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16th October - 2001 Maintaining print quality when re-sizing
Q. I have recently purchased a Canon g2 which I’m very happy with, however I would like to know what size of file would be best to use if I want to print out photo size prints. The g2 has the ability to produce a resolution of 2272x1704 pixels, but when I want to reduce these to 6x4 it seems the quality is being reduced as well. Am I using too high a resolution for my needs? I also have the same problems as Barry Fishman in trying to get the desired 6x4 finished print.
(Sent by M.Brown)
dp-now.com:
To get the best quality prints from the images produced by your Canon G2, or any other normal digital camera, you should choose the highest resolution and the least image file data compression setting that is practical.
Don’t forget the printer
But don’t forget the printer too. You need to ensure that its settings match the kind of paper you are printing to. Various quality settings are usually available there too.
You don’t mention how you ‘reduce’ the picture size to 6x4 (inches). If you’re using a photo editing program, like Photoshop, for example, you could be misled by a nonsensical size setting.
For example, using Corel Photo-paint, I loaded in a photo shot using an Olympus E10. Like your G2 it has a similar 4 megapixel image resolutio (just slightly smaller at 2240x1680 pixels). However, clicking on the image properties information, it assumes the images is sampled from an original at 72 dots per inch (dpi). Divide the resolution dimensions by the dpi and you get the size that Photo-paint thinks the original image size is in inches - in this case, 31.1x23.3 inches.
Don’t re-sample your image before printing
Where you may be going wrong is re-sampling or re-sizing the image to a 4 inch (height) print but leaving the dpi setting at 72. This would result in a reduction in the pixel dimensions of the file from 2240x1680 to 384x288 pixels; a reduction in actual pixels from 3,763,200 pixels to just 110,592 pixels. In other words, you will have lost 97% of the original file’s definition!
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Above, you can see the actual difference between a portion of an original 4MP image file (left) and after it has been re-sampled to fit a 4 inch print height without changing the dpi setting from 72 (right).
To re-size an image for printing, use the print preview option of your photo editing software and size the image to fit the paper size from there. This does not affect the native resolution of the print and so preserves quality.
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