I can’t tell you how many times over the years I’ve had to explain the difference between raster versus vector art files. And I’m still doing it. How about you?
For this article, I thought I would explain it again and discuss some points that matter more than others.
A raster file is an image composed of a finite set of dots called pixels. Every pixel is square and assigned a specific color. If you imagine a multi-colored chess board as being a close-up of a raster image, it can help paint a mental picture of what I’m describing.
Unlike a vector file, a raster file is dependent on the resolution of the file. The number of pixels that fit into a square inch determines the resolution. A 72 ppi (pixels per inch) file means that the image is only composed of 72 pixels in that square inch. A 300 ppi file means there are 300.
Smaller pixels mean the image looks better on a computer monitor, phone, or even your television. What you need is to strike a balance based on your intention with the file. For example:
More pixels = better quality.
Fewer pixels = faster download speed.
For files, the pixels per inch is the resolution of the actual file. Dots per inch, or dpi, refers to the capabilities of the printer used. Dpi is the density of the inkjet dot placement. It aligns with the pixels per square inch rule too, so the higher the number, the better print quality.
For resolution, especially for production, you always want a bigger number. A low-resolution image is usually what someone “borrows” off of some website to use as the basis for their artwork. An easy way to tell if the image will have reproduction challenges is to just look at the edges. If they are “stair-stepped” or look jagged, it’s going to be tough to get that to reproduce cleanly without a lot of work to the file.
When you ask for a higher resolution file and your customer just changes the resolution from 72 to 300 and sends it back to you, that isn’t solving the problem. When that file was transformed, the software program had to guess how it should look and filled in areas with pixels to make the change. While you can always make resolution lower, bumping things up to a higher resolution usually has unwanted consequences (added artifacts, pixelation, and weird chunks of color fun). Resampling doesn’t always work.
For raster images, always try to get at least a 300 dpi file at the actual size it will be reproduced.
For these file types, the larger the physical dimensions of the file get, the more megabytes the file may be in size. A 300 dpi file at 12″ X 12″ in size could be a 37MB-plus file, and even larger if there are unflattened layers. That’s usually not something that can be emailed. I recommend either setting up an FTP portal on your website or getting a Dropbox account.
Raster image file size can be a good indicator of image quality. So when a customer shoots you a raster image that is 112K in file size, you may be in trouble.
Raster images are best for photographs, complex illustrations, banner ads, web graphics, and content for social media.
Vector images are based on math, not pixels. You learn in high school geometry that if you plot two points on a graph, you can connect them with a line. Plot four, connect all of them with a line, and you have a box shape. With that shape defined, you can make the line or the box a color.
What’s great about this type of image is that it can be enlarged or reduced in size and never lose fidelity.
For this reason, vector images are always the best choice for logos and type.
- Logos need to be vector files. This is so there aren’t any resolution challenges.
- All Pantone colors labeled. Specifying these in the logo art file means nobody has to guess or ask questions later.
- Fonts should be converted to outlines. This means that killer font you downloaded for free needs to be converted from that text file to vector paths so it reads correctly in the logo art file.
Vector files are always best when doing something with logos or text.
Read more about vector versus raster files on Atkinson's blog.
—Marshall Atkinson, InkSoft