Can someone explain what a 50 or 100% crop is?

[bouwy]

I know what cropping is, but I cannot understand how to do a e.g 50 and or 100% crop. Are there certain parameters in a cropping program that let you the size of a crop.


Thanks for your help.


Wally

[neuroanatomist]

The "100%" refers to viewing the image at 100% size on your display. With current cameras, you'd need higher resolution displays than are currently made to view the entire image at 100%, so you can only see a portion at a time. When someone posts a "100% crop" or a "50% crop" here, they are viewing the image at 100% or 50%, then cropping by selecting a portion of that image and copy/pasting it into a new file, which they post here.


Personally, I use Photoshop for that, setting the View to Actual Pixels for 100%, then using the marquis selection tool (usually with a fixed size since the max width of an image here is 800 pixels) to copy the desired portion and paste it into a new file.


Another method would be to use any image viewer (DPP, etc.), set the view to 50% or full size, reduce the size of the window to something managable, then take a screenshot of that active window (Alt-PrtScn on Windows then paste it into some other program, or Command-Shift-4 then Space Bar on Mac, although on Mac it's easier to just set the view to 100% then useCommand-Shift-4 and drag the selection box to grab a portion of the image which is saved to the desktop).


For example, here's an original image and a 100% crop of that image:








Note that you have to actually show the full size of the cropped image, which I why I selected an 800 pixel wide portion of the original image viewed at 100%. If you display the cropped image at less than full size, like the image below, it's no longer a 100% crop. That's important not just for viewing size - notice that the noise which is evident in the full size 100% crop above (ISO 3200 on a 7D) is much less evident in the smaller image below. The noise is also less evident in the original image, which is why extreme cropping has a negative impact on a final image.





Hope that helps.


--John

[bouwy]

Thanks for the info John


Your explanation is very good. I will try your method and will let you know how I went.


Thanks again Wally

[DavidEccleston]

You don

[HDNitehawk]

Wally


You see people say 50% and 100% crop, I am not sure they are mathmaticaly trying to make those exact crops. I haven

[neuroanatomist]

But I am not sure why you would want to do exactly a 50% or 100% crop.

The main (perhaps only) reasons would be to compare performance of different cameras/lenses or illustrate some technical point about an image. If someone actually needed to use a 100% crop as a final image, it would be time to get a longer lens...

[DavidEccleston]

The reason for the exact 100% crop size is to compare lenses, or show camera noise levels. That sort of thing. It can show lens sharpness, contrast, amount of chromatic aberations on high contrast edges. For comparisons, it