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Neurotic (0) Inmate
Newly admitted

Insane since: Nov 2004

posted posted 11-08-2004 10:24

When converting a 72dpi image to a 300dpi image for print, the print size goes down. Is there anyway to minimise the loss of print size and yet maintain good quality output?

Someone advised 150dpi is fine for catalogue printing, but i am not sure if it would be as sharp.


Maniac (V) Inmate

From: under the bed
Insane since: Feb 2000

posted posted 11-08-2004 18:14

Can't offer much in the way of specifics, but I would highly recommend reading this -

Basically what it comes down to is that when an image is at one ppi, and you try to increase it, there's not much that can be done to fill in the missing information.

72 ppi vs. 300 ppi is very significant difference in how much information is present. Simply changing the resolution to a higher setting isn't going to make the missing info appear.

Nervous Wreck (II) Inmate

From: Melbourne, Australia
Insane since: Dec 2001

posted posted 11-21-2004 15:56

Bear in mind that (1) the number of pixels in an image is finite and (2) resolution and image dimensions are inversely proportional i.e. as you increase one, the other must decrease, assuming the same number of pixels in the image.

If you increase resolution from 72 to 300 dpi, you are increasing resolution by a factor of over 4 times - which means the image dimensions will DECREASE by a factor of 4. If you have an image 900 px wide by 600 px high, and its resolution is set to 72 dpi, then the image will measure 900/72 = 12.5 inches wide by 600/72 = 8.3 inches high. If you increase the resolution to 300 dpi, then the dimensions will be 900/300 = 3 inches by 600/300 = 2 inches (roughly 1/4 of original size).

Photoshop is capable of 'interpolating' - adding pixels that do not exist in the original and 'guessing' their colour by sampling the colour of the surrounding pixels. On large areas of similar colour, this can be acceptable, but in areas where the colours are different for each pixel, photoshop makes a wild guess as to the colour of the pixels you have asked it to add - and the result is not likely to be particularly good - the image will just look fuzzy.

>>Is there anyway to minimise the loss of print size and yet maintain good quality output?<<

Yes, by ensuring that enough pixels are captured in the original image - either by a digital camera or scanning a photo - so that when resolution is changed to 300 dpi, the image dimensions are still acceptable for the purpose.

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