Some vendors use four inks in their low-end photo printer models. All of them use at least six inks in their high-end photo printer models. Canon, Hewlett-Packard, and Epson offer top-of-the-range models with eight inks.

In an interview with Lyra Research, of which the results were printed in an article in Publish in the Netherlands, Senior Analyst Jim Forrest told the interviewer eight inks are better because they improve the gamut and the detail in the shadows. Forrest is convinced higher numbers of inks were useless as the potentially available number of colours with eight inks already surmounts the number of tints and colours humans can discern. However, using lower numbers of colours results in a far smaller gamut, with the printer not being capable of printing all the possible colours that are present in even the most modest digital camera file.

SpencerLab publishes a report on its web site which compares HP eight-colour ink systems with conventional processing and competing six-colour inkjet systems. The report concludes that photographs printed with the HP eight-colour Photosmart inkjet system consistently outperforms both the conventional processed prints and the six-ink competing printer systems.

The Spencerlab report dates from July 2003 and is based on the rankings of 367 participants who included photography enthusiasts (defined as hobbyists and semi-professionals) and occasional photographers. They were asked to express their preference regarding the image quality of digital prints produced by a HP Photosmart 7960 as compared to digital prints produced by conventional processing and by then current competitive six-colour photo inkjet printers.
The participants were also asked to express their preference in the areas of Richness, Realism, Sharpness, Exposure, and Smoothness.

Photo enthusiasts and occasional photographers preferred the photographs printed with the HP Photosmart 7960 in every area of the analysis. They found the quality to be superior, with Richness, Sharpness, and Smoothness the most positive influencing factors. For colour-intensive images, the HP system drove preferences higher in the areas of Richness and Realism.

Today, other vendors are offering eight-ink systems as well. Canon and Epson both use the addition of primary colours, while HP keeps using grey scale colours. The Canon and Epson approach increase colour gamut, according to David Spencer, but do not add much to the gradation and transition of one colour or tint to another.

The addition of grey tints also decreases hue shifts, which in turn decreases the risk of metamerism. Dark blue therefore will be discernible from black until it reaches a level of darkness that comes close to the natural level at which people begin to confuse colours with each other (metamerism—see note on page 2).
According to Spencer, eight inks are better than six, but not all additions to a six ink system are equally good in achieving photo prints that closely match the best quality silver halide output. Furthermore, Spencer says there are yet other factors that will drive quality. The accuracy of the colour tables inside the printer’s firmware are among these, as are some other ingredients that enhance the placement of the ink on the paper.

HP PhotoREt Pro

In the interview with Jim Forrest, he said that resolution plays a role, but not as important a role as many people would expect. Ink variation and dot variation are much more important according to this analyst. David Spencer said that we are reaching the point at which photographic print quality can fully meet consumer expectations.

According to Spencer, silver halide prints, although printed at 300 dots per inch (dpi), may still look good because each dot can contain full colour. Inkjet printers create dots of much more limited colour—typically just the single colour of the ink. One vendor, Hewlett-Packard, has found a solution to this problem.

The challenge is to make the dots small enough so that they are not seen as graininess, especially in the light pastels where the traditional approach is to print a smaller number of dots. It is also important that when one colour is placed on another or alongside it, the perceived colour should not change. This is the reason why additional inks, such as light cyan and magenta and greys are desirable, more than the red, green, yellow or blue which can only increase gamut.

May 2006: Read about HP’s new flagship printer for photographers and graphic designers, the Photosmart Pro B9180.