Part 2 of the multi-part article on printing costs and quality achievable with photo printers covers the myth that single-ink cartridges would be less expensive than multi-ink cartridges. It also discusses the difference in quality between dye-based and pigment-based inks. A next part will cover the quality issues with regards to the number of inks being used.

Some vendors’ marketing efforts focus on ink spillage as a result of using multi-ink cartridges. These vendors use single-ink cartridges themselves, often in semi-transparent housing so the consumer can see the cartridge to be empty when the printer tells him so. The reasoning behind favouring single-ink cartridges is logical from a layman’s point of view.

This reasoning has it that single-ink cartridges must be less expensive as they allow the consumer to replace cartridges on a per-colour basis. Marketing hype will make consumers believe that some colours will be depleted faster than others.

SpencerLab Digital Color Laboratory in New York performed research in this area, and found the reasoning to be nothing more than a marketing stunt.

David Spencer, CEO of SpencerLab said that: “Since cartridge cost and yield are critical to determine the true cost-per-print, and most photographs do not contain one predominant ink colour (blue skies are cyan and magenta, green foliage is cyan and yellow, skin tones are yellow and magenta, etc.), single ink cartridges alone do not assure cheaper print costs. Our SpencerLab Digital Color Laboratory has tested multi-ink cartridge printers that exhibit lower cost-per-print than single-ink cartridge printers and vice-versa. The best measure is a standard, representative yield test coupled with cartridge cost to calculate cost-per-print.”

Spencer is co-chairing a committee chartered with developing such a standard for the ISO.

The ideal: A Determined Cost-per-Print

Spencer’s view of the cost equation with regards to photo printers is that vendors like HP, who are offering a combined ink-and-media package that guarantees a certain number of prints at a determined cost-per-print are closest to providing a best price/quality ratio.
HP sells Photo Packs aimed at the Home user and at more Professional users. The Home user Packs contain HP’s Premium Plus 10 x 15 paper, the latest technology 3-ink cartridge, and a Tips & Tricks Guide to get people started fast. The semi Professional Pack additionally contains the photo-ink cartridge.

The user gets the advantage of a guaranteed price per print of 0.35 €.

Quality Issues

When discussing inkjet technology, we cannot but focus on ink quality and the issue of pigment-based inks versus dye-based inks. The topic at hand—photo printers—requires a thorough discussion of the usefulness of having a 4-ink system versus a 6-ink or 8-ink system.

We will further discuss what it takes to output brilliant colours with good contrast in light areas, and accurate shadow detail. Smoothness in transitions, half toning techniques, image grain, and algorithms to change the form, position and layering of ink drops accurately will also be discussed.
Finally, we will cover Black & White photo printing requirements. 

Ink quality

The ink used in inkjet photo printers is of crucial importance to the results. This seems logical, and so it is. However, there is more to ink than meets the eye, and while all three vendors use excellent quality inks in their systems, they cannot all achieve the most natural-looking results. In fact, only one of them comes closest to a high-quality silver halide print when it comes to natural looking photographs. The reason is the choice of ink colours.

Pigments versus Dyes

Pigment inks are based on pigments which are microscopically small grains of colour. Pigments have a high colouring value, but cannot be entirely dissolved in water or any other liquid. In other words, in the best case scenario, pigments will float freely in their liquid environment and will attach to the printing surface due to the addition of glue-like substances.

Pigments have some advantages like longevity (typically an 80 to 100 years time span) and a decreased susceptibility to humidity damage. A pigment-ink print can be touched with the fingers within seconds after it has been printed.

Pigments have disadvantages as well. Because of their graininess, colour prints will lack sharpness and brilliance. Pigment-based photo prints always somewhat look like silver halide prints on matt paper. Pigment-based inks are used throughout the Epson range of inkjet printers. Some other vendors like Agfa also use Epson’s pigment inks for their inkjet products, but these products fall outside the range of what we are discussing in this paper; they are large-format (A2 and bigger) proofing inkjets where colour accuracy and workflow are more important than sharpness, glossy characteristics or even longevity (a typical contract proof will be used for a few weeks, and will last for a few months, although here as well, vendors’ different offerings vary).

Dye inks are liquid and can be easily dissolved in water. They therefore have a much less visible grain, resulting in sharp, vivid and bright colour prints. Dye inks are ideal for glossy prints. The disadvantages of dye inks are their vulnerability to humidity. The user must wait a few minutes before he/she can touch the print surface without smearing. Another disadvantage of dye inks is a reduced life span, but this has been improved and for example the latest HP ink types match or even better the life span of pigment ink prints (between 80 and 115 years, according to Wilhelm Research). Dye inks can be found in HP and Canon photo printers.

It will be obvious from the above that dye inks are better suited for photo printing than pigment inks. Dye ink based photo prints will come closer to a silver halide print’s quality than a pigment ink photo simply because of the physical characteristics of the colorant itself.
However, other factors play a role in determining the quality of an inkjet photo print.

Next issue: The number of inks used