Creating high-quality photo prints using an ink jet printer is no trivial matter. Depending on the tonal range and color depth desired and the expected viewing platform, how you approach printing may differ. The choices you make when printing also affect how effectively you are using your printers capabilities, resolution, and ink.
So, how does one generate high quality photo prints using professional ink jet printers, such as Epson Stylus Pro or Canon PIXMA Pro, while maximizing the use of ink and the printers capabilities?
Answer
Making effective use of professional photographic ink jet printers is tricky business, especially when the statistics that are commonly used to describe these printers are vague and misleading. Learning how a ink jet printers function, how to properly interpret their capabilities, and make the most effective use of those capabilities, is possible. For those of you not quite as interested in the technical details, who are just looking for a simple answer, here you go.
Terminology
The basic terms involved in ink jet printing are as follows:
- Pixel: Smallest unit of an image.
- Dot: Smallest element of a print generated by a printer.
- DPI: Dots per Inch
- PPI: Pixels per Inch
The terms DPI and PPI, while often used interchangeably, are not interchangeable in the context of ink jet printing. A dot is the smallest element that an ink jet printer uses to create an image, and multiple dots are required to create a single pixel of an image. As such, the DPI will generally be higher than the actual resolution the printer prints images at. Most professional ink jet printers use a resolution of 720ppi (Epson) or 600ppi (Canon).
The Human Eye
The human eye is a truly amazing device, capable of seeing an astonishing range of color and tone. It does have its limitations, however, unlike a digital camera, which may have many times the resolving power of a human eye. The eye, assuming 20/20 vision (corrected or otherwise) is capable of resolving, or "seeing distinctly", details down to at most 500ppi when viewed within a couple inches. Photographs are rarely viewed at such close distances, and are more naturally viewed at around 10"-18" (25-46cm) for small hand-held prints up to several feet for larger prints hung on a wall. At these sizes and viewing distances, the human eye is capable of resolving details from between 350ppi at 10" down to 150ppi at several feet.
Print Resolution
Due to the limited maximum resolving power of the human eye, extremely high printing resolutions are unnecessary in most viewing conditions. Common handheld prints of 4x6 which are usually viewed at 10" are best printed at a resolution of 300-360ppi. Larger prints such as an 8x10, likely viewed either laid on a table or framed and displayed, are often viewed at a range of one to two feet. A resolution of 200ppi is about as much as the eye can resolve at these distances. Even larger prints, unless they are intended to be viewed at close distances, are usually framed and hung to be viewed at distances of several feet. Such large prints may be printed at the minimum resolutions of 150-180ppi, without any loss in detail that the eye can see.
Despite the frequency at which resolution is touted as the most important factor in a print, there are other factors that matter just as much, if not more. A limited number of dots may be printed per pixel, and the higher the resolution printed at, the fewer dots per pixel. At maximum resolution for Epson or Canon printers, you get around 8 dots per pixel, which gets you a total of 65 distinct tones if we have about 8 ink colors. At half the maximum resolution, you get about 32 dots per pixel, which gets you a total of about 257 distinct tones if we have about 8 ink colors. Using an even lower resolution, say 240-288ppi, you get 128 dots per pixel for a total of 1025 tones.
Ink jet printers these days include a variety of tonal range enhancing features. One of these is the ability to print with varying ink droplet sizes. Epson and Canon offer three different droplet sizes. While the variation in droplet size does not specifically increase your tonal range, it allows the printer to produce smoother tonal gradients, which ultimately has the same effect: better prints.
Printing a quality print is about more than simply printing at the highest resolution. A variety of factors, including viewing distance and required tonal range, should be taken into account. Below is a chart that indicates the available printing resolutions, the corresponding pixel size in dots, the best viewing distance, and the approximage tonal range:
| dpi | view | tones/
dpp | 1200 | 1440 | 2400 | dist | pixel
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
4x2 | 600 | 720 | 600 | 8" / 20cm | @200
6x3 | 400 | 480 | 400 | 9" / 23cm | @450
8x4 | 300 | 360 | 300 | 11" / 28cm | @780
10x5 | 240 | 288 | 240 | 15" / 39cm | @1200
12x6 | 200 | 240 | 200 | 18"-24" / 46-61cm | @1800
16x8 | 150 | 180 | 150 | 2'-5' / 61-152cm | @3000
Despite the theoretically higher number of tones per pixel at lower resolutions such as 150-200, the greater viewing distance effectively mitigates the gains. The optimal printing resolution to get the most out of your printer is likely to fall within the range of 240-360ppi.
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