Previewing A3 quality


Link Posted 30/08/2012 - 04:27
It occurs to me that one way of verifying the sharpness of a file is to see what it would look like expanded to A3 or 4 size. Photoshop, among others, makes it possible to magnify the image by a specific percentage. So I think my question is - what magnification must be applied to an image taken by a K5 to make it the size it would be as an A3 print?

Help appreciated


Link Posted 30/08/2012 - 10:53
That would depend (a) what resolution you were printing at, (b) whether you were matching the long side of the image to the long side of the paper or matching the short side - A3 is squarer than what comes from the camera and (c) how you were scaling it - with most scaling algorithms an image doesn't become progrssively blurrier but passes through certain particularly sharp sweet-spots.

In case that's not convinced you that's it's not a good measure, plugging some numbers in to get a rough estimate gives us this: the long side of A3 is 16.5" (assuming full bleed) which, at 240 ppi is 3960 pixels. The long size of a full resultion photo from the K-5 is 4928 pixels so to fit it to an A3 print you would need to reduce the image to 3960/4928=80% of its original size.




Link Posted 30/08/2012 - 11:14
The image at 300ppi is roughly A3. Change the ppi but do not resample the image. But to get the image to roughly A3 size on screen, zoom to a 33% view. There's no substitute for a test print though! The appearance of noise and sharpness will look different on a print (better).

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