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Author Topic: Lumejet Process Overview  (Read 5554 times)

amolitor

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Re: Lumejet Process Overview
« Reply #40 on: February 26, 2018, 11:51:28 PM »

Yeah,  I get that they're printing dots at 400dpi, but I feel like if you're going to include a paragraph on the 576 LEDs then I ought to
be able to work out what the paragraph means, you know?
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Mark D Segal

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Re: Lumejet Process Overview
« Reply #41 on: February 28, 2018, 09:31:43 AM »

Yes not a very impressive review (also a tough read) gotta wonder why it even got reviewed...to warn people off?

Doug, you ask why Lumejet got reviewed, and whether it was to "warn people off". I reviewed this one and I've done enough reviews for this site, that I feel I can share some insight that may answer your question. Reviews on LuLa are usually the result of the reviewer believing (and if it's not the publisher himself, the publisher agreeing) that the product or service is worthwhile bringing to the community's attention, normally because it is new, a novel take off on something not so new, or has noteworthy qualities. Speaking for my own work, my interest is primarily to explore the merits, call the shots as I see them and let people make up their own minds about whether they want to buy or not buy. No product scores a 100 and every reader has their own taste about how important any particular feature or issue is to them. Anyone should be hard-put to view the concluding paragraph as "warning off", including due consideration of various objective factors I discuss in the body of the article. Sorry you found it a "tough read". Others have raised several specific points deserving further elaboration. Hang-in, there's more to come. 
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Mark D Segal (formerly MarkDS)
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Re: Lumejet Process Overview
« Reply #42 on: February 28, 2018, 10:35:56 AM »

Peer review is a bitch  :(
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Andrew Rodney
Author “Color Management for Photographers"

hrwilliams

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Re: Lumejet Process Overview
« Reply #43 on: March 04, 2018, 05:35:46 PM »

I would like to introduce myself. My name is Huw Williams. I am the Chairman and lead investor for LumeJet Print Technologies, which offers the L.Type print service reviewed by Mark Segal last month. I have been a reader and great admirer of this site for a couple of years now and have learnt an enormous amount from the site itself and the forum, too. In fact, I approached Kevin for the first time over a year ago now to see if he would be prepared to take a look at our printing largely because of the hugely in-depth reviews that Mark has carried out on other printers - we wanted to see how we compared. We have also learnt a lot from the approach that Mark has taken to reviewing other printers - as well as the process he put us through, which was extremely rigorous.

I have seen the many comments in the forum relating to the service and wanted to try to respond to as many as possible. I will try to respond to each question or comment in turn, so please forgive me if there is a little bit of repetition. If my answers raise further questions I shall of course be happy to answer them to the best of my, and my team's ability. You can also contact me directly at [email protected].

I will just make a few general comments up front, before I answer specific questions.

The most important point is that we do not want to make greatly exaggerated claims for our technology. We print on the same C-Type paper, and develop using the same chemicals, as any other printer can use (mostly Fuji Crystal Archive DPII papers). We are therefore subject to the same limitations on gamut as anyone else using those papers: the paper itself defines the overall gamut volume and limitations, although how you use that gamut volume (through printer profiling) does allow for some variation between machines and operators. Where we are different is that we have developed an entirely new machine, from the ground up, over a period of over 15 years. The machine was originally developed to solve the problem of how to print extremely sharp text on silver halide - and the precision required to do that also allows us to print extremely sharp photographic images. In my answers below I will try to summarise how we did that and why our approach is different to other machines, and why we call the resultant print the L.Type.

The next thing that makes us different is that we are the only print service in the world that designs and builds its own machines. We don't sell them to anyone else. Instead, we own and operate, maintain and upgrade them all ourselves. The engineers who designed and build the machines run them every day - almost like a racing car team.

I make no claims and take no position for C-Type images against inkjet. As has been made clear in Mark's review and many of the forum comments, modern inkjet printers far surpass C-Type prints in terms of gamut. That's a fact of life about which we can do nothing as we don't make the papers ourselves. Within C-Type gamut (which broadly covers sRGB and Adobe 98 at least), there is a valid discussion to be had as to which approach (C-Type, which is continuous tone, or inkjet, which is a half-tone process) gives the better results. My personal feeling is that this is very much a matter for personal taste. I'd go so far as to say that some images look better in one form, and others in the other - but I don't believe there is a 'right' answer. What we do believe, strongly, is that C-Type prints, properly done, are wonderful - and our aim is to stand at the pinnacle of C-Type printing. Only you, the photographers, can judge whether we are close to achieving that. Giclee prints are also wonderful and will no doubt continue to improve: we just don't see any reason why C-Type development should just stop - there is more to come from that medium.

Finally, I want to say that the people on this forum are unusual. The degree of technical knowledge and expertise here is enormous. I am sure that we have a great deal to learn from you. But you are not necessarily our target market. You know how to profile and operate the best inkjet printers and how to get the best results out of them. You have the time and expertise to evaluate different papers and to compare results. But many photographers do not have that time or expertise - or simply don't want the bother of doing so. We want to offer a service that offers reference standard C-Type printing to those photographers - whether they are among the world's leading pros (we number several Phase One and Hasselblad devotees among our user base) or keen amateur photographers. We want people to know that within our limitations (we only go up to 300mm x 1000mm at this stage) we will always strive to do the very best. We won't alter your images in any way, and we will print what we are sent as well as possible and at a reasonable price, and present them as nicely as we can. I very much hope you will give us a try and would be delighted to welcome any questions or comments from you - especially if they help us improve what we offer. We are on a journey and I hope we will continue to improve over time with your help.

I hope the answers below are useful. Thank you for your interest.
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hrwilliams

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Re: Lumejet Process Overview
« Reply #44 on: March 04, 2018, 05:41:54 PM »

I confess that I did not perform a  DEEP read of this article, but it did not strike me as a particularly new thing at all?

People have been shining colored lights onto silver halide paper to make digital prints for a long time. I don't quite get how Lumejet is any
different from, say, a Durst Theta printer, which has been around for quite a while.

What am I missing?

The essential statement here is correct – and this goes for many other comments made (especially re gamut). We are not doing anything new in terms of the basic principles of shining RGB lights on to silver halide paper, and we are using the same silver halide paper as everyone else. What is different is our focus on the precision with which we do that, both in terms of the physical direction of the light onto the paper, and the control of those light pulses, as well as the way we interact with the paper itself.

There is some (intentionally relatively superficial) description of this at https://www.lumejet.co.uk/technology/. Our technology has been under development since approximately 2000 and many millions of $ (close to $25m) have been spent to date on developing the machine.

Fundamentally, silver halide paper has one basic limitation - the gamut of the paper and the emulsions. This is something we can do relatively little about; we use the best Fuji Crystal Archive Professional DPII papers – their exhibition quality papers – that are available to everyone else (although not all pro labs use these papers, and consumer-oriented labs do not). What we have done ourselves is to re-characterize each media (paper type) using our RGB print head and created bespoke target files for each paper, and then build the best colour profiles we possibly can for our machines.

For the purpose of colour management, a printer must be calibrated to the centre line of the Lab colour space. This calibration produces a neutral Lab grey line from the media white point through to the media black point (DMAX). The calibration provides a repeatable reference point that can be calibrated to before a shift. The reference point is used as the base line foundation upon which the machine’s media colour profile (.icc) is characterised and built.

A media's neutral grey line calibration is specified in the media target (.tgt) file by specifying a number of input R,G,B values and corresponding output C,M,Y colour densities. The target file has a number of incremental steps of input RGB values from white (0xFFFFFF) through grey to black (0x000000). For each step, there is a corresponding output C, M, and Y media colour density that when measured in D50 Lab colour space, produces a Lab neutral colour. When all steps are put together, a Lab neutral grey line is produced by the media. The target file is used by the printer to calibrate the media's DMAX (black). After black calibration, the target file is used to balance the grey to produce the neutral grey line for colour management.

Our target files yield highly accurate neutral LAB gray lines and high DMAX. This is a skilled and ‘black art’ process that few know how to do: Fuji themselves do not do this (or do not share the results if they do), so we had to develop a technique and process in-house to do it ourselves. We believe our target file generation process is very accurate along the whole tone curve and hence we follow the neutral grey line in the 3D gamut. This then gives us the foundation to build our colour profile more precisely through the colour space to the outer edges of our gamut and to determine how we handle out-of-gamut colours.

The key advantage of silver halide is that it is continuous tone. So a single image pixel of any colour is represented on the page by a single pixel of that colour – as opposed to the structured combination of dots of different coloured inks required to create a pixel of a single colour with an inkjet. This does not always matter, but complex effects like subtle split-toning and gentle tonal variation over a page can be very difficult to achieve correctly with inkjet half-tone processes. Halftone is a trick of the eye (side by side dot combinations) that requires a K layer to make up for CMY inks not producing a dense black. Contone is real Newtonian light combination of just CMY dyes as tiny colour filter plates in a vertical stack (dot on dot). And our CMY unit cells are much better aligned, to microns, than the laser and other LED printers, as those were not designed to handle fine text and graphics (requiring 400dpi, the Nyquist minimum for hand held prints). We estimate that inkjet systems would require 12 colours and 10x the pixel density to produce something approaching contone quality .

What really makes the difference with silver halide is how the paper receives light. This is where the majority of our improvement lies. The emulsion layers of the paper contain silver crystals and colour couplers that together, when activated by light, form colour clouds. These clouds are approximately 5 microns in diameter. So the paper is itself capable of resolving extremely small (invisible to the human eye) levels of detail. But this depends on how accurately the paper is imaged. In a traditional darkroom enlarger set-up, light from a small source was beamed through a negative onto paper of the relevant size. The enlargement process caused softening of the image because of the enlargement itself and edge effects as light towards the edge of the paper was not hitting the paper vertically. All silver halide print machines attempt, in various ways, to address this issue – more or less successfully. Some use lasers, some use LEDs, but each of them has imperfections in the accuracy of this imaging process.

We developed the Lumejet printer from scratch over the past 15 years, starting from research projects in Warwick Manufacturing Group’s laboratory in Warwick, UK. The research came about to address the fact that it was then impossible to print sharp text accurately on silver halide. Our printer uses a proprietary print head that incorporates a patented optical fibre taper to reduce an array of 576 individually-addressable RGB LEDs down to a very precise spot. Each LED is 300 microns in diameter, and these are reduced by the optical fibres to 60 microns each. The fibre taper is essentially a pixel projector that takes an array of larger LEDs and produces smaller pixels on the paper to produce ultra-sharp images, text and graphics. The print head is positioned just above the paper and scanned, to micron accuracy, across the paper (like an inkjet with light). As the head passes over the paper, successive RGB LEDs are triggered so that each pixel area on the paper is imaged successively by one LED of each colour, all placed exactly on top of each other. The finished pixel is therefore formed extremely accurately and receives only the light signal from the three R,G,B  LEDs forming that pixel. There is minimal cross-talk between pixels. Because the print head is always directly above the paper, light beams always enter the paper exactly vertically, eliminating edge effects. The motion control and signal processing software that allows each and every pixel to be placed precisely where it should be is highly complex and at the core of our proprietary process. The printer prints 12mm swathes at approximately 1.5m/s across the paper (Y axis) to a pixel placement of c. 1 micron. The paper is then indexed forward by the swathe width (X axis), to a precision of c. 5-7 microns, and the next swathe is printed, with a small overlap (which is blended) to eliminate any motion errors.

So the difference between our technology and other silver halide printers boils down to:
(i)   our pixel is smaller at 63.5 microns (400dpi) - which is the smallest the human eye can resolve for prints held at 14”.
(ii)   our pixels are placed more accurately next door to each other so there is no overlap;
(iii)   the paper is always imaged directly from above so cross-talk between pixels is minimized;
(iv)   we have made a huge investment in calibrating the printer to the latest papers and profiling our printer to ensure that it gets the most out of those papers without compromise. For instance, some other printers will operate at a higher DMax. This produces deeper blacks, but it also causes yellow flaring on whites due to cross-talk and over-exposure. We currently dial back our DMax slightly to eliminate this problem – we believe it is better to have pure greyscales than to push blacks to the max, although we accept that this will not always be optimal. We continue to work on this area and expect to increase DMax progressively over time.
(v)   Our printers are manufactured today by us, and constantly updated – unlike most of the high-end competition that has been discontinued.
(vi)   We are the only photo lab in the world that builds its own printers from scratch, so far as we are aware.


In terms of the more detailed technical differences that make our printer stand out:

Principally it is in the design of the print head, which came about from first principles of physics laid out at the initial Warwick R&D stage more than 15 years ago e.g.
1)   How the 5:1 fibre taper bundle is made and drawn (so there are roughly 300 fibres in front of each LED) and structured, with interstitial black rods between the fibres used to reduce light scatter;

Attached is an image of the top of a tapered fibre bundle:
 

2)   How the fibres are made (by multiple draws of glass with different indices) and the Numerical Aperture of the fibres themselves, to couple the LED light into the fibre internal core, rather than scatter sideways. The NA of our fibres is c. 0.80, which couples light efficiently down the fibre core with little sideways cross-talk, producing a “tapered light funnel” effect in front of each LED with very sharp edges;
3)   How the individual RGB LEDs are robotically placed (to c. 20 microns), wirebonded and aligned on the print head array and exposed through a very accurate and hard edged black mask. This is Gerber plotted at 2400dpi, with precise pitch and interlacing between odd and even rows, to provide c. 10% pixel overlap and avoid micro-banding. We are in fact imaging the mask edges, rather than the LEDs (which vary in size and position);
4)   How the fibres are drawn from 20 microns (top) to 4 microns (bottom), so although we print with a 63.5um (400ppi) spot, the edge of the spot is constrained by the 4 micron fibres at the exit end and gives very little halation (flare, light scatter);
5)   How 4-6 microns is also the grain size of the AgX emulsions – so we are effectively dropping photons on grains (all part of the design); and
6)   How the RGB light at the fibre exit is transferred 1:1 to the paper using a telecentric relay lens (9 stack lens) that has been designed to minimize chromatic aberration (different paths of different wavelengths) and produce parallel light rays into the emulsion.

Sample scans of text and images are shown at https://www.lumejet.co.uk/technology/

Our unit pixel cells are clean with little cross-talk. All of the above design elements were initially addressed and produce really clean, sharp text and graphics: they make for a beautifully sharp photographic reproduction – while older photographic print techniques are inherently less sharp and produce beautiful photos partly through that inherent softness!

To pick up on a few well-known machines:
The Durst Lambda was an RGB laser spinner system, which imaged at 200dpi natively (switchable to 400dpi) and suffered from RGB pixel alignment from middle to edge due to the F-Theta flat field lens (it is also 50” wide). It was aimed at poster making, not small format prints.

The Durst Epsilon and Theta (30”) used multiLED prints heads, imaging at 256dpi, but their LEDs were placed to one side and the light was piped by fibre cables and a large lens onto the paper. Again they were built mainly for images, not text and graphics, and the final beam shaping/delivery was not done as LumeJet.

Other machines are also very good, but none was designed to print text and therefore all suffer from some compromises in sharpness and accuracy relative to our machine.
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hrwilliams

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Re: Lumejet Process Overview
« Reply #45 on: March 04, 2018, 05:46:48 PM »

Thanks for the perspective.

I guess as one who has owned and operated LED based silver halide printers for over 20 years (my first one was the Kodak "Pegasus" LED printer which produced pretty remarkable results), I just don't see this as a new process. I think those that have never seen many digital C prints are surprised that the "limited" gamut and "meager" 300 dpi resolution can result in very sharp prints with great saturation, smooth gradations,  and visually very competitive with high end inkjet prints.

So my curiosity is piqued ... have they really managed to improve the digital c print over previous technologies. Are they going to manufacture and sell the device to other labs? (seems that's would be their main goal, to market the technology). If you and Kevin can figure out how to test that it would be very enlightening.

I think I have essentially covered this above. What we call the L.Type is generically still a C-Type print. We use the same papers and same chemicals as others. But we use completely different equipment to image that paper compared with what anyone else does.

The easiest way to see how we are different is to look at our text. This is much sharper than text on other silver halide printers and has regularly beaten litho/ Indigo in commercial tests by prospective customers. The pixel control and sharpness that is demonstrated by our text printing carries over into our photo printing – it’s the same thing.

To answer the specific point about manufacturing/ selling the device/ technology: the answer is 'no' - we do not want to sell it at all. To be frank, our machine is slow. And in a world where everyone is obsessed with building faster and faster machines - particularly in silver halide printing - the economics of running a machine slowly to try to make a better print are not attractive to most labs. So we think that a more sustainable business model for us is to operate all the machines in existence ourselves and keep upgrading and developing them as we go. Every time a customer suggests something that could improve - or has gone wrong - we try to learn from it. But if we continue to operate all the machines ourselves, speed is much less of an issue - and that allows us, we think, to produce better prints.
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hrwilliams

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Re: Lumejet Process Overview
« Reply #46 on: March 04, 2018, 05:53:45 PM »

Let's not forget process control (consistency in output over time). I'm sure Wayne can tell us how much work it takes from the printers owner's end. But the end user expects (or should expect) the RGB values he output's today and in a year will look identical. And that's easy with modern ink jet printers. What's the dE drift when sending out colors today and in a month? Or among a lab using more than one machine. Again, with a modern ink jet (certainly Epson's and I've got plenty of colorimetric trending data), the differences are not visible.

That sounds like marketing speak! If you send the IDENTICAL set of patches (and 31 is rather tiny) through a Spectrophotometer, you'll NEVER get a dE of 0.00! Impossible. There's noise in the individual readings of the same two sets of patches. Had the Marketing department who made this claim understood such a fact, they would have stated something like 0.04 or something like that (be happy to upload an actual colorimetric report of dE differences measuring the SAME target twice in a row).

This is a very good point. We do everything we can to address this. From profiling our machines; calibration every shift, every new roll; colour process control checking after calibration and monitored during the shift; common chemical reservoirs so all machines are fed identical chemical mixes; precise temperature controls on the processors so all processing takes place in tight tolerance; etc. We use the 31-patch test scan on each order and record those values and will try to provide you with some data over time, though please be aware that that process has been in use for less than a year. The 31 patches, which are the CC24 Lab patches with 6 extra gray scale patches and a media white patch) are all known LAB values and printed absolute colorimetric then measured independently using basICColor software to validate the repeatability and accuracy of the process using a deltaE 2000 measurement.

The accuracy of the prints is being measured against a fixed absolute that is the same for every printer. We believe we hold best-in-class accuracy and it compares well with professional inkjets on each and every job.

I think Mark has addressed the marketing speak point above - we absolutely don't claim a dE(2000) value of 0. That's clearly impossible. As you rightly state, even scanning the same strip twice produces variation in the results. Part of that in fact is because the profiler we use to scan marks the paper, so it can't be scanned again on the identical line, and part of it is because of the natural error in the scanner. But we claim to be broadly in the range of 0.6-0.9 dE(2000) on average across the 31 patches on each print we make and we reject any print with dEs on any individual patch that would provide a visible difference between target and actual output. We believe this is highly competitive against even the best inkjets when they are properly profiled and properly used, particularly impressive in comparison to other silver halide printing, and certainly likely to beat any printer that is not properly profiled/ used/ maintained - which should be one reason why the average user chooses a service like ours.
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Kevin Raber

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Re: Lumejet Process Overview
« Reply #47 on: March 04, 2018, 05:54:21 PM »

Huw, Thanks for all the detailed information.  I also will have a video and report on my experience with the L.Type prints published very soon.  I was quite impressed and I think the article and video will explain things more clearly too.  Stay tuned.
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Kevin Raber
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hrwilliams

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Re: Lumejet Process Overview
« Reply #48 on: March 04, 2018, 05:55:30 PM »

Mark,
What interests me more than the C-prints is their "photobook printing". At present, they ask clients to use In Design instead of providing a template of their own and only create the book block which needs to then be sent to a binder. The description sounds like it may be an improvement over the quality produced by most online photobook producers. From my discussion with them by e-mail, I've learned that Kevin may be using this service. It would be helpful to a lot of us if an evaluation of this product could be made. Even if it is subjective as opposed to time-intense objective testing.

We aren’t desktop publishers – we are set up to print finished files that photographers and commercial designers send us and we typically take in either Indesign files or print-ready pdfs. Having said that, we are working hard to produce a simple bookmaker on our mobile app that will make it easy for the average photographer to produce a good basic layout that will cover 90% of situations. My guess is this is 3  months away but we are working on it.

Kenneth, you and I have exchanged emails as you mentioned - and I'd be delighted to print a test book for you if you would like to send us some images.
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hrwilliams

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Re: Lumejet Process Overview
« Reply #49 on: March 04, 2018, 06:02:05 PM »

It's always interesting to hear of new print services. I'll probably give them a spin, although I too am puzzled as to whether they are offering anything radically different from Lightjet or Lambda printing (which are well-catered for here in London). They operate from an industrial estate in Coventry, so I guess it's mail-order only. And their maximum print width seems to be 30cm (up to 100cm long) – so no exhibition prints, just books and (small) portfolios. To their credit, they've garnered some good testimonials. It's rather confusing that they have two websites:

http://www.l-type.com/
https://www.lumejet.com/


It is hard to argue that we are radically different. But people pay good money for incremental changes. Our printer is quite simply the latest and the best developed in the silver halide world and produces the best results. On the other hand, it has clear format limitations that the Lightjet or Lambda don’t – so for larger format prints they will remain an appropriate solution.

We are primarily internet-based, though we are always very happy to see photographers and anyone can visit any time. We often host educational tours for students, too.

Your point about websites is well made. Our first website was www.lumejet.com and this was based on a ROES-type platform that allowed print uploads and a modicum of editing. I would say that this is very much a consumer-oriented approach. We found, however, that the vast majority of our users preferred not to have to upload their prints individually before placing an order - most people seem to prefer to use Wetransfer, or Dropbox or some similar storage mechanism and just to send us a link to their files. So L-Type.com was designed as the site that tells our story, shows what we can do, and essentially allows you to send us the files in any way you want to get them to us. After that, we take your files, follow your instructions, prepare a contact sheet for approval and send a payment link before printing - we know this takes a bit longer, but it seems to give better results in most cases. If you want a fire-and-forget solution we have just launched an iOS app (iOS only, I'm afraid) that is on the App Store under L.TYPE PRO PHOTO PRINTS. This integrates with Dropbox and allows you to order high-res images using your mobile device as a 'remote controller'. The images need to be in a Dropbox folder (we hope to add other integrations soon) but assuming you use Dropbox, an order can be completed in less than 60 seconds if you are familiar with the app and it gives you full preview/ cropping/ re-centering capabilty.
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hrwilliams

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Re: Lumejet Process Overview
« Reply #50 on: March 04, 2018, 06:06:42 PM »

Be kind of interesting to have them output actual targets of a lot more color patches over time and measure them independently.

I will try to get you some time-based data, though bear in mind that we have only been undertaking this measurement for a few months.

We could of course add more patches, but X-Rite, FOGRA, etc all use a limited number from across the spectrum and this seems a reasonable approach. Adding more patches just means a larger area of paper will be wasted with every print. I’ve addressed the matter of measurements over time.

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hrwilliams

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Re: Lumejet Process Overview
« Reply #51 on: March 04, 2018, 06:13:35 PM »

I am posting this at the risk of revealing myself to be a member of an apparently tiny minority of Lula members who do not own nor plan to own an inkjet printer.

I certainly would love to have the superior color gamut of inkjet pigment printing, the print longevity, the apparent detail; but also the smoothness and seemingly infinite detail of the N-surface paper from large format film, and for it not to cost a fortune, and for the prints not to be damaged by a slip of the finger.

I don't have the room to house a top quality inkjet printer nor the patience to deal with various necessities for getting excellent prints (calibrating the printer, different profiles for each paper, keeping them in sync and up-todate, dealing with machine maintenance and periodic problems, and so on). 

Those inkjet labs that I have tried either did not offer printing on papers that interested me for most purposes (e.g. WhiteWall) or others that I tried were too expensive,  and the quality of output that varied from mediocre to poor.

What I would like to find is a printing process that will give me the quality I found so attractive with color prints made on N surface paper from large format film, yet to have that with photos now taken with full-frame or small medium format size cameras. I like to look at a print with the proverbial nose to the print. Not a practical way of looking, but that's what floats my last-century boat :-).

I'm sure inkjet printing has improved since I last tried, but I don't know what labs I should consider, nor the exact paper surface  (although come to think of it there is probably plenty of info on appropriate papers already here on Lula).

I am interested in the Lumjet printing process and also am a little bit interested with WhiteWall's so-called HD process (although WhiteWall offers their 400 PPI process only on glossy paper which I generally don't like).  Lumjet offers various papers types including a type of Matte which might be what I'm looking for.

While the Lumjet process may not interest the vast majority of those here, I am glad the article was published, and I may give Lumjet a try.  While it doesn't seem like Lumjet would fulfill all my needs (restriction on sizes, mounting options), at least it may be useful for some of my purposes, and also perhaps for at least a few others here on Lula.  Even if not,  I personally find it interesting to read in detail about improved processes.

My thanks to Mark Segal, and also to Kevin.

Dan

P.S. Hey, I love those posting verification questions. But arithmetic is just so last-century. How about some questions involving calculus, or quantum mechanics. I need something to challenge my aging and increasingly lazy brain :-)

Dan, thank you for your first few sentences.... you are the customer we're trying to support ;)

Re Whitewall, I don’t know anything about the WhiteWall HD process. I believe it is done on a Polielettronica machine. It claims a 600dpi print density (but we believe this is really a 300dpi machine interlacing up to 610dpi – older LaserLabs had resolutions of 254 and 305 dpi - but this may be wrong), but there are a couple of important caveats to that:
(i) pixel placement without overlap is key – and that is core to our approach and hard to achieve with lasers from a central source;
(ii) there are good technical reasons why making your resolution too fine may not work: the real issue is that AgX photopapers start to fall off in resolving power above c. 450dpi (the so called Modulation Transfer Function roll off point), so there is no real benefit to imaging at great resolution. It will depend also on the beam shape and how the RGB pixels hit the paper one on top of the other. With laser spinners they suffer from jigger (gets worse as they age) and the FTheta lenses (flat field correction lens that takes the spinner's RGB laser parabolas and tries to create a ‘flat field’ across the paper width) are not precisely flat field, particularly at the edges, and suffer from chromatic aberration – different paths taken by different wavelengths. This has been confirmed to us by a major manufacturer, particularly for widths greater than 12";
(iii) 600dpi is way smaller than the eye can see.  At 600 pixels per inch, you could fit an entire 70MP file on a piece of paper approx. 16”x12” pixel-for-pixel so this is possibly of interest for printing small images, but irrelevant for large images as you would have to ‘invent’ additional image data to get to any larger format at all.

Having said that, other elements of the Whitewall process accord very closely with our own approach - thinking about how you store paper, for example, and deep attention to all the details of chemistry and every other process step so as to get the best possible result. Whitewall are a superb outfit with a great reputation.
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hrwilliams

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Re: Lumejet Process Overview
« Reply #52 on: March 04, 2018, 06:16:42 PM »

Ok, so I am taking another swing at this thing, even though color science makes me all cross-eyed. I'm kind of getting lost in the technicals.

"Every pixel is created as a unique exposure for every one of the 576 RGB LEDs. This is finely controlled by digital circuits that give 2048 grey levels/pixel for Red and Green and 1024 levels for Blue (32bit levels). The individual RGB exposures for each of the 576 LEDs are delivered down the fiber taper and projected in parallel so that they image vertically onto the paper."

Does the print head do 576 pixels in one go, and then go on to the next 576 pixels? Or are all 576 LEDs involved in each pixel? Or, um, is it actually 192 S, 192Gs and 192Bs, doing 192 pixels at a go, or what? The first sentence seems to have been mangled, or maybe I am just persistently not reading it the way it's intended. Either way I cannot make any sense out of what it means.

Slightly later we find:

"4 billion unique colors possible for each printed pixel"

Is this even meaningful? I mean, it sounds sexy, but I'm pretty sure that's orders of magnitude more colors than we can see?

I feel like I could make sense of the analysis of the results, and I understand the bit at the end "these things look good", but the description of Lumejet's process is still pretty opaque.

Also, I have to say that Lumejet's quotation of pixel density in  squares rather than lines (160K vs 90K) sounds disingenuous, albeit accurate. When you state it as 400dpi vs 300dpi it doesn't sound like Lumejet has such an advantage. If they stuck with it, I might let it slide, but literally every other reference is to 400dpi. It's only when they want to seem bigger that they go with the square.

Just for humor, imagine this sentence:

"As a result of this, LumeJet claims that its 400dpi print quality is greater than that of multi-colour inkjet printing at over 4000dpi."

re-written as:

"As a result, Lumejet claims that it's 160K pixels/sqinch print quality is greater than that of multi-colour inkjet printing at over 16M pixels/squinch"

which, while it says exactly the same thing, feels a heck of a lot less convincing.

576 LEDs in the print head is actually 192 each of 3 colours (R, G, B). Each printed pixel will contain light only from 1R, 1G, 1B LEDs. We use the terms pixel and dot interchangeably because ideally we will print an image at a native 400 image pixels per inch – each image pixel will be represented by one printed pixel, and that in turn will have received 3 light pulses. The scanning head lays down 192 red pulses at a time, and passes on over the page. Behind it comes a row of green LEDs, and so on. So each pixel is imaged 3 times, very accurately, in turn.

There is a perfectly valid question about the use of the figure of 4 billion colours. There is a wide range of estimates of how many colours people can see – anywhere from 1 million to 14 million – though I’m not sure we know whether the ones I see are identical to the same number you see. So it is absolutely questionable whether printing above 8-bit levels (which gives 16.8 million combinations) is relevant to any printer, though everyone is trying to beat that. The main purpose of such fine distinction between pixels is to maintain a very smooth,  gentle tonal gradation across a page without any banding or granularity or other effects. So long as the differences between pixels are not visible to the eye, then the resultant image will appear incredibly smooth. Vignettes and sweeps require this tonal range to avoid density breaks, also smooth transitions into catch-light and catch-dark – shine on metallics, filigree in dresses, et al. A huge proportion of the detail and modelling lies in the very light and very dark areas, which halftone naturally drops out – and we increase the amount of tone data in these regions to try to capture this. We were reviewed by Joel Tjintjelaar of bwvision.com, who is an incredibly exacting and demanding photographer and he said he had never seen printing as good as ours for split tones on B&W photography.

One of the other points related to our use of the maths of 400dpi = 160k pixels/ square inch vs 300dpi = 90k pixels per square inch. Again, we need to be clear. We use ‘dpi’ and ‘ppi’ interchangeably. Because, as stated above, one input pixel from the RIP becomes one pixel on the page. In an ideal world, one image pixel from the original camera sensor becomes one pixel on the page (ie there is no rescaling/ resampling anywhere). Then what we print is exactly what was captured. Taking this comparison and applying it to the 4000dpi of an inkjet (and then squaring it up for area) is unfair - because our 400x400 pixels can represent 400x400 image pixels. Whereas an inkjet printer at 4000dpi would use 16 million dots of ink to represent the same 160k image pixels.

We are trying to produce prints that have all of the detail that the young human eye can resolve at arm’s length. Other printers are good for greater distances and larger sizes. We want our prints to be held close and examined closely. So, as mentioned earlier, we chose a resolution that is as small (c 60 microns) as the human eye can see. This is the 400dpi/ ppi figure. This in turn, as a simple statement of maths, implies that we take 160k image pixels and put them on 1 square inch of paper. So a 16x12” paper holds approximately 31MP
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hrwilliams

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Re: Lumejet Process Overview
« Reply #53 on: March 04, 2018, 06:17:56 PM »

Given that their maximum print width is 12 inches, is it safe to assume they are using some sort of minilab (Fuji Frontier, Noritsu etc)?

No. Our machines are completely different to anyone else’s. They are built by us from the ground up. It happens that today we can only do 12 inches. This is, frankly, because our paper handling needs to be so incredibly accurate that we can only currently manage it at 12” width. We want to introduce larger machines but they will probably work on different principles (fixed paper, scanning head) to avoid twisting/ movement of the paper in any way.
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hrwilliams

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Re: Lumejet Process Overview
« Reply #54 on: March 04, 2018, 06:18:18 PM »

The LED counts only affect the end user if banding is visible when the machine does not expose and advance precisely. Trust that the machine works.

What is more important and easier to understand is, the machine can (or should as many others already do) print pixel-for-pixel from 400 ppi files. Although their website says one cannot see the individual pixels, I'm sure they are mistaken. All these machines easily print discernible individual pixels when the test is provided. Single red, green, blue pixels on white, gray, and black backgrounds are easy to see with a loupe of 8~12 power. Single pixels on white are to be found on ink jets, not so easy to see on gray or black backgrounds. Pixels subsampling is employed also. Lenses may be used also. Common lenses such as Nikon in the case of Chromira LED printers. Thus a digital enlarger exposing typical color photo print material. Awesome, still.


I am not sure I quite understand this point. If you were to print a single pixel in the middle of a piece of paper you could indeed see it – certainly with a loupe - because it would stand out from the background. Just as you can see a line printed on our machine that is only a single pixel wide. In fact, I’d go further. We can print a single pixel of ANY colour (in our gamut) as a single dot on the page. That dot will be made up of 3 layers of dots in the emulsion, but even under magnification you will only see one dot. Contrast this with an inkjet that must, by definition, place multiple dots of ink of different colours to create one pixel unless that pixel happens to be exactly the colour of one of the inks.

But if you consider an image made up of many pixels, then you cannot see the pixel structure in an L.Type print in any way with the naked eye although you CAN see all of the detail in the image with great sharpness. All you can see under a Loupe is a very faint regular grid pattern – which speaks to the accuracy of the positioning of all the pixels. Under a loupe, an adult will probably find that new detail is revealed because their eyes aren’t quite good enough to resolve it. A younger pair of eyes should be able to see it all, but 400ppi/ 64 microns is pretty much the limit and we see no point in going finer.
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hrwilliams

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Re: Lumejet Process Overview
« Reply #55 on: March 04, 2018, 06:18:45 PM »

Yeah,  I get that they're printing dots at 400dpi, but I feel like if you're going to include a paragraph on the 576 LEDs then I ought to
be able to work out what the paragraph means, you know?

In a sense the 576 LEDs is a red herring. The figure could be 30,000 LEDs and all that would tell you is the width of the swathe we print at one time. So 576 LEDs = 192 pixels wide (3 colours for each) = 12.2mm wide swathe printed each time. We print, move the paper, print, move the paper, and so on…just like an inkjet.

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digitaldog

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Re: Lumejet Process Overview
« Reply #56 on: March 04, 2018, 06:31:39 PM »

There is a wide range of estimates of how many colours people can see – anywhere from 1 million to 14 million – though I’m not sure we know whether the ones I see are identical to the same number you see. So it is absolutely questionable whether printing above 8-bit levels (which gives 16.8 million combinations) is relevant to any printer, though everyone is trying to beat that.
I've generally heard about 12 million but the point is, it's not anything like 16.7 or billions: IF you can't see it, it's not a color. So the bit (no pun intended) about such massive numbers of device values is, they are all not all colors (assuming we agree upon 12 million and marketing states billions, there's more we can't see than we can by a massive margin). Yet marketing from many, many companies keep trying to get customers to believe more is better. As for billions of device values, I'd be love anyone to demonstrate on a print that has more than 8-bits per color encoding of image data AFTER editing versus the high bit version produces any visual difference on the print. Bit depth is about editing overhead and again, I'd love to see someone demonstrate on a print, even with fine gradations that more than 8-bits per color of a final edited image is inferior to sending a higher bit cousin. 
« Last Edit: March 05, 2018, 10:46:57 AM by digitaldog »
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Andrew Rodney
Author “Color Management for Photographers"

amolitor

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Re: Lumejet Process Overview
« Reply #57 on: March 04, 2018, 08:46:44 PM »

Thanks, Huw. That was very informative, I appreciate you taking the time.
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elliot_n

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Re: Lumejet Process Overview
« Reply #58 on: March 04, 2018, 08:57:08 PM »

Indeed. I look forward to trying the service.
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Stephen Ray

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Re: Lumejet Process Overview
« Reply #59 on: March 05, 2018, 03:05:05 AM »

Quote
Quote from: Stephen Ray on February 26, 2018, 08:45:56 PM
The LED counts only affect the end user if banding is visible when the machine does not expose and advance precisely. Trust that the machine works.

What is more important and easier to understand is, the machine can (or should as many others already do) print pixel-for-pixel from 400 ppi files. Although their website says one cannot see the individual pixels, I'm sure they are mistaken. All these machines easily print discernible individual pixels when the test is provided. Single red, green, blue pixels on white, gray, and black backgrounds are easy to see with a loupe of 8~12 power. Single pixels on white are to be found on ink jets, not so easy to see on gray or black backgrounds. Pixels subsampling is employed also. Lenses may be used also. Common lenses such as Nikon in the case of Chromira LED printers. Thus a digital enlarger exposing typical color photo print material. Awesome, still.

I am not sure I quite understand this point. If you were to print a single pixel in the middle of a piece of paper you could indeed see it – certainly with a loupe - because it would stand out from the background.

Yes Huw, my point being exactly as you have described.

Individual pixels are easily discernible because the machines can be that accurate. The small test patches as I have described can verify that and were always a common test for any digital enlarger upon a machine install or after service. Practically all machines could satisfactorily pass the test from edge-to-edge. Lambda, LightJet, Chromira, Politechnica, Fuji, Noritsu, Kodak, are the brands I was familiar with. The machine I have used were high volume work horses that were extremely stable in regards to beam focus. (Years.)
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