Image by clunky_wedding. Via Flickr.
When you're talking about any sort of image, it is generally good to think of it as having a purpose--your final intention of the image. Are you editing pictures of your wedding to print yourself? Are you making graphics for your website? Are you creating art for a shirt graphic? While we know Photoshop files are made of pixels, something often overlooked by Photoshop beginners is how many pixels the image has. One thing that will help you get a better final product is understanding a property of image files called Resolution, and tailoring it to your image's purpose.
Resolution is something I often have trouble explaining to clients. Just because an image looks about five or six inches on your screen doesn't mean it's going to look good when you fill an 8.5 x 11 inch piece of photo paper with it. The reason is likely because your file is low resolution.
It can help to think of old videogames when you think of resolution. Remember how blocky Mario used to be? That's because the NES was so limited in resolution that you could easily see the pixels. The NES had Low Resolution while newer video games are High Resolution, or High Definition, to use the television term. Pixels on televisions are no different than pixels on monitors, and not that different than dots printed on a page or T-Shirt.
This image is 72 DPI, and suitable for use on the web.
Image by Muhammmad Mahdi Karim. Via Wikipedia.
Resolution is best defined as Pixel Density. Basically, pixels (dots) can be any size we want them to be. If we make them smaller and put more of them in the same space, we get a smoother looking image. The way we track Pixel Density is with a unit called DPI, or Dots Per Inch. The smaller the dots, the more of them fit in a square inch, the better your image looks. It's that simple.
Low Resolution graphics are only good for your website and for looking at on the screen. Printing them out at actual size will give you visibly jagged images, or jaggies. Yes, that is a technical term. If you've ever downloaded a small image from a website and sent it to your printer, you'll see the results very clearly.
High Resolution images are suitable for various types of printing, including off your inkjet printer, on a poster, or on a T-Shirt. When you start with a good quality image, you have a better chance of getting a better result.
My clients often send me their artwork at small sizes of 72 DPI and lower. This looks okay on the screen, but when you look at the file at the size it's going to be produced at, suddenly the artwork seems very poor. See how smooth and invisible the pixels on the first moth look? The second is the same 1 inch square of picture, but zoomed in on 72 DPI. That image would be okay if it was very small, like image above. But zoom in on 72 DPI and you have a jagged mess.
Photoshop can try and "Enhance" images by stretching them up to a larger size. But your result will never look as good as one with a 300 DPI source. This is the problem with working with low resolution. When I get art intended for T-Shirts, I'm often given pieces that look like the second image, and when I ask for better artwork, clients try and trick me and give me the "enhanced" version on the right. Just remember, Photoshop can't create information, it can only change what you give it. If you put bad information in, you'll get back a product of bad information. In this case, a bad quality image with smudgy edges. In professional art circles (as well as in other forms of using data, like programming) this principal is called Garbage In, Garbage Out (GIGO).
"Enhance it!" No, Chris Cooper, that's impossible.
From The Bourne Identity, used without permission;assumed fair use.
I often get irate when I see movies show a low quality image from a webcam or security camera, and the FBI director or whatever tells the computer jockey, "Enhance it!" Remember, what you put into an image is what you get out. If you start out with a smudgy face with no detail, if you "enhance," you'll get a blurry, smudgy face with no detail. It's impossible to add without an artist going in and making up details, all of which may be wrong. Artists can create information, but Photoshop cannot. The basic thing to learn here is unless computers learn to think and act creatively, you'll have to use high quality art to get good results. And despite what movies may tell us, we actually are quite a ways away from computers acting creatively.
The final word: If you're using a digital camera, use a high Megapixel setting and you will usually not have to think about resolution. But if you're making art in Photoshop, start with a resolution high enough for your final purpose. 300 DPI is a standard for much of the graphics industry. If you work at actual size (8" x 10" art for an 8" x 10" photo print) and start at 300 DPI, you'll find you consistently get a better product. Just remember, if you start with high resolution and shrink your image, you'll lose no quality. If you start with low resolution and blow up your image, or "enhance" it, you'll have tremendous quality loss.
What's next? Learn about about File Types, or about Pixels.
All graphics for this entry created by me are available under Creative Commons Share Alike License. All Licensed graphics available through the CC and GNU licenses they fall under.