Resolution affects the accuracy of the selection. Because the image is always just a grid of pixels, the larger those grid squares are in relation to the part of the object being selected (low resolution), the more difficult it will be to make an accurate selection. To put that in more tangible terms, a 3" by 5" image whose resolution is set at 72 PPI (pixels per inch) will be a difficult one in which to make accurate selections of detailed areas. The same 3" by 5" image with a resolution of 300 PPI would yield much better results.
Resolution Versus Selection In PhotoPaint
February 24, 2011