image size and changing resolution

A
Posted By
AnnaMiller
Nov 22, 2006
Views
460
Replies
10
Status
Closed
Hi,

I am a bit confused with changing the resolution in the image size dialogue box. If I have an image that is currently at 72 ppi and I want to change the resolution to 300 ppi, do I uncheck or check "resample image"? I have been told that by unchecking resample image, the pixel dimensions don’t change and this is the "proper" way of changing resolution.

However when I uncheck resample width, and specify 300 ppi, the height of the image decreases. So when I place the image in Illustrator it is a lot smaller than the original size, if I want to scale it. would that effect the resolution?

Previously I have been chaning the resolution from 72 ppi to 300 but checking "resample image" so the pixel dimensions change.

I just wanted some clarification on which one is the proper method to use when I will ultimately go and print my Illustrator file.

Thanks
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L
LenHewitt
Nov 22, 2006
Anna,

Yes, scaling in Illustrator WILL affect the resolution.

You are wanting to increase the numebr of pixels, so you must do that with resampling on. Howver, resampling up from 72ppi to 300 ppi is going to degrade the quality noticeably, because Photoshop has to ‘invent’ the new pixels. It does this by making a guess at what the pixel should be based on those around it, but resamoling from 72 to 300 ppi means you end up with 4 times as many invented pixels as original pixels.
DM
drew_macfarlane
Nov 24, 2006
what is 72ppi used for?
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alan123
Nov 24, 2006
its only used for screen based graphics
DM
Don_McCahill
Nov 24, 2006
resampling from 72 to 300 ppi means you end up with 4 times as many invented pixels as original pixels.

Or 16 times as many, if you are using a two dimensional image, rather than a 1 dimensional one.

🙂
P
Phosphor
Nov 24, 2006
!

🙂
L
LenHewitt
Nov 24, 2006
Don, this true – I see your turkey didn’t harm your brain <g>
DM
Don_McCahill
Nov 24, 2006
No Len, I am in Canada. We did the turkey thing in early October.
IA
Ivan_Allen
Dec 15, 2006
I want to send a photo to a magazine and they insist it must be 300dpi. I have tried to change from 72 dpi without success, I can however change the size to 1280 x 960, or 1024 x 768. Is this anything like 300 dpi?
Y
YrbkMgr
Dec 15, 2006
Image|Image Size… set resolution to 300 ppi, do not re-sample.
P
PeterK.
Dec 15, 2006
If it’s for a magazine, they are insisting 300 ppi because you need that high a resolution to get a good quality image in print. Simply taking your 72 ppi image and changing the resolution up to 300 by resampling will give them the numbers they ask for, but your image will be just as poor a quality as the 72 ppi version. Of course this all depends on the actual size of the image as well. A 72 ppi image that is 10 inches across can be changed to a 300 ppi image at 2.4 inches across. The number of pixels in the image is the same, so in this example, if the photo was being used at a size of 2.4 inches or less, you would have enough pixels in that 72 ppi 10 inch image for a quality print. In this case you could simply go to image size and with resample unchecked, change the resolution to 300 and the result would be satisfactory for print.
Basically, try changing the resolution to 300 ppi with resample unchecked, and the image size that is shown is the maximum size your photo could be printed to get a good result in the magazine. If the resulting size is too small, your image is does not have enough pixels in it for high-quality printing. Taking a low-res photo off the web and trying to use it in print is a big no-no.

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