadays.

So the most likely case is that you are looking at the same image described in different ways.

If you want to see what size you can use for print production, go to the "Image Size" dialog in PhotoShop, turn off "Resample Image" and set the Resolution to 300. Now read the dimension in inches.
 

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