HP Photosmart 7960 printer

Page 9.

8 ink printing

Colour ink jet printers are arguably the most versatile and cost effective way for home and professional users to produce their photographs. Photographic quality on an ink jet printer has overtaken conventional wet chemistry prints. Now manufacturers are addressing other issues such as, print life, Metamerism, wider gamut colours and b/w printing. Epson came up with a solution last year in the form of the Epson Stylus 2100 and the addition of a light grey cartridge together with the infamous Grey Balancer, this produced outstanding b/w prints. I covered this in great detail on photo-i see Grey Balancer. Epson made a giant leap forward in b/w printing with its seven inks, but it still left the user with Metamerism and colour cast problems. Other ink manufacturers such as Lyson supply dedicated monochrome ink sets, these give much better b/w prints than the average “of the shelf printer” but at the expense of having to dedicate a printer solely to b/w work.

HP have addressed all of these issues with their new No. 59 grey photo cartridge (gGz). The HP 59 cartridge produces b/w prints that are cast free and Metamerism for all practical purposes has all but disappeared. This is a three ink cartridge using Light grey (g), Medium grey (G) and Photo black (z). Although only three inks it produces 4097 unique shades of grey, the average six ink photo quality printer can only produce 17 unique shades of grey – the other greys are made up from a composite of the various ink colours. This is why you can end up with an unwanted colour cast.

Things are never simply black or white

So how does the HP No. 59 cartridge work?

The No.59 cartridge should not be thought of as three inks but as one continuous ink from light grey to pure black. It’s not the individual ink that defines the colour but how the inks combine with each other on the media that defines the different shades of grey. The real secret on how HP creates a continuous tone is in the way that the cartridge switches from light grey to medium grey and then to photo black. Below is a chart which may help you to see how the ink is being used, don't worry if you can't make or tail of it, I will show you plenty of pictures later.

As the printed colour moves up a density ramp from light grey to medium grey the cartridge overlaps colours. The light grey on its own cannot continue to lay down ink to achieve a medium grey, the media itself is the limiting factor as it can only absorb a given quantity of ink. Before the light grey approaches its maximum output the medium grey ink joins in, the light grey is still being applied but in diminishing quantities.

Printing a density ramp from paper white to pure black the light grey (g) lays down its ink in increasing amounts. By the 60 level, the medium grey (G) is activated to join in for the next stage. The medium grey in combination with a decreasing amount of light grey takes the ramp to 38. At this stage the photo black (z) is activated and joins in with the medium grey ink. As the curve heads towards pure black, the medium grey offers less ink. Pure black is a combination of medium grey and photo black.

The best bit of this No.59 ink cartridge is that is also works with the colour inks. This combination increases the range of printable colours (gamut) and gives better shadow detail. Add in the PhotoRet Pro and you have over 72.9 million colours to choose from, imagine what Rembrandt could have done with that range. The final results are better graduations and less granularity in the finer transitions.

OK. that's enough of the backgrounder, does it work?

Before moving on with the review I will explain how the ink cartridges work together. The 57 (CMY) and 58 (light cm & black) must be fitted at all times. The Black in the 58 is mainly used for text printing, so if your not a good letter writer then this ink is wasted. Either the 56 or 59 must be fitted in the third slot. The 56 is only used for text printing and CAD work (does anyone use an A4 printer for this kind of work). The 59 is intended for greyscale printing (I don't know of any inkjet printer that prints in black and white). The No 59 is also used for colour printing, this gives images greater depth as you can see in the sample below.

With No 56 ink fitted	With No 59 fitted

The pictures were both printed using the same settings on the same media (hp premium plus photo paper glossy). The prints were also scanned with exactly the same settings. Notice how the print with the No 59 cartridge has picked up far more depth, the colours really jump of the page. Placing the two prints side by side the difference is very noticeable. (The slight moire effect in the sky, is due to downsampling the image)

© Vincent Oliver 2003 www.photo-i.co.uk
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