File Formats and Best Practices
In my travels as a comic book publisher, now t-shirt printer, I find myself answering the same questions over and over again. One of THE most common questions I get are in regards to file formats, specifically what files are best to print from. One of the most common frustrations expressed by artists and clients whom we published comics for is that he color they saw on their screen does not match what they see on paper (or on fabric for shirt printing). So here is a little primer on color, screens and file formats for all to use.
Starting with color, when you are doing offset printing (for books or comics) or Direct-To-Garment (DTG) printing for shirts you are working in what is known as four color process printing. When you are doing your work on screen you are working in the RGB color space. There is a huge difference.
RGB - The main purpose of the RGB color model is for the sensing, representation, and display of images in electronic systems, such as televisions and computers. The RGB color model has a solid theory behind it, based in human perception of colors.
RGB is a device-dependent color model: different devices detect or reproduce a given RGB value differently, since the color elements (such as phosphors or dyes) and their response to the individual R, G, and B levels vary from manufacturer to manufacturer, or even in the same device over time. Thus an RGB value does not define the same color across devices without some kind of color management.
This is why if you have ever gone to a Best Buy or other place that sells lots of televisions that all of the TV’s lined up next to each other look slightly (or dramatically) different. The TV’s are taking the incoming RGB (which stands for Red, Green, Blue) data and interpreting it in whatever fashion the manufacturer’s software is telling it to in the best way that the screen can.
Typical RGB input devices are color TV and video cameras, image scanners, and digital cameras. Color printers, on the other hand, are not RGB devices, but subtractive color devices (typically CMYK color model).
CMYK - is a subtractive color model, used in color printing, and is also used to describe the printing process itself. CMYK refers to the four inks used in color printing: cyan, magenta, yellow, and key (black). Though it varies by print house, press operator, press manufacturer, and press run, ink is typically applied in the order of the abbreviation.
CMYK stands for Cyan Yellow Magenta and Key (not black as is commonly thought). The "K" in CMYK stands for key because in four-color printing, cyan, magenta, and yellow printing plates are carefully keyed, or aligned, with the key of the black Key Plate. The weakness of blacks that are made up solely of combining the three colors led to printers to start using black ink in the key plate to go over the colors. In order to get a nice, deep black though your black must be what is referred to as a rich black, so black backed up with other colors.
The CMYK model works by partially or entirely masking colors on a lighter, usually white, background. The ink reduces the light that would otherwise be reflected. Such a model is called subtractive because inks "subtract" brightness from white.
So, when you are working on your computer and you are looking at your screen and see a color you are not always going to be able to reproduce that color when you go to print it. Some photo printers do a better job than others and, as in our place, we have a couple of printers that have more than four cartridges (our 24 inch plotter has 12 colors). These color sets were made to better reproduce full color photographs using inkjet technology, but even allowing for that the colors you see on your screen will look dramatically different if you do not calibrate your monitor to the printer and paper you are using.
“But Photoshop has all these cool effects that only work in RGB? What do I do?” The answer to this is simple. Go ahead and work in RGB so you can make use of all of the cool effects, but make sure the colors you use stay within the CMYK gamut. When you are in Photoshop for instance and using the color picker you will sometimes see a warning sign come up when you select a color. This warning is an out of gamut warning, telling you that the color you are selecting is outside of the cmyk gamut and will not create a result you can reproduce using cmyk printing.
This is why you cannot get a hot pink or a neon green color to print in offset or DTG or any other CMYK process color printing. When you are offset printing if you want an outside of gamut color, or as you may have seen on some book covers, a metallic looking ink on the cover, you accomplish that by doing an additional pass of color using a pantone color you select.
So, now we come to the question of the file format itself. Lots of my customers and artists send jpegs to print from, THE JPEG FORMAT IS ONE OF THE WORST FORMATS TO PRINT FROM. A JPEG is a compressed file format that was developed to better display images on devices, or save them from devices like digital cameras. It is what is known as a LOSSY format in that it compresses files by discarding information.
When you spend hours working on an image in photoshop or illustrator and then go to save the image as .jpg file, you are degrading that file. Sure, it’s smaller, and it looks fine on screen, but if your intended use is to print the image on a high resolution printer (like a DTG printer) or in a book or comic (using offset printing) you are basically tossing aside a lot of your work.
Zoom in on an jpeg and look at the edges of your image, you will see it is fuzzy. This is what happens to an image, even a vector image, when you save in jpg or gif format. The reason for fuzzing the edges of a high-resolution image is so that it looks better on screen. Even an HD television is not capable of reproducing a high-res image on screen without anti-aliasing. This happens as well when you lay in text in photoshop and have the text as anti-aliased. You can see this pretty well in the example image above, the bird on the left is he original photo, the one next to it has been saved as a jpeg. Yes, I know, it is perhaps a dramatic example and not every image will be this badly compressed, a lot will depend on your settings. Rest assured though, selecting jpeg as your final file format WILL result in degradation of quality. One more thing to consider, every time you save a jpeg, it re-compresses the file, creating MORE degradation. So if you send an image to a printer, and they need to do something to it (crop it or something else) and they resave as a jpeg, the image will get stepped on even further.
What file formats for printing then? Both TIFF and PNG files are what are known as lossless file formats and are better for printing. Both also support transparencies making them perfect for t-shirt files where the color of the shirt needs to show through in bits of the design. Both also print well in a CMYK environment for things like comics, books and magazines (although, for high quality print I prefer Tiff, but you can do very well with PNG).
Also, be sure you are NOT anti-aliasing your text. That was always a very common issue when artists started lettering their comics using their computers, specifically in Photoshop where the default setting for text is to anti-alias it. I remember in one instance imagining the audible groan that must have come from one artists when our editor-in-chief told him that he was going to have to re-letter his entire comic which he had apparently already flattened.
Anti-aliasing is something you would want (again) if your intended destination is a website or TV or other image that is going to be displayed on a screen. As with the jpeg, the edges of the lettering need to be a little fuzzy for the screen because even the best quality television cannot capture the straight lines of high-quality text. If you look at the example above you would think that both styles of text look like crap, but that is just your screen at work. On paper, the non-anti-aliased text will have nice, sharp lines whereas the edges of the anti-aliased text will have lots of blurry pixels in varying colors surrounding the text.
So, in conclusion, consider where your art is going to be displayed when deciding what color space and file format you work and save in. If you are working for web or other electronic displays, then RGB and JPEG is fine. Otherwise for high quality prints stick to CMYK and either Tiff or PNG.