Strange issue with resolution…

SF
Posted By
stanley_flomin
Jun 30, 2008
Views
292
Replies
4
Status
Closed
For some reason whenever i open up an image it seems to default that image to 240 resolution. I can’t figure out why! Even if i output an image with 72 res, and reopen it, it’ll go back to 240! Any ideas on what the heck could be going on guys?

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S
Silkrooster
Jul 1, 2008
When you change the ppi of the image are you saving the file afterwards? What do you mean by output? printing or saving? What steps are you taking to change the ppi?
SF
stanley_flomin
Jul 1, 2008
I go to image>image size turn off resample image, change the resolution, save as for web, save. Close the image and reopen it and bam the resolution is changed to 240 even if I saved it as 72. I should note that my jpegs are opened through camera raw automatically, could this be the reason?

-edit- as a matter of fact that was the cause, I just made it open jpegs normally rather then via camera raw and the resolution remained unchanged. I wonder why camera raw does this, and if its possible to change that. 240 is a strange resolution, I know 72 for web and 300+ for printing but what could 240 be for…
P
Phosphor
Jul 1, 2008
The 240ppi resolution comes from the metadata that your camera attaches to the image. Except for printing purposes, the ppi measurement means absolutely nothing.

Yes, you read that correctly: Unless & until you are going to print, you can COMPLETELY ignore any value you see for ppi.

The following link to a book excerpt (first one I found on a quick search) from books.google.com might shed some light for you about WHY 240 ppi has been chosen as the default value for resolution metadata that carries along with the image output (historically, it seems to have something to do with Epson printers native 360 or 720 D.p.i. printer dot resolution)… <http://xrl.us/i3dvu> (Link to books.google.com) The relevant info is in the 3rd paragraph on page 42.

Unfortunately, a couple things surrounding that info in the book, in part……are misleading advice. A ppi value has NO bearing whatsoever on an image file’s byte-weight.

The best primer for understanding resolution for images in the digital realm—from scanner or camera, to working in Photoshop, to scaling and using images online or for video—and when and how it matters, please bookmark, then study as you have time at the following website. It’s helped many thousands of people grasp the core concepts, myself included.
<http://www.scantips.com> Scroll down to the *Start link and begin studying there.

If you only learn one thing, it should be this:"Scan (or photograph) for output.

The only numbers for image dimensions that matter are absolute pixel values for width & height, e.g.: 4000pxW × 3000pxH. A value for ppi (or pp/cm) only comes into play when you want to decide how detailed a printed image needs to be at a specific size as measured in inches (or centimeters.)"And deciding what resolution value to use when printing via various hardware is another issue all its own.
MD
Michael_D_Sullivan
Jul 3, 2008
Except for printing purposes, the ppi measurement means absolutely nothing.

Not quite. If you are going to put text onto the image, the ppi is very important, because it determines how many pixels equal a point (which is 1/72"). If your image is 4000×3000 px, and you set the resolution to 72 ppi, 18-24 point type will be microscopic, while if you set the resolution to 300 ppi, 18-24 point type will be a reasonable starting size for putting your name and copyright at the bottom.

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