June 2013 - colorsync-users

Re: Colorimetric Accuracy in the Field
by iain＠matrixcolour.co.uk 08 Jun '13

08 Jun '13

HelloI hope this gets through. Im not sure how to reply to the list. Interesting thread. Define colormetric accuracy – Colour in equals colour out? Colour in depends on illumination, spectral response of surface (we will take surfaces as example) and an observer, in this case 2˙ standard.(Not forgetting this also depends on instrumentation accuracy – traceability to national standards – and repeatability).And as Jeffrey suggests are we all standard 2˙? but thats another debate. I think there is a new research on redefing the standard observer for different age groups and using sharpened cone responses to produce a new set of CMFs. We can now define our subject in terms of colormetric input. ie we have measured our Colorchecker SG ten times and went outside taken a pic noting the SPD of the daylight using your Minolta CS1000 exactly at the time of exposure. And this is the bit I think is in question. Is the scene captured by the camera an accurate colormetric representation? This depends on how the device values are converted to CIEXYZ. This is the bit that make everything colormetric accurate or not. There are two main methods for calculating the transforms (camera matrix) to produce scene colorimetry estimates from sensor data. The first is a target based method (using Macbeth Color Checker for instance) and the second is to use spectral colours produced by a monochromator (the latter my preferred method). Currently the approach used by both methods for error minimization is to calculate the RMS error in CIEXYZ, CIE L*a*b*, CIE L* u* v* or in a linear or non-linear based RGB space (ITU-RBT.709, RIMM RGB). It is this matrix and how it is made and its performance which will define wether you have colormetric accuracy. And as the camera CMFs are not exactly the same as standard 2˙ CMFs there will be errors. It is not easy to test wether the matrix you have used in your raw converter is accuarte or not with out a lot of meassuring, shooting and comparing values. But you have the rendered image of the colorchecker SG and you can open an save in prophoto and convert back to LAB and compare measurements. I would rather have the CIEXYZ produced by the raw convertor to check the accuracy but few give this.It the raw converters let the user access the matrix then that would be different. If you did deep enough into DCRAW Ccode you will find the matrixses. What happens after rendering from CIEXYZ to say sRGb , ProPhoto to CMYK etc is anyones guess, it up to the user and the control on the raw converter or what ever software used. All accuracy is then a matter of choice and gamut constraints. But as the OP asked about "colormetric accuracy", I think it boils down to that precise device characterization is essential in order to produce acceptable scene referred colorimetry. ie device values to CIEXYZ with minimum errors. Iain

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i1Pro2 - is there a ColorPicker replacement?
by Bruce Andrew Jamieson 06 Jun '13

06 Jun '13

Hey, everyone! I just bought an i1pro2, replacing our old SpectroScan and ProfileMaker Pro. I was used to being able to take readings of all sorts of objects (not just charts) with the ColorPicker module and exporting spectral data, Lab colors, Photoshop palettes or a number of other formats with ColorPicker, a module in ProfileMaker Pro, with which I would imagine many of you would be fairly well acquainted. I'm looking for something that updates/replaces ColorPicker, and I've been a little let down with what comes with the i1pro2. I see that I can do something kinda like it by telling it to measure a chart, but I have to pre-define how many colors I'd like to measure and I have only one very basic export option for a text document of Lab colors. Not very wieldy. There is also Pantone's Color Manager which doesn't give Lab data at all. Pretty, but not what I'm looking for. There is also the option of running my new i1pro2 with ColorPicker itself, but I'm running out of computers running Mac OS 10.6 or earlier! Also, ColorPicker doesn't take advantage of the M0, M1 and M2 measurement modes and requires a dongle for saving. Is there a tool that does the exact same thing as ColorPicker but something I can run on Mac OS 10.7 or 10.8? Thanks, Bruce Jamieson

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Re: Colorimetric Accuracy in the Field
by Ken Fleisher 06 Jun '13

06 Jun '13

If you don't feel like reading the entire thesis, there is a partial summary of it's contents in this blog: http://johnthemathguy.blogspot.com/2013/05/is-your-green-same-as-my-green.h… On Thu, Jun 6, 2013 at 2:04 PM, Lars Borg <borg(a)adobe.com> wrote: > > PS. Just after finishing this message, in my inbox arrives a paper titled > "COLOURIMETRIC OBSERVER CATEGORIES AND THEIR APPLICATIONS IN COLOUR AND > VISION SCIENCES" by Sarkar, A., Blondé, L. > What a coincidence! >

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Re: Colorimetric Accuracy in the Field
by David Ramsey 06 Jun '13

06 Jun '13

Greetings I too have been following this conversation and it has been fascinating and informative. I come to this party somewhat in the middle. I am not a color geek but I am a commercial photographer who's clients expect a certain level of color accuracy. This includes manufacturers, ad agencies, as well as various museums/artists/galleries. They want to know that when I hand them a file it will reproduce (printing, web, etc.) properly. It seems to me that one should "start' with an accurate color representation of whatever they are photographing and then go from there. When I began photography the first thing my instructors had us do was learn the zone system, proper file development, proper printing techniques, etc. After these skills were mastered we could then "break" the rules and make art. We had to crawl before we could walk. Beginning ceramic artists/potters who want to make pots like Byron Temple still learn the basics first - throwing cylinder after cylinder. I don't understand why but a Nikon nef file opened in NIkon Capture NX2 will, out of the box, have better, more accurate color than ACR. I understand that this is a subjective statement but I have had this discussion with many photographers who use Nikon gear and all are in agreement. The downside is that NC2 is so clunky that it is virtually useless in a commercial workflow. So ACR it is, but there is something going on under the hood(s) that I have been unable to resolve. Digital photography has come a long way and I look forward to what's to come. Great discussion! BTY, Was David's (the original poster) initial question was ever answered? Regards David Ramsey

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Re: RPP raw photo processor 64
by Henry Davis 06 Jun '13

06 Jun '13

Andrew - I'm just catching up on this thread and have found it interesting. Your response to Ben about white balance on the beach at sunset causes me to ask if there's some "native reference" or starting point for white balance. What happens when a white balance is made? I know what it attempts to do but I don't understand how it goes about it. Is there a null white balance or table of some sort or is there a common one assumed such as daylight and the new balance adjusts that? You're right that the cast would get screwed up if white balance is applied to the beach scene. Prints made from color neg film were all over the place with this kind of scene but some were actually pretty darn good. Was it strictly a difference in the creativity of the photographer and print maker or was there a technical approach that could be repeated with accuracy? This business about the illuminant must be central to colorimetric issues and it would be interesting to know more about it. It seems to me that when filters/sensors are designed there must be assumptions made that characterize the incoming light and this can't be gotten around when trying for colorimetric matches. I believe it would take a spectral approach for colorimetric matching but it wouldn't be possible to make a print that verified it. This would only be verifiable by the numbers - not visually. Well, that's what I believe anyhow. Ben - I read your statement differently I guess, and so my answer would be: the camera imposes an inherent error. The colorimetric problem starts there, in the camera. I don't know if a sensor or combination of filters can be made that would make a colorimetric match possible. On the other hand, they sometimes do a pretty good job of matching paint at the paint store. Henry Message: 7 Date: Sun, 02 Jun 2013 10:29:24 -0600 From: Andrew Rodney <andrew(a)digitaldog.net> To: "colorsync-users(a)lists.apple.com List" <colorsync-users(a)lists.apple.com> Subject: Re: RPP raw photo processor 64 Message-ID: <55224C4F-E1E0-4F46-A9E0-0507CE268C27(a)digitaldog.net> Content-Type: text/plain; charset=us-ascii <Snip> Ben: > Improper white balance and exposure are colorimetric failures Andrew: Well it certainly isn't a recommend photographic workflow to improperly white balance and improperly expose! If I white balance a scene of a model on the beach at sunset, is that colorimetric failures? It would certainly produce an image that doesn't look anything like the original scene.

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Colorimetric Accuracy in the Field
by Henry Davis 06 Jun '13

06 Jun '13

Terry - You've been in the profiling arena for a long time so I believe that you already know what you're going to encounter if you're about to get into art reproduction. I apologize for not making the distinction in earlier posts but I'm still a little reluctant to dogmatically say that a colorimetric "match" in the field isn't a worthwhile challenge too. But, my interest in this thread is mainly over art repro and I'll try to make that clear in future posts. I think that the variables in field will be a side challenge, important considerations - but not something that should cause one to dismiss a colorimetric approach in the field. Nature throws curve balls and so do paints and other materials used in artwork. But it seems that at least some of the limitations for colorimetric work could have been addressed and worked out a long time ago as profiling and the ICC initiative began. I believe the focus on color management for big software companies and printing companies took the ball and defined the game - but that's just me doing speculation. Anyhow, colorimetric matching just didn't get done. I guess Rodney's point about there being very little interest in the approach had a lot of weight in the beginning and it's still a factor. I've made ICC profiles under studio conditions for every shot I've made of art and printer profiles aplenty but I've been overall disappointed. Not disappointed in the concept but disappointed in the colorimetric failures and how close it seemed that it could be accomplished if only there was something else. Some results still tell me loud and clear that I'm better off without profiling - just taking what the camera gives me. When ACR first appeared I was excited that this might be helpful for art repro. I combined ICC profiles and ACR and was sometimes pleased (but never extremely pleased) but it seemed like there was something in ACR that wouldn't get out of the way. Because I followed him since my Quark days I worked out Bruce F's ACR approach for studio work but it didn't get me there. I've read everything I could that Robin has offered and believe that his explanations put light on some very important things to consider. I've read all that Bruce L has offered and appreciate his helpful ideas. Then came this RPP thing and it got me hopeful again and a little stirred up about the subject. It seems to me that regardless of the size of the audience there's something valuable about the pursuit. Perhaps it may result in even producing something of value for those who have no present interest in colorimetric matching. Even if it's just hangar flying. Henry

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Colorimetric Accuracy in the Field
by iain＠matrixcolour.co.uk 05 Jun '13

05 Jun '13

HiThis may be of interest re colormetric accuracy and colour appearance in digital photography.I published it a few years ago. https://dl.dropboxusercontent.com/u/90361226/ICIS%20PAPER%20274%20.pdf Iain

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Re: Colorimetric Accuracy in the Field
by iain＠matrixcolour.co.uk 05 Jun '13

05 Jun '13

Hi This may be of interest re colormetric accuracy and colour appearance in digital photography.I published that a few years ago. https://dl.dropboxusercontent.com/u/90361226/ICIS%20PAPER%20274%20.pdf Iain

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Re: Colorimetric Accuracy in the Field
by Henry Davis 05 Jun '13

05 Jun '13

Andrew asks: "If I measure the illuminant and the scene, then I measure something in the scene, then reproduce those identical colors onto some device, is that colorimetric accuracy?" You ask a great question and I have to ask: Are you not MEASURING the reproduction? In the past you have used dE as both a sword and a shield. So, my question is this: Is the weight to go to machine- measured colorimetry or perception? It seems to me that your position has evolved over the years to a place that's undefined. You seem to want it both ways - which I believe is also true of the ICC initiative from the get-go. So, which is it? How is color accuracy now defined a la Andrew? Henry

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AccuRaw
by Rich Wagner 05 Jun '13

05 Jun '13

A new Mac (OS 10.7, 10.8) raw processing program was recently released that claims a "100% accurate color workflow." Anyone have any experience with this? "AccuRaw has a 100% accurate color workflow end to end, and lets you explicitly select whether or not to use tone curves, highlight preservation, etc, etc. And of course, AccuRaw supports industry standard DCP (DNG camera profile) camera calibration files as produced by software from many vendors." The author is Alexander McGuffog - related to Sandy McGuffog of dcpTool fame? If the marketing claims are true, it would dispel the notion that "accuracy" is not possible using DNG profiles. https://itunes.apple.com/us/app/accuraw/id587280529?mt=12 https://sites.google.com/site/accuraw/home --Rich Wagner

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