HP Photosmart 7960 printer

Page 15.

Day 8 - ammended

What is PhotoREt Pro?

HP's PhotoREt technology is a process of layering multiple drops of ink in each dot to produce photo realistic printed output. PhotoREt Pro is exclusive to the HP 7960 inkjet printer, this combines a set of advanced printing technologies to produce photographic quality printing (see page 14). Older models use PhotoREt IV and lower. PhotoREt Pro’s features enable, eight ink printing giving 289 levels of primary colours, 4097 unique shades of grey (six ink photo printers can only deliver 17 shades, the others are composite shades) and 72.9 million colours (the number of directly printable colours that can be produced on the printer’s palette without halftoning) - Halftoning is the process of simulating colours through spatial distribution of component colours, e.g., mixing 25% cyan with 25% yellow to make light green.

PhotoREt Pro’s expanded colour range is achieved by using the No 59 grey photo inkjet print cartridge. To remind you, the No 59 grey photo cartridge contains two shades of grey ink and a specially formulated photo black ink. When used in combination with the No 58 photo cartridge and the No 57 tri-colour cartridge, the No 59 grey photo cartridge enables the 7960 to print with up to eight inks. (the black in the No 58 is not used when the 59 is present)

In addition to eight-ink printing, the colour layering technology from PhotoREt Pro layers up to 32 - 4-5 pl drops within a single dot. PhotoREt Pro controls the amount of ink applied to each print position to produce smoother gradations between tones for virtually grain free prints.

Are there really 72.9 million colours?

HP's claim of being able to print 72.9 million colours is a big claim, I didn't even know there were that many colours. I wonder if they all have a name, Blue, Navy Blue, Indigo, Violet, Aqua, Burgundy, George etc. Fotographer posted this interesting question on the forum

"Vincent,

The point is, if PhotoREt Pro is truly producing ***addressable*** colours up to 72 million shades, it should by right exceed the sRGB colour palette and most 24-bit monitors, which only allow 16.7 million colours. But the chart you have shown, though showed that eight-colour does increase the gamut, but not by millions more, as the numbers suggest (from 1.2 million - 72 million). Could you perhaps explain that here or address it in the web site?"

The Formula that HP has used is here.

Media		Layers 32 drops of ink per pixel with up to 16 of any single colour
HP No 57
HP No 58
HP No 59

4,097 levels of Grey - n=4, m=32, p=15
72,982,173 colour combinations - n=9, m=32, p=15

I believe the reference to "72 million colors" is the number of true color combinations that the Photosmart 7960 can produce from within the full CMYcmgGZ colorspace. The full CMYcmgGZ colorspace is theoretical and contains way more than 72 million colors, but from that full gamut, the Photosmart 7960 can produce 72 million of them that are truely ***addressable*** and unique. The hard part of course is trying to convert from the source colorspace (sRGB in this instance) to the target colorspace (CMYcmgGZ) - this is what HP's proprietary halftoning and colormatching do.

You can create a device with any type of colorspace. Pantone adds green and orange I believe. If that colorspace uses 8 bits per colorant (like RGB does), then its full CMYGO colorspace would contain 2^40 possible colors. That's a big number considering that the RGB colorspace only contains 2^24 colors. The key here is that all of these colorspaces are independant of each other. Just because the RGB colorspace has a limit of 16.7 million colors doesn't mean that the CMYGO colorspace is confined by that same limit. And of course the same is true for the CMYcmgGZ colorspace that the 7960 uses. I guess you just have to understand that the source image colorspace and the destination device colorspace are completely separate - and it's halftoning and colormatching that provide the 'science' to convert any given color from the source colorspace to the destination colorspace. If the number of possible colors in the destination colorspace exceeds the source (as is the case in converting RGB->CMYcmgGZ), then it's the job of halftoning and colormatching to figure out how best to use the larger palette available to the destination device. Just because the source gamut is confined doesn't necessarily mean that the destination gamut is confined as well.

Hope this makes things clear!

The result of having so many colours is that even though the human eye can't distinguish them (or your monitor), prints will have smoother transitions, better shadow and highlight detail and reduced grain (noise).

	PhotoREt Pro 8 inks
	PhotoREt IV 6 inks

Although this review is getting slightly side tracked with PhotoREt Pro, I feel it is an important addition to the HP 7960, it enables the printer to produce photographs which other six ink printers would struggle with. I haven't got a PhotoREt pro document I can share with you at this stage, but you can view a PhotoREt overview here.

© Vincent Oliver 2003 www.photo-i.co.uk
Please use the Forum to post your questions and views.
Shopping is just a click away photo-i shop