One thing every Photoshop user should know is the concept and use of DPI. The fact is that very few people know what DPI is, unless they work with professional digital editing and printing. The concept of DPI is indeed very simple and knowing all about it will help advance your Photoshop skills immensely.
To start with, DPI means Dots Per Inch, which is exactly the same as Pixels Per Inch. This already may not mean a lot to you, but think about it. How would the quality differ between 300 DPI and 72 DPI? The answer is a lot! Something that is 300 DPI is extremely sharper and of higher quality than something that is 72 DPI.
The reason why people may not understand DPI is that everything basically looks the same on the computer screen. In fact, there is no real difference. The difference becomes apparent when you print the different DPI pictures out. One will be larger and of publishing quality. The other photo will not even be worth saving.
One thing you should also know is that mega-pixels have nothing to do with quality. Mega-pixels only have to do with the size of a print. If you have a 1 mega-pixel image with a 300 DPI and a 3 mega-pixel image with a 72 DPI, the 300 DPI image will always prevail when it comes to quality.
DPI can be changed in Photoshop as well. But you should be cautious of this. Never just simply change the DPI of a photo or image. What this will do is super-size your photo, and doing this is never good. Remember that you can never increase the dimensions of a photo. All this will do is force you to lose information. Also, while it will make the image larger and of high quality, it will make the initial image blurry from being stretched out.
Well, then just how exactly can you alter DPI? Firstly, more high-priced cameras will allow you to change the DPI. Secondly, you can use Photoshop. Instead of changing the DPI of your photo, try opening up a new canvas. When the new document window pops up, change it to fit the size of your photo and also change it to 300 DPI (the default DPI is 72). Then copy and paste your image onto this new canvas. Remember to flatten the layers. This method is a lot easier.