Sometimes, (okay, most of the time) when working in Photoshop, you have the need to select stuff. There are myriad ways to do so: multiple tools, different techniques, and also varied results. Some selections are better than others and some techniques work better in specific situations. Here we are only going to cover one quick and painless way to select all the stuff on one layer.
First of all, for this selection to work, an image needs to have a layer with a transparent background. The image below (from the Samples folder in Photoshop) has 8 layers, 7 of which have stuff on them with transparent backgrounds.
Let's say you wanted to select all the nontransparent stuff on a specific layer, the "ColorfulFish" layer for example. That's the layer with the big yellow fish on it (The layer is highlighted in the image below. You don't have to have the layer you want to do your selection on highlighted, I just did that to show which layer my cursor is going to be on.) When your mouse cursor hovers over the layer thumbnail, it turns into a hand. The big black arrow in the image below is pointing to the cursor (now a hand) hovering over the thumbnail.
When the cursor is hovering over the layer thumbnail, hold down the command key (the key with the apple on it for the Mac folks). Then a selection square appears on your cursor hand, just like in the image below.
Now with the command key held down, click the mouse. And ta-da! You have now selected everything on that layer that isn't transparent. The cursor just has to be over the layer thumbnail, it doesn't matter where on the thumbnail you command-click.
Okay the image above with the three black arrows is showing which fish were magically selected with just one click, but it's pretty hard to see at that small size. Here is a close-up. Only the three fish that were on the "ColorfulFish" layer were selected.
And that's it. Easy, right?
You know what to do from there. You can modify your selection edges, apply an adjustment to just that part of your image, or whatever you want. Just remember that for this trick to work, you have to command-click on a layer with a transparent background. It won't work on a white or solid colored background.
