The Best File Types For Printing Perfect Custom T-Shirts
October 26, 2020
One of the biggest obstacles to a successful, high-quality print comes early in the process when a customer submits a low-resolution art file. This is the number one issue that our Art Department deals with, followed by copyright issues and what to have for lunch.
In this post, I’m going to talk about the two main file types you should be aware of and their characteristics, with examples of each and brief descriptions. And I’ll go over the reasons why some are better than others, plus a short list of file types you should avoid if possible.
This is not the most exciting topic, so I’ll try to make it interesting and you try not to fall asleep. Deal?
What’s the best file type for printing?
There are two main types of image files: vectors and bitmaps (or rasters). A vector file is by far the better file type. It will always produce the best possible result, with very few exceptions. Bitmap files can be great– and necessary in some cases, particularly photographic images– but they should be high-resolution with minimal compression to get the best results. So the important point with bitmaps is that it’s not as much the file type that makes the difference, but the quality of the file.
Here’s a graphic showing the two main file types and examples of their formats:
The files that tend to be the most problematic are low-resolution and/or highly-compressed bitmap images. They will require more work to prepare them for printing and will sometimes need to be recreated entirely. I’m going to explain how to evaluate your files for quality. First, let’s define the difference between the two main file types. Still with me?
What’s the difference between a vector file and a bitmap file?
A vector graphic is defined by mathematical points, rather than a bitmap graphic, which is made up of a grid of pixels. Each of the points and the way they relate to each other define the lines and shape of graphic elements. Other data points include colors, gradients, type, and effects. The key feature of vector files, and what makes them so valuable for printing, is that they are infinitely scalable. In other words, you can resize the file as big as you like without losing any image quality– which is not true of bitmap files.
Another nice feature of vector graphics is they tend to be much smaller in file size than bitmap graphics. The reason for that is simple: bitmap files must store the data for each individual pixel, while vector files only need to store the points that define objects. For example, let’s take a look at the RushOrderTees logo.
On the left is a close-up of the bitmap version. On the right is the vector version, shown in “outline” view. The bitmap file needs to store the data for each of those pixels you see; whether they are black, white, or various shades of gray which describe the edges. The vector file, on the other hand, only needs to store the data for each of those points, how they relate to their adjacent points and the fill color. One is like memorizing a whole book word for word, the other is just memorizing the summary and the number of pages.
As you increase the size of the bitmap image, the edges of the graphic will become more and more blurry, or pixelated. On top of that, the file size itself will increase, because the number of pixel data it needs to store will grow exponentially with the size of the image. That single book to memorize can become a whole set of encyclopedias. The vector file, no matter how big you make it, will keep those clean lines you see and keep the same exact file size because the mathematical formula that stays the same– independent of image size.
A bitmap is like memorizing a whole book word for word,
while a vector is just memorizing the summary and number of pages.
Both vector and bitmap files can take many forms. Most graphics programs will allow you to save out your image as any number of file types. I’m going to give you the main ones we see on a day to day basis and tell you a little about them– just enough for you to know what you have, or what to save your file as.
Vector file types can be compound files: that is, they can contain bitmap files within them. If this sounds confusing, let me put it this way: a vector file can contain bitmap files, but not vice-versa. It’s fairly common for a vector file to have photographic elements or gradients, but the layout, shapes, and type are all in vector form.
Here are the three most common vector files used for printing (and our favorite file types to receive art):
PDF (.pdf), which stands for Portable Document Format, is one of the most popular file types, and for good reason. It was designed to be standardized, meaning it can be opened or viewed on just about any operating system, without needing the app that created it, and will retain its original fonts and layout. PDFs can also contain “rich media” such as GIFs, 3-dimensional objects and video clips. Just don’t ask to print those on a T-shirt. (We tried, it doesn’t work).
EPS (.eps), which stands for Encapsulated PostScript, is one of the standard vector file types. It’s a reliable format that tends to be self-contained, so it’s ready for action. There are lots of programs that can save out EPS files, such as Adobe Illustrator, Photoshop and InDesign, even CorelDRAW. One big program that will not allow you to save out as EPS is Microsoft Office. But that’s ok, because please don’t use Office to make designs.
AI (.ai) is Adobe Illustrator’s native file type. We love these because it’s the premier vector graphic program, so the person who made it is most likely a professional. If you’re in the market for a decent vector editor but don’t have the budget for Adobe Illustrator, there a free program called Inkscape that people seem to like. In fact, we use it just for converting CorelDRAW files (.cdr) to something we can open in Illustrator (.eps).
Bottom line: If you’re not sure which one of these you should save your file as don’t stress about it. Any of them will work. If you want to use the most versatile format, that would be a PDF.
VECTOR FILE PRO TIPS
Creating “Outlines” of Your Fonts
When you work in vector format, the fonts you use are from your own computer and do not automatically send along with the file. This can be a problem if your printer doesn’t have the same font. The default state of the text is “live” which means editable. If you need to keep your fonts “live” in the file for whatever reason, you will need to send your printer the font file along with the vector file. If you are done editing the text, you can avoid missing font problems by creating “outlines” of your type. In Illustrator, select all your type, and under the “Type” menu, select “Create Outlines”. This will convert all your fonts into text shapes and make them ready to be printed.
Placed Files vs Linked Files
When placing a bitmap file into a vector document, some people will accidentally “link” the file rather than place it. This creates a reference image that appears in the preview, but whuump whuump… is not there when you open the document. If the linked file is not included along with the main file, it’s not going to work. So be sure to uncheck the “link to” box when you’re placing a file. And that’s… one to grow on.
Bitmap Compression Settings for PDFs
If you have bitmap images placed within your vector file, PDF will try to “compress” those images (we don’t want that). So when you’re saving out, check those settings: Click on “compression” and it will ask what ppi (points per inch) you want to downsample. In the pull-down menu, choose “Do Not Downsample”. (I’ll explain compression in the next section). Or, if you need to reduce the file size, you can set it to 300 ppi, which is a high resolution for printing. So if you placed an image that is 8″ x 10″ at 300 ppi, but changed it’s size in the document to be 2″ x 5″, the resampling function will rasterize that graphic with 300 ppi at its new size. By the way, congrats if you understand this and have not fallen asleep yet.
Bitmap / Raster Files
Bitmaps, also known as raster files, are the most common category of image files out there. The vast majority of files you see on the web are bitmaps. The name alone should tell you something about it: it’s a map of bits. In other words, it’s a grid of pixels with information stored for each one of them, related to their position, their brightness, and color.
What’s the difference between bitmap and raster?
Not much. The difference is largely semantic so the terms tend to be used interchangeably. To get technical, a bitmap represents an image that has been rasterized: that is, generated by a scanning pattern of parallel lines. So if you have a vector graphic, and you want to display it on the web, you would rasterize that image to convert it to pixels. The word bitmap can be traced back to its origins as an early Microsoft image file format called BMP (short for bitmap). This format is rarely ever used since there have been so many advances since then. If you see one, it may be leftover from the ’90s.
Here are the three of the top bitmap/raster file types for printing:
JPEG (.jpg), short for Joint Photographic Experts Group, is designed to encode photographs. It’s the most popular format used on the web and has become the defacto standard image format. It’s ideal for rich colors and gradients. JPEG does use compression, so one drawback is you have some data loss every time you save it. More on compression coming up. When working with a large file in Photoshop, it’s best to save it as a PSD or a TIFF to avoid the loss. Realistically, you only need to save as a JPEG as the last step.
TIFF (.tiff) stands for Targeted Image File Format (no, it’s not short for Tiffany) and was originally designed as an interchange format between scanners and printers. It’s become wildly popular over the years among photographers and graphic designers because it’s excellent compression. Image files tend to be larger than JPEGs, but the tradeoff is worth it for retaining the quality. So if you have a TIFF and also a JPEG, now you know which one we prefer. TIFF files can support layers and vector paths (outlines, clipping masks, fonts, etc).
PSD is simply a Photoshop document. It’s Adobe’s native format for their industry-standard graphics program. It’s hard to overstate how popular this product is. I’ll just point how it’s become a verb: to “photoshop” something means to digitally alter an image. Although there are competitors in this space, Photoshop has stood head and shoulders above the rest for decades now. (If you want something similar for free, there’s a great tool available online called Photopea which does much of what Photoshop can do.)
If your file has layers, transparencies and other information, that can be very useful for a graphic designer or your printer– but it can weigh down the file size. So just Zip it for sending.
Bitmap/Raster Files with Transparent Background
Now lets a look at a couple file formats that support transparent backgrounds. This doesn’t apply to vector formats because in their files, an object is either there or not (no need to remove a background that’s not there). Objects can have partial transparency and can be stacked on top of each other infinitely because the image is not flattened into a bitmap.
Here are the two most common bitmap/raster files used for printing that support transparency.
GIF, short for Graphics Interchange Format, is one of the oldest image files, going way back to the ’80s at a company called CompuServe, which everyone forgot about. Although it’s still widely used, it’s features are rather limited compared to the other file types. It can only support 256 colors, which makes it one of the worst choices for image files to be printed. There is typically significant work to be done and limitations to the print quality. Stay away! But if you want to make an animated image for the web, the GIF would be your go-to.
PNG stands for Portable Network Graphics, and was developed to be an improved, non-patented replacement for GIF. Unlike GIFs, PNGs can support millions of colors along with an alpha channel (transparency). The other nice thing is there is no compression, so we’re not losing any important image data when we save the file. This format was designed especially for images on the internet, and at this point, it’s second only to JPEGs as far as popularity. Fun fact: According to Wikipedia, the original acronym was PING which stood for PING Is Not GIF.
Honorable mentions: Both PSD and TIFF file formats also support transparent backgrounds.
What’s so great about a transparent background?
When it comes to setting up a file for printing, having a transparent background is ideal. It gives us a head start on the separation work and leads to much better print quality. If the artwork is flat, but has nice clean edges and is made of simple solid shapes, there’s a lot less to worry about. If a flat graphic is on a white background, and we’re printing on white T-shirts, there’s typically nothing to worry about. The ones to look out for are flat images that fade into a black background, yet will be printed on white. These can create all kinds of extra work, and more importantly, could affect the quality of the print.
Let’s look at an example. Here’s an eagle named Frank over a US flag that is fading out into the background.
Above shows what it would look like on black, and below is how it would look on white. In both cases, there is no extra work involved in the separation and the print looks like it’s naturally fading into the background.
Now let’s look at what would happen if the file did not have a transparent background. Below shows what it would look like if we started out with a black background but is printing on white, and all the outer black pixels are removed. The reason the edges look so bad is that there’s no easy way to knock out the background when something in fading out this way. It can be done but involves lots of careful work with an eraser tool with soft edges. And it still won’t have the quality you see above.
Now here is the opposite: starting with a white background, and knocking out the white outer pixels to print on black. Again, the designer would need to go in with an eraser tool can carefully fade it. This can occasionally require hours of additional work, as a direct result of not having a transparent background. Frank is not happy about this, you can tell by his face.
Bottom line: whenever possible, use the file with no background.
If you’re creating a file from scratch, save as a PSD or PNG with the background set to transparent. It saves lots of work down the line and will prevent the print from having terrible looking edges. Plus it makes Frank happy.
Resolution and Compression
These two factors will determine your image quality more than any file type it’s saved as. This part gets a bit technical, but it’s important. If any of this is confusing, just send us your image files! We’ll be happy to evaluate them for you for free and let you know if they will work or we need something better.
What is resolution?
Essentially, the resolution of an image is an indication of the amount of detail it can hold, which is very important for printing. The higher the resolution, the more the detail. In more specific terms to graphics files, it’s the number of pixels, measured in pixels per inch (ppi) or dots per inch (dpi). And the more pixels, the better. The resolution of web images is typically 72 dpi, which reflects the screen resolution of most computers, but is far less than ideal for printing.
What’s the ideal resolution for printing?
Here at RushOrderTees, we ask that submitted image files be at least 200 dpi at full size. The full-size part is key; we often get files that have a higher resolution, but the actual image size is a fraction of the size it’s going to be printed. So if your graphic is for a full-size back print, your file should be at least 200 dpi at 12″w x 14″h. Pop quiz: how many pixels is that?
So does this mean that 500 dpi is even better? Yes it is, but it may be unnecessary. There are diminishing returns that occur after 300 dpi. Anything more than that can become overkill. So for ease of storage, uploading and emailing, it doesn’t need to be bigger than 300 dpi at full print size. That being said, we won’t ever kick an oversized file out of bed.
If the resolution is really low, we go back to our customers and ask them for better files, which can delay the process. To avoid this, make sure you submit the highest quality files you have. Below is a graph I made to give you an idea of your image quality– and if you should start working on getting bigger/better files.
Important: if you have a smaller file, simply scaling it up in Photoshop is not going to do the trick. While it does help a bit by smoothing out some of the rough edges, it doesn’t have the additional image data that comes with a larger sized file, which is the difference that makes the difference.
This is a factor that gets overlooked fairly often. Mostly because it’s hard for the average person to see, even if they know what to look for. But if you zoom in closely, especially using an image editor, you’ll see something called artifacts. No, not the stone tools they find on archeological digs. Image artifacts are weird-looking clumps of pixels that are leftover from compression, and they can make or break an image’s quality, so let’s talk about compression briefly to help you avoid it.
What is compression?
Simply put, compression is how we get file sizes to be smaller, making them easier to store, send, share, and post online. There are two main types of compression: lossy and lossless. As you might have guessed, lossy will reduce the quality of the image to varying degrees. Lossless will leave the quality intact while still reducing the file size. Typically, you will want to save your image files with lossless compression such as TIFF or PNG. But even lossy compression such as JPEG can do it without much effect on the image, as the data it discards is barely noticeable. But when you set your compression setting too high or resave the file over and over, things can get ugly.
Let’s look at an example. Can I get a volunteer pug from the audience? Here are three levels of JPEG compression, at 72 dpi:
As you can see, the image quality degrades as more compression is used. Here’s the part where a lot of people will say “Hey M, that doesn’t look too bad. I can still see the pug and read the type.” Here’s the thing: we’re looking at a small image on a screen. While 72 dpi at 2.5″ wide can be fine for a small image like this on the web, we will need to scale the image way up to 300 dpi at like 10″ wide for printing. Which is what, like 10 times the size? You can do the math.
So let’s look at those same exact images but zoomed in to show the actual pixels we’re working with. Pay special attention to the blocks and blemishes that appear (artifacts), and how the type degrades. I think you’ll notice the problem.
Bottom line: Don’t let your images be pugly. Use a high resolution, low compression, and transparent background.
How to convert a file to vector
So let’s say you have a low-resolution JPEG and you want to convert it into a nice clean vector file, is there a way to do that?
There are various free online vectorizers but be warned: you get what you pay for. Results may vary. Some restrictions apply. Ok, it’s mostly crap. You’re much better off purchasing a good one like Vector Magic.
If you already have Adobe Illustrator, you’re in luck: it has a built-in feature called Live Trace. It takes a bit of trial and error to get used to. Make sure to expand the advanced features and play around with different settings to achieve your desired result. And of course, there are plenty of tutorials and videos online to help you out.
You could also just leave it up to our Art Department. We do this all day every day. And there’s no charge for basic image repair. Just let your sales rep know what you’re going for, or add a note to your online order, and we’ll take care of it for you.
About the Author
A graduate of the Multimedia program at the University of the Arts in Philadelphia, Imri Merritt is an industry veteran with over 10 years of graphic design and color separations experience in the screen printing industry.