Multihead BO (theoretical more or less)
2003-12-29 by Ernst Dinkla
I'm interested in BO printing for esthetical reasons (Tri-X grain Rodinal 1/25> document paper prints etc in the past) but do not have the right printers in house. I've no experience other than having seen some prints with Epson dye with a 1280 and I wasn't impressed, the greyscale is alright but the consistency isn't, banding being the main problem. My 9000's here (Generations black or Ultratone black) are better in consistency + linearity (Wasatch SoftRip) but the droplets are too big. I've written it before that I think there's a way to improve BO printing by using more nozzles than the nozzles of the black head only. If the quantity of black ink per head is reduced by the number of heads used there must be a gain in consistency and quality. A driver that allows linearisation per head on top of that should improve the consistency even more. There still is a need for a printer with small droplets and that's where I miss some information. A 4 colour printer should be adequate. The new R800 (7 heads, not yet available) has the finest droplet size so far but which existing 4 colour printer comes next ? How is the droplet size distribution, 2>3 sizes per resolution setting? How many nozzles per colour ? What would be the best candidate ? A3/A4 size. Suppose one can use three heads at 1/3 of their normal ink quantity and get the smallest droplet size (of 3 sizes) for the three heads when printing 100% black. If there's one that has 4 droplet sizes take 4 heads. Next choice is the amount of nozzles per colour, the more the better. Would that give an improvement over a single head BO print with the same printer ? There's no gain in smaller droplets at the highlights. There should be a gain in smaller droplets used from 33% up to 100% if that is actually working out as nice in practice as in theory. Bleeding could spoil the fun though the ink amount is the same and it takes more time to lay down 100% from 3 heads with finer droplets than from one with bigger droplets = more drying time. The same amount of ink in smaller droplets has however more total circumference length which should increase bleed effect. That can be compensated with linearising but small changes in humidity and papercoatings could show faster in multihead BO printing than in singlehead BO printing. If linearisation is an easy task it should be done daily. 3 times the nozzle amount must add to the consistency, especially on banding, the chance that a nozzle doesn't work gets 3x higher with the number of nozzles but its effect will be reduced with 2/3 as well. The same for nozzle deflection. A total blocking of one nozzle is just one state of quality decrease and its one that is easily noticed. Much more frequent is a permanent difference between the outputs of nozzles. That is much better compensated in multihead BO printing than it is in singlehead BO printing. There should be a smoother tonal gradation with multihead BO printing from 33% to the shadows and an overall better consistency which should in itself improve the smoothness of the highlights too. There's one thing that may spoil the whole concept. Are the dithering, weaving routines in Black Only printing the same or similar to the CMYK routines ? In QTR or another driver? QTR has an advantage as not that many RIPs will drive the desktop models with their finer droplets and QTR has good routines for dithering etc. The Wasatch SoftRip that I have could do all but lacks in desktop printer drivers and its d/w routines are not that good. Taking out one of the CMY channels could address the interference of black generation in some drivers and RIPs. I still have PressReady that I used for a 3000 and wonder whether that RIP could be used by feeding it odd CMYK files. Are there pitfalls that I missed ? Ernst