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Pixel Dimensions AND Resolution.


#1
Hi all, sorry if this has been asked / discussed before. Please feel free to point me towards previous discussions if it's getting old. I work in a marketing team for a small company. We often get asked for images by our customers. I was happy that I understood resolution - Eg, a 300ppi image at 6x4". I was happy that I understood pixel dimensions - Eg, a web image at 1200x1200. Recently I've become confused by more and more people asking for pixel dimensions AND resolution. For example yesterday I was asked for a 1200x1200 image at 300ppi. Am I right to be confused? Stating "at 300ppi" suggests that you can vary the resolution of a 1200x1200 image, but surely you can't - otherwise it wouldn't be 1200x1200 any more. Sorry if this is a stupid question. I was once told there is no such thing as a stupid question... :)
 

Paul Murray

Moderator
Staff member
#2
PPI is the pixels per inch when on screen, and basically tells you how big the pixels are in an image. The lower the PPI, the larger the pixels and the more pixelated the image will look when printed at scale.

You can have two images both 1200px x 1200px, but at different resolutions. On screen they will appear to be the same size in dimensions (though one will have a larger file size than the lower ppi one), since the screen can calculate how to display them, but when you print them you'll see the difference. A 72ppi image for example printed at 300dpi will either appear tiny if printed at 100%, or if scaled up would be pixelated because it has larger pixels in each square inch.

By asking for a 300ppi image they're basically asking for an image with pixels large enough to output to print without blurring.
 
#3
PPI is the pixels per inch when on screen, and basically tells you how big the pixels are in an image. The lower the PPI, the larger the pixels and the more pixelated the image will look when printed at scale.

You can have two images both 1200px x 1200px, but at different resolutions. On screen they will appear to be the same size in dimensions (though one will have a larger file size than the lower ppi one), since the screen can calculate how to display them, but when you print them you'll see the difference. A 72ppi image for example printed at 300dpi will either appear tiny if printed at 100%, or if scaled up would be pixelated because it has larger pixels in each square inch.

By asking for a 300ppi image they're basically asking for an image with pixels large enough to output to print without blurring.
Hi Paul, thanks very much for your help, and your detailed reply. I really didn't understand ppi half as well as I thought I did! When you teach yourself you can end up with these fairly big holes in the understanding of fundamental principles.