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Site Graphics and Multimedia Design Forum

.png prefers screen rez?
Save as 300, reverts to 72

 5:10 am on May 2, 2003 (gmt 0)

Something I noticed preparing .png images in print resolution for shipping online.

In Photoshop (5.5) I make a new RGB, say 100 x 100 px, 300 dpi (in inches .333 x .333).

With a few lines it ends up at 30k.

Save as a .png

Open the .png again in Photoshop, check image size...

100 x 100 px, 72 dpi.

Still 30k mind you, and the new size is relative to the 'new' resolution - 1.389 x 1.389 inches - so I can change it back to 300 dpi without loss, but the resolution reported has changed.

Any idea why?




 12:20 pm on May 2, 2003 (gmt 0)

Are you using the save for web option or is it just a normal save as?


 4:11 pm on May 2, 2003 (gmt 0)

Save As.

I had at first used the Save for the Web feature then realized it probably reduces the resolution as part of its optimization scheme, so then 'Saved as' with subsequent images. These come back as 72 dpi as described in message 1.


 7:03 pm on May 2, 2003 (gmt 0)

Should use Paint Shop Pro's Export as PNG feature. Shows preview of png, and always keeps the res right.


 10:56 pm on May 2, 2003 (gmt 0)

I've found photoshop's PNG support to be a letdown, all in all... (At least in v. 6.5)

However, there are a number of PNG plug-ins available for it (mostly commercial last I looked), so if you're really interested in doing a lot of PNG output through photoshop, that might be the way to go.


 11:59 pm on May 3, 2003 (gmt 0)

I've dug out a copy of PSP 5 and it's reporting 300 dpi (118 ppc actually).
So it seems to be a Photoshop quirk. The images are OK and that's all I need to know.

Thanks for your help.


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