This portrait of an Intermediate Egret has been heavily reduced in size to fit into this web page. This shows how the entire picture looks. This is NOT a 100% crop.
Imagine you had a photo 1,800 pixels wide by 1,200 pixels deep. Now imagine you show the photo in a way that perfectly fills a screen that is also 1,800 pixels wide and 1,200 pixels deep. In those circumstances you’d the screen would be displaying every pixel in the photo, and because each single image pixel is allocated to its own single screen pixel you’d be seeing the photo at 100%. When you see an image at 100% you’re seeing every bit of detail that’s possible to show in your image, assuming your eyesight is good enough to make out the individual screen pixels. Imperfections like noise and minute amounts of blur will become noticeable to anyone who peers right up close to the monitor to see those image pixels. When people do that, it’s sometimes called ‘pixel peeping’.
A 100% crop taken from the Egret photo shown above.
Now let’s say you cropped the image by, for example, chopping a big chunk off the side of it. The picture doesn’t fill up all the screen any more. But because you cropped it, it’s now become a 100% crop.
You could say that a 100% crop is a fragment of a full-sized image.
People show 100% crops because they want to show how good the image quality of a picture is when it’s at full size, but the whole image file is too big to put online or to send in an email. So instead of showing you the whole file they just show a fragment of it.
And another reason why people do it because they can! It’s so easy to do.
A full image (reduced in size heaps) and a 100% crop above right.
The same full image a 50% crop. A 50% crop is simply a fragment of the image showing how it looks after its image size has been reduced to 50%.
Some people look at their images at 100% on screen and worry when they find tiny imperfections. But that’s a tough and often misleading way to judge an image. It’s like worrying that a lawn is no good because when you examine it under a magnifying glass you find some blades of grass that look funny. The truth is, every image is going to have imperfections if you look at it closely enough, and there are much more important things to think about in photography. For example, noise is something that can be a problem in photography if it gets out of hand, but a small amount of noise is normal.
While pixel peeping has its place, as long as the image looks great when you print it, or when you zoom out and view the entire frame on your screen, then who cares about the details that are only ever visible at 100%? Things like composition and colour and subject matter are more important. Getting those things right is what really gets your stuff noticed.