Tuesday, November 4, 2008
Resize Smaller Part 2
Ok, so the question came in. Why resize smaller? There's a number of reasons, most having to do with getting rid of one kind of noise or another. In the print world, we scan at the max optical resolution of our scanners, then reduce by half in this way. The resulting image tends to be less noisy, largely due to the interpolation method's decision as to what stays and what goes.
Try it and see the results for yourselves. It's not a bad trick to have in your bag. It works on images of all sizes, just remember that the really small pics will end up even smaller.
Now, about the math:
The image here starts with a pixel dimension of 1024 x 1024. To find the number of pixels, just multiply one side by the other. 1024 x 1024 = 1,048,576.
In the Width box, enter 70.7 and change "pixels" to "percent." Make sure that Constrain Proportions is checked. Click OK and you should get the resulting dimensions, 724 x 724.
724 x 724 = 524,176.
524,176 / 1,048,576 = .499 - or (for all intents and purposes) half of the pixels that you started with.
Try it yourself. Bit depth has no part to play in this equation, it's simply looking at pixels. Remember to choose Bilinear as your interpolation method here - so as to not introduce additional sharpening.
Perform your corrections as specified in the workflow, then either interpolate up in Photoshop, or let your printer do it for you (optimal for newer printers).
Keep the questions coming. And, don't forget the new self-paced e-learning Forensic Photoshop class available from the American Institute of Forensic Education.