If your present photos are 3008 x 2008 they are within a few pixels of having a perfect 3:2 aspect ratio. They are fine for 6x4 paper, which is 3:2 aspect ratio.
You divide 3008 by 3 and then multiply the answer by 2, to get the other length in pixels.
I believe the *ist DS normally shoots the 3:2 ratio which is the ratio of 35mm film.
Most non-DSLR cameras use an aspect ratio of 4:3, which does not fit on 6x4 paper without cropping.
So called, standard photo papers are all based on old camera aspect ratios.
Some date back to the early 1900s.
8x10 and 5x7 came about from press cameras that were used in the early 1900s.
The most modern size of paper is 4x6 which is based on the size of 35mm film.
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In a perfect world you would set your camera to a size based on what you are going to do with the photo.
i.e. - for printing on 6x4 paper you would select a camera setting of 1800x1200 if your printer was going to print the photo at 300 dots per inch.
But that is not practical, and downsampling a photo to a smaller size (with software) is deemed acceptable. And with the methods used by modern inkjet printers you will not see any degradation of the image.
Now if you have to upsample a photo (make it bigger), then you will cause noticeable degradation of the image. Because the software is having to generate pixels out of mathmatical guesses.
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Resample vs resize:
A difficult subject, so I ask you to visit a link on the subject:
http://www.scantips.com/basics2g.html
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I have just started shooting digital (*ist DS) and most of the shots are done as 6 megapix jpegs and some raw. I have not taken/sent any to be professionally printed yet. My question is do I have to resize the files to 4x6 even if I haven't done any cropping or can I just leave them alone and have them printed as is (they are 3008 x 2008 pixels as-is)? Also, if I do crop do I need to make them 4x6 or just make sure they are proportional to a 4x6.
I am very confused by this topic, if I have many more pixels than needed for a given picture size (and the file is large) will that cause printing problems?
Also resample vs resize ?
These are all related issues, is there a good 'general purpose' approach for handling them?

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