OK, this one is pretty simple but it has to be done to my image, so what the heck.
My image isn't very straight. It seems that I always tilt to the right when I freehand with the wide angle. I'll have to work on that.
I'm going to grab the Measure Tool, which is hidden underneath the Eye Dropper.
To get to it, click on the eyedropper and hold the mouse button down a second to get the flyout menu. Then click on the Measure Tool. Or simply press "I" a few times - the first time will select the Eye Dropper, then the Color Sampler, then the Measure Tool.
Now that I have the Measure Tool I want to measure the angle of something that's supposed to be straight. I'm going to pick one of the trees over on the right, click in the center of the trunk at the bottom, drag up and click again in the center of the trunk at the top.
Next I choose Image... Rotate Canvas... Arbitrary. You'll see that Photoshop has automagically entered the angle of the line that I drew with the measure tool! (BTW, thanks to Chris Bailey for pointing this out - I used to do this the hard way!)
Click on OK, and:
Now we have to crop the image to get just the good stuff. I usually use the Marquee tool for cropping, but this calls for the Crop Tool. With the Crop Tool you can grab the sides and change the dimensions until you get it perfect. Note the little squares in the middle of each side - grab one of them and drag to resize the Crop window.
I will usually zoom in to make sure that I'm getting the maximum area out of the original.
When satisfied, choose Image... Crop or simply double-click inside the crop area.
Notice that I lost a bit of the image due to the tilting. The original was 600x400, but now I'm down to 591x387. A small price to pay for a straight image.











