A dye-sublimation printer or dye-sub printer is a computer printer which employs a printing process that uses heat to transfer dye to a medium such as a plastic card, printing paper, poster paper, or fabric. The process is usually to lay one color at a time using a ribbon that has color panels.

Most dye-sublimation printers use CMYO colors which differs from the more recognized CMYK colors in that the black dye is eliminated in favour of a clear overcoating. This overcoating (which has numerous names depending on the manufacturer) is effectively a thin laminate which protects the print from discoloration from UV light and the air while also rendering the print water-resistant. Many consumer and professional printing machines are designed and used for producing photographic prints.

Sublimation is when a substance transitions between the solid and gas states without going through a liquid stage; the action of dry ice exposed to room temperature is a common example. In a dye-sublimation printer the printing dye is heated up until it turns into a gas, at which point it diffuses onto the printing media and solidifies.

Prior to printing, the dye is stored on a cellophane ribbon. The ribbon is made up of three colored panels (cyan, magenta, and yellow) and one clear panel which holds the lamination material for the overcoating. Each colored panel is the size of the media that is being printed on; for example, a 6" by 4" dye sub printer would have four 6" by 4" panels.

During the printing cycle, the printer rollers will move the media and one of the colored panels together under a thermal printing head, which is usually the same width as the shorter dimension of the print media. Tiny heating elements on the head change temperature rapidly, laying different amounts of dye depending on the amount of heat applied.

After the printer finishes covering the media in one color, it winds the ribbon on to the next color panel and partially ejects the media from the printer to prepare for the next cycle. The entire process is repeated four times in total: the first three lay the colors onto the media to form a complete image, while the last one lays the laminate over top. This layer protects the dye from resublimating when handled or exposed to warm conditions.

Comparison with inkjet printers
One of the main advantages that dye-sublimation printing has over inkjet printing is its ability to print a superior color gamut. The ink used by inkjet printers cannot change color, and it is also opaque. This means that inkjet printers simulate a range of colors by varying the size and/or number of colored dots against the background of the print media. Since the inks are opaque, dots cannot be laid over each other, and so dithering must be used to create the illusion of solid colors; see also Dots per inch.

Dye-sublimation printers are able to change the temperature of the thermal printing elements in the print heads to different levels, producing different shades of each of the colored panels. More importantly, due to the properties of the dye, the dye is transparent and colors are laid on top of each other, producing true solid color gradients. As an example, a dye-sublimation printer capable of heating its thermal elements to 256 different levels can produce 256 different shades of each color, for a total of 16.8 million different colors in its gamut. Coupled with the final laminate coating, prints from a dye-sublimation printer look similar to those developed from a photochemical lab.

There are several other advantages over inkjet printing. For one, the prints are dry and ready to handle as soon as they exit the printer. Since the thermal head doesn't have to sweep back and forth over the print media, there are fewer moving parts that can break down. As the dye never enters a liquid phase, the whole printing cycle is extremely clean; there are no liquid inks to clean up and no print heads to get clogged. These factors make dye-sublimation generally a more reliable technology over inkjet printing.

Dye-sublimation printers have some drawbacks compared to inkjet printers. Each of the colored panels of the ribbons, and the thermal head itself, must match the size of the media that is being printed on. This means that dye-sublimation printers cannot match the flexibility of inkjet printers in printing on a wide range of media.

The amount of wasted dye per page is also very high; up to 95% of the dye in the four panels may be wasted for a typical print. Once a panel has been used, even to just print a single thin line, the remaining dye on that panel cannot be reused for another print without leaving a blank spot where the dye was used previously.

Due to the single-roll design of most printers, four panels of colored dye must be used for every print, whether or not a panel is needed for the print. Printing in monochrome saves nothing, and the three unused color panels for that page cannot be recycled for a different single-color print. Dye-sublimation media packs, (which contain both ribbon and paper), are rated for an exact number of prints which yields a fixed cost per print. This is in opposition to Inkjet printers where inks are purchased by volume.

For environments that print confidential or secret documents, this printing machine is a potential security risk that must be handled carefully. Due to the mechanism of printing, a perfect color-separated negative image of the printed page is created on the supply roll color panels, and the "waste roll" of dye panels can be unrolled to see everything that has been printed with the printer. For such environments the waste roll should be shredded or incinerated onsite rather than simply being discarded in the trash.

Also for home users, the waste roll from a photo printer can be similarly recovered from the garbage and used to see everything that has been printed. Since the supply roll is plastic, the lifespan of a used roll can be years or decades long, permitting image recovery long after disposal.

The printing machine used for sublimation printing are those with Piezo electric print heads made by Epson. It works by means of a tiny crystal in the head that pulsates with a small electrical charge forcing droplets of ink onto the paper with virtually no heat being generated. This print head is fitted in all Epson desktop printers and many large format printers and is the only print head that will work for sublimation printing(Photo USA Corp.)The thermal heads are found in 'bubble jet' printers like HP, Canon and Lexmark work by heating up the ink which when it expands forces a droplet of ink onto the paper.

The problem with this type of print head for sublimation is that the heat affects the inks as they are forced through the head and the ink will accumulate inside eventually clogging the print head.Also, dye-sublimation papers and ribbons are sensitive to skin oils, which interfere with the dye's ability to sublimate from the ribbon to the paper.

They must also be free of dust particles, which can lead to small colored blobs appearing on the prints. Most dye-sublimation printers have filters to reduce the likelihood of this happening, and a speck of dust can only affect one print as it becomes attached to the print during the printing process. Finally, dye-sublimation printers fall short when producing neutral and toned black and white prints with higher density levels and virtually no metamerism or bronzing.

Applications
There are two types of dye sublimation inks available in the market. The most popular one is aqueous dye sublimation ink for use in both desktop and large format printers. The other one is solvent dye sublimation ink that can be used in XAAR, Spectra and Konica printhead wide format printers. Due to the fast development of digital textile printing, dye sublimation inks are becoming more and more popular in digital inkjet printing on fabrics.