|
Maximising Monochrome Ink-Jet Print Quality
Obtaining smooth tonal gradation and dot-free highlights
Printing with colour inks
Using a colour ink-jet printer equipped with the manufacturer's standard colour inks offers two alternative methods of printing in black-and-white. Using the black ink only results in a neutral-toned print but because the intermediate shades of grey are produced by varying the distance between black dots (like a newspaper print), the result can appear coarse and grainy. If the full colour inks are used the ink dots will be smaller and in the paler tones, black ink will not be used at all and the grey will be produced by (roughly) equal amounts of cyan, magenta and yellow ink. This is not a perfect system however, and very often will result in colour casts which may vary across the tonal range. Owing to the fact that the reflective properties of colour dyes vary with the type of illumination these colour casts can change when the print is moved from, say, daylight into artificial light and so it is very difficult to produce a truly neutral black and white print. The effect is exacerbated by the human eye's great sensitivity to small colour changes in neutral prints. This variation of colour with illumination is called metamerism. In addition, over time, coloured dyes can change and so a monochrome print made with colour inks may change colour as it ages.
Using monochrome ink-sets
As an alternative to the use of colour inks, a number of manufacturers have developed ink-sets which replace the cyan, magenta and yellow dyes in the printer's colour cartridge with various shades of grey. This can reduce or even eliminate the problem of colour casts in monochrome prints, but in some cases the metamerism still exists. The use of pigments rather than dyes to produce the inks may reduce metamerism, and because pigments are more stable than dyes the longevity of the print is also improved. The PermaJet MonochromePro inks we supply are pigment based, exhibit negligible metamerism and have a long expected life so we are happy to recommend them.
Another benefit of using a monochrome ink-set is that the palest tones in the image can be printed using only the lightest grey ink, the mid tones using the mid-grey ink and the darkest tones using dark grey and black ink. This results in a much smoother tonal gradation particularly noticeable in the highlights. Splitting the tones of the image so that this is realised can be achieved using ICC profiles but this is cumbersome and not easily adjustable by the user. A similar and more flexible result can be achieved with adjustment curves which are applied to the image just prior to printing. In the case of MonochromePro these curves also adjust the tone of the print offering a choice of cool, neutral or warm tones all from the same ink-set.
A comparison of printing techniques
The differences in the results obtained using the four techniques outlined above are obvious if you scan prints made with each. The four pictures below show the results obtained using a standard Epson 1160 printer at 1440dpi on Epson Matte Heavyweight paper. The first two use Epson's standard inks, the second two were made with PermaJet VT Blax inks (the forerunner to MonochromePro and basically similar), and all were scanned at 600dpi. The larger version of each picture (click on the images below to view) shows the details more clearly.
|
|
Standard Epson inks, black ink only selected in the printer driver. Notice the coarseness in the highlights and the poor tonal gradation (Click on the image for an enlarged version).
|
|
|
A greyscale image printed with standard Epson inks and the printer driver set to colour mode. The coarseness is much reduced but still noticeable (Click on the image for an enlarged version).
|
|
|
A greyscale image printed with PermaJet VT Blax, with the printer driver set to colour mode. A similar graininess to the standard colour inks but without the coloured dots and so no colour casts (Click on the image for an enlarged version).
|
|
|
A greyscale image converted to RGB with adjustment curves applied in Photoshop, and printed with PermaJet VT Blax in colour mode. Notice the considerable improvement in highlight graininess and the smooth gradation (Click on the image for an enlarged version).
|
|
|
