Originally Posted by adrean8j
Quick novice question for you guys:
How do you calculate your "crop" factor on your shots? I mean literally (not the Crop body, as in 1.6, 1.3. I already know what that is). I mean by 100% crop, 98% crop, etc, etc....I have heard a couple different explanations and want a definitive answer....
It's been answered, but one or two of the answers were confusing. When you're editing with PS, LR, DxO, Elements or whatever, select a 50% view and the viewer will zoom in on the image. The size of the image on your screen will be determined by the resolution of your screen in pixels. So, if the image is 5000x3000 pixels and the longest full screen view of your screen is 1000 pixels, then you can only see the whole image in a 20% view. If you look at the image in a 100% view, then you'll only see 20% of its pixels on its longest edge. You'll have to scroll 5-screens to see the whole image. If your image size is 1000x800, then it would fill the longest side of a screen with resolution of 1000-pixels.
Anyway, the 25%, 50%, 100%, etc. is telling you pixel-to-pixel ratio of the actual image to the screen. At 100% a pixel in the file takes up one pixel on the screen. You're showing the image actual size.
I personally calculate my degree of crop by looking at the file size before and after crop. If it's 5000x3000 before crop and ends up 2500x1500 after crop, then I'll say that's a 50% crop. However, using that logic a 98% crop would only be 100x60 pixels, which is not what most people mean. When you say 100% crop and the screen ratio is the same as in my example above, the image size will end up 1000x600, which I might describe as an 80% crop, when others are taking into account their screen resolution and calling it a 100% crop.