Cropping is “cutting” the photo to remove what you don’t want, and it’s often used in conjunction with straightening the photo. Here’s an example of a before and after crop (it’s the Tyne Bridge in Newcastle and the Sage music center in Gateshead):
The idea was to show the three curves of the grass bank, the bridge and the glass building. The first image is OK, but there are some distracting elements that could do with being removed, as the traffic on the bridge, the railings and stone wall on the left, and the buildings to the right of the bridge. After cropping, those elements are gone and we’ve got a much less cluttered and much more effective image that brings out the three curved shapes more clearly:
I’ve got a real problem with keeping the horizon level when I take landscape photos, and I’m not alone. Fortunately, it’s quite straightforward to straighten a photo, especially on Photoshop. Here’s one of my more disastrous efforts, a photo of a sunset on the west coast of Greenland (admittedly, it was handheld, it was below -20C and it was low light, but still – what on Earth was I doing? I did recompose and reshoot afterward to get a more usable photo):
And here it is after straightening:
You can see from the new image that straightening also inevitably involves cropping (unless you want to have an image with sides at an angle). It’s fairly obvious why, but it does mean that it may not be possible to rescue an image that needs to be straightened without losing important details.
Saturation is increasing or decreasing the color in your photos. How well it works depends on a lot of factors, but it’s possible to give your photos much more impact by (careful) use of saturation. It’s also possible – and easy – to make them look ridiculous.
Most free photo editing programs don’t tend to offer that much control, usually having only one slider to control all the color channels, so you do need to take real care when you make changes. Having said that, here’s a photo where I’ve deliberately overdone the saturation just to show you what the effect will be :
You can see that the colors have been lifted dramatically, so the houses really stand out, but you can also see that the snow has changed color and become a rather unlikely shade of blue.
Sharpening a photo means enhancing the edges within the photo. By edges, I mean the software locates the pixels that have the greatest contrast, then lightens one side and darkens the other, which gives more punch to the image and makes it look more focused. Done well, it can make a huge difference to your photos; done badly, it can make a complete mess of them. (Sharpening is actually a process called “unsharp mask”, which despite its name, actually results in sharpening. The name “unsharp mask” goes back to the days before digital photography).
A quick note here: sharpening cannot (ever) rescue a photo that is badly out of focus.
Sharpening should always be done last, after you’ve completed all your other edits. However, bear in mind that your camera may actually apply sharpening when you take your photo, so you may want to check your manual first and be careful not to overdo things.
Here’s a photo of a nice waterfall (Skogarfoss in IcelandA
You can see it looks a little out of focus, and that’s from a decent (if a little elderly) SLR camera. Here’s the same close-up with some careful sharpening applied:
You can see that it looks more in focus and, well, sharper. And here’s the same image again with too much sharpening applied:
Not nice at all. In short, careful sharpening can improve your image, over sharpening can ruin it, always sharpen last, and you can’t ever recover a badly focused image, no matter how much sharpening you do.