Over the course of the last four years, I have made many, many, many photo editing errors. I think when every person is first learning how to use Photoshop, they have tendency to be a little heavy handed in their editing- especially in the over-saturation department. As I've learned more about actual photography, I've relied less and less on post-processing work. When you are taking a picture, you should act as if you can't do any post editing. If you're thinking that you can always go and fix something later, you won't take take the best possible picture. But, almost all pictures can benefit from a little post processing work and I now have a few rules that I always use when I'm editing a picture.
First thing- you don't need Lightroom or ACR, but it might be something you should think about buying. You can download a free 30 day trial of both from Adobe to try it out. I know that they're expensive, but I purchased a used copy of both off of craigslist and I paid $35 for Lightroom 3 and $40 for Photoshop CS 4, which includes ACR. There are many free online alternatives, the only problem with them is that you can't edit a RAW picture with them.
I open my RAW image in either ACR or Lightroom and do most, if not all, of my editing there. I never adjust the saturation or sharpen my images because these are two sure fire ways to make your picture look photoshopped. I almost always only adjust the contrast, brightness, and black; here is a before and after edit using only those three changes.
In the second picture, the contrast and brightness are both at 10 and the black is set at 6. If you think that your picture is under saturated, increasing the contrast and black will give you a much more natural look than it would with an increased saturation. I would just like to note that if I wasn't trying to show you that saturation isn't necessary, I would I have used lower settings to edit the picture. To me, it's still a little too much.
Below this, on the left, is the same picture where I've increased the saturation to 10 instead of the contrast- the brightness is still 10 and the black is still 6 and on the right is the one from above with contrast and not saturation
Now some people might like this picture better than the previous one, but it hurts my eyes and I think it looks a little unrealistic. Yes, it's definitely more colorful, but it also looks like it's been edited and that's not what you want. The other problem with the one on the left is that it will not make a very good printed picture. What looks okay on the computer does not always look good when printed because of the ink. A computer is capable of producing many different colors that ink printers just can't produce. So the many subtle changes in color you might see on the computer picture version will turn into one big blob of color on the printed one.
Once you've finished editing the RAW picture you can either choose to save it as jpeg or PNG or open it in photoshop. I generally will only open a picture in photoshop is if it needs some touching up, ie., blemish removal. There are a few other reasons I will do further edits in there, like adjusting the exposure on only a certain portion of the picture; something you would need to do with a photoshop layer mask.
Most people will agree that the lens matters more than the camera. So what does that mean? It means the quality of your pictures will improve much more with a better lens than it will with a better camera. If you are in the market to buy your first DSLR, and you're looking at the Canon Rebels, I would recommend purchasing only the body of the camera, without the lens kit, and buying your lens separately. Why? Because the lens that comes with camera is not very good- certainly not worth the extra money that tack on for it. You would be much better off buying the 50mm f/1.8 and it will save you about $100 in the long run.
I would also recommend renting any lens that you're thinking about buying. There are many companies where you can rent a lens for just a day, or longer, at a very low cost. A new lens isn't cheap and before spending your money you should first try it out and make sure you're getting what you want. The things you'd want to check out are the weight, ie., is it too heavy for you, ease and speed of focus, distortion of subject, and overall performance. If you are purchasing a zoom lens, you'll want to make sure of the quality of it's image stabilization or vibration reduction.
I hope this has been helpful and that I've answered some of your questions. Please email me if there's anything else you'd like to know!
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