Pixels are the individual picture elements in digital images and prints. When pixels are large, the image looks mosaic. This is referred to as pixelation. But when the individual elements are very small, they become invisible to the naked eye.
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| Pixels large enough to se | Pixels invisible to the eye |
Even when pixelation is invisible to the naked eye, it can still often be seen under the microscope in dye sublimation and digitally-exposed chromogenic photographs. This microscopic pixelation in prints can occur for two reasons. Again, it could still be that the image file being printed is of very low resolution, so that the pixelation is an artifact of the image and not the print. However, most commonly today it is due to the resolution of the printing system and its own technical limitations.
In dye sublimation printing, a linear array of heating elements produces the individual picture elements along the short axis of the print, while those along the long axis (that of the paper’s travel through the printer) are created during each individual step of the paper moving through the printer. Larger heater elements are more likely to create prints with a pixelated look as are longer steps through the printer. In addition, because the dye is diffused into the paper there can be some colorant spread resulting in higher color density between the heater elements. This can create slightly dark lines down the length of the print.
In digitally-exposed chromogenic photos, the same pixelated effect can occur, though in this case it is due to the number of laser or LED exposure points across the paper coupled with the length of steps for the print paper moving through the printer. Like dye sublimation, these digitally-exposed photographs also occasionally show lines along the length of the print. Below are examples of a dye sublimation print and a chromogenic photograph magnified to highlight the pixelation.
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| Pixelated dye sublimation image | Pixelated chromogenic image |
Below are prints that only show lines along the length of the printer. The image on the left shows a magnified dye sublimation print and the image on the right a chromogenic print.
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| Dye sublimation print with horizontal printer lines | Chromogenic print with horizontal printer lines |