I've been having a conversation about this topic with someone I know on Instagram, Kevin of Maestro Galleria. He asked me for permission to use a few of my designs in his store, which I appreciate the asking very much, and we ended up having a discussion about the process of preparing a PNG file for DTG (Direct to Garment) printing on a t-shirt using the online dropshipping/print-on-demand service, Printful. I have some experience in the matter, but it quickly became obvious to me that communicating that experience via Messenger was not ideal. This article rectifies that by laying all the information out along with images as examples.
What is the PNG Format? Why Would I Use It on a T-Shirt?
An image file in PNG format allows some areas of the image to be transparent. Here's the Wiki about it, which is way more than you need to know. When that image is printed on a t-shirt, the transparent areas will receive no ink - they will be raw t-shirt material in whatever colour the t-shirt is. This is a very common approach to t-shirt design, and I believe it signifies that effort and some work went into making the design. Even more importantly, the unprinted areas of raw shirt within the design break up the surface of the design and allow it both breathe and be more flexible; you don't have an impermeable rectangular block of ink sitting on your chest. The top image of Johnny Cash in the example illustrates what a PNG image looks like in an image editor without a background layer - the checkerboard pattern indicates that those areas are transparent and empty. The bottom image of the pair uses a solid black background.
Selecting an Image that Lends Itself to PNG Printing
Designs that take advantage of PNG's transparency work best when they are high contrast with clearly defined edges. It's also very important to take the colour of the underlying shirt into account, such that colours that are close in value to the t-shirt colour should be avoided. In other words, when designing for a black t-shirt, avoid off-blacks and other very dark colours. The reasons for this will be explained in more detail later, as it's a little bit complicated. Similarly, images with a lot of subtle gradations of colour around the perimeters of printed areas are more difficult to work with. The transition from raw t-shirt to printed area should be as clear and unambiguous as possible, with colour values as far away from the t-shirt colour as possible.
In the above example, the image on the left lends itself to transparent PNG printing on a black (or very dark) coloured t-shirt much better than the right-hand image. The subtlety of the latter makes it a lot more challenging to prepare as a transparent PNG print (not impossible, though, and I may give it a shot at the end of this article). I should probably note here that, of course, these are images created by me using Midjourney.
Here are a couple of my designs that I think demonstrate this contrast/colour-range issue very well:
The above two t-shirt designs can be found at my online stores, Lazy River Design Works and Big Shadows - check them out!
Image Size, Resolution, DPI, and Upscaling
What this boils down to is how big do you have to make your file - what pixel dimensions at what resolution - for it to have sufficient detail to print crisply and cleanly at a size suitable for a t-shirt? This is a topic that has been wrestled with a lot online as more and more people are designing websites (which require graphics, for which this is a relevant issue) and getting into printing on items such as t-shirts. Any search on the subject of "DPI vs Resolution" will turn up many articles and videos with contradictory info. We can cut through all that by recognizing that 300 DPI (dots per inch) is the print standard of acceptable quality. Print-on-demand services like Printful have built-in DPI detectors that will inform you of your design's DPI at a given print size and whether or not it passes that critical 300 DPI threshold. Graphics on your computer screen generally have a resolution of 72 (that's 72 PPI, but never mind the new abbreviation which stands for Pixels Per Inch). That's too coarse to print IF you print that image at 100%.
The way I get around all of this is to keep my image at 72 PPI but upscale it to 5 or 6 times larger, such that an image that was, eg, 2,464 x 1,856 is now 14,784 x 11,136. I took the image below and upscaled it to 14,784 x 11,136 pixels, with a resolution of 72 PPI, and which was saved with very slight compression (95) to produce a file that is 16 MB.
If I take that upscaled image and use the Printful design interface to put it on a t-shirt at maximum print size, the design's DPI is 1,232 - much higher than the 300 required. Keep in mind that the print size here is about 9"x12" or thereabouts. If I take that exact same file and place it on a poster that is 24"x36", the DPI drops to 411 - still acceptable, but much lower.
I use Topaz Gigapixel AI to do my upscaling. They have a good and robust product that lets you make a one-time purchase rather than a subscription plan. My own personal purchase was about 10 months ago, and they have developed since then. Probably my only real complaint is that it is a resource hog. And while we are talking software, I should also note that I use GIMP instead of Photoshop for image editing. GIMP is open source, free, and does almost everything that Photoshop can do.
Ok, that's enough for now. When I return with the next installment, I'll be covering how to make a PNG, how to groom that PNG for DTG printing, and also cover some details about DTG printing that are critical to this process. Stay tuned!
Comments