File Setup
Your file’s color space determines whether or not it will show up correctly when it is displayed. Failure to select the correct color space in Photoshop, or another program, will cause color distortion when displayed, and that looks like crap.
Resolution refers to the display quality of an image, determined by the amount of detail that can be displayed. Low resolution looks like the donut on the left. High Resolution (Hi Res) looks like the donut on the right.
Raster Vs. Vector Images
What It Is
An image made up of lots of tiny dots (pixels). It can be made smaller but cannot be made bigger without sacrificing quality.
What It’s Made Of
Pixels
More Detailed Definition
If you have a photograph from an old flip phone, it’s not going to be made from as many pixels as if it were taken on a DSLR. If you want to put that flip phone picture on a billboard, you can stretch it to that size but it’s going to be really blurry because Photoshop can’t accurately guess what to fill in the gaps with. The more pixels the picture is made of, the bigger you can make it and still have it look good.
Identified By
Photographs and complicated images. It’s important to note, however, that while photographs are always rasters, an image can look like anything and be a raster.
Common File Types
.jpg/.jpeg, .psd, .tiff, .png, .gif
What It Is
An image that can be scaled up or down to any size without loss of quality.
What It’s Made Of
Equations, generally basic lines and curves
More Detailed Definition
If you draw a circle in Illustrator, your computer stores "πr²," not a bunch of dots in a circle shape. If you make the radius 2 inches, it plugs two inches into the equation. If you make your circle the side of the moon, it plugs 1,079 miles into the equation. Either way, you’ll get a precise shape with no loss of resolution.
Identified By
Shapes (including letters) and simple imagery. Because every line and curve in a vector has to be an equation, there is only so detailed they can be. Even at their most complex, they have a kind of "paint-by-numbers" look. Vectors are perhaps their most self-actualized when used for logos.
Common File Types
.ai, .eps
Note: the terms “raster” and “vector” refer only to digital images, because the relevant question at hand is how big you can make the image. When printed on paper, an image is made of the dots of ink that were used to print it no matter what you do. In a sense that makes it a raster, but that also makes it stuck.
Also important: you can make a vector into a raster (that is, save the pixel data at a particular size) which you may need to do to use it in certain contexts. Note, however, that you can never convert a raster into a vector, no matter how simple it looks or how forcefully the client asks you. If you see a raster image you want to work as a vector, you would have to start from scratch and recreate it yourself.
File Types
PSD
The PSD is Photoshop's editable file format. Whatever you create in Photoshop will be saved in this format so you can go back and change it later when the client definitely has edits.
JPEG
A JPEG (or JPG) is the default, and most widely used, image format. It's a flat (non-editable) file that is supported basically anywhere (most notably online). It has a great quality to file size ratio. The main shortcoming is that it doesn't support transparency, so any transparent sections will be saved as white.
PNG
PNGs DO support transparency, so that's what they're best for. If you need your logo cut out and put on a picture, .png is your guy. While they can actually do everything a JPEG can do, and are supported most places, they also tend to have bigger file size, so if a JPEG will do the trick, use a JPEG.
GIF
GIFs are pretty crappy quality, but they can move.
You probably knew that, but any excuse to make a spinning donut.
AI
AI files (.ai) are Illustrator's editable file format. They're used for creating vector files, and like Photoshop have good layering capabilities for long-term editing ease.
EPS
An EPS (.eps) is the default vector file format. It can actually do a lot, but this is what it's best for. When somebody asks you for your logo as a vector, they're asking for an EPS.
INDD
InDesign files (.indd) are obviously InDesign's editable file format. They're mostly for you to create print-ready files, but sometimes the printer will want to work with the .indd directly.
A PDF is the published version of a print-ready file. While PDFs can't really be edited (they can a little, but it gets weird fast) they can be interactive, which is frequently useful. PDFs can contain all the necessary info for printing, as well as being a great computer display format. They also allow you to combine vector and raster formats.
Layers
Like layers on a cake, elements in Photoshop, Illustrator, and InDesign stack on top of each other. Every piece you add to your project will make another layer in your larger stack of components. Layer examples include pictures, blocks of color, adjustments (for example, making the components below it brighter or black + white), text, and much more. Layers act in 3 dimensions, so a layer will affect all the ones below it (for example, a black and white layer will make everything below it black and white, but not anything above it). Layers can also be grouped and/or clipped – that is, associated only with one or several other layers.
An Intro to File Dimensions
We all know what dimensions are, but because of resolution they work a little different in design. The most important measurement for files created on a computer is the number of pixels wide and tall. People will often describe file size in inches, but unless we know the number of pixels per inch that information means nothing. If a files is 5" x 7" but the PPI is only 5, then the file is only 25px by 35px - too small to do anything. However, if the file is 300 PPI, it's ready for print.
Conversely, if you change the "resolution" of a file, you haven't necessarily changed the size of the file, even though the number of inches will display differently. An 1200px x 1800px file at 300 PPI is 4"x6". If you change it to 72 PPI in Photoshop, it will now read 16.66" x 25" – but you haven't actually changed hte size of the file, just the way it's read by the software.