Re: Art Duplication
Re: Art Duplication
- Subject: Re: Art Duplication
- From: Don Hutcheson <email@hidden>
- Date: Fri, 18 Sep 2015 20:16:58 -0400
You’re suffering from two main issues:
1. Metamerism failure - the colorChecker's pigments have no specific correlation to oil paints. This is exacerbated by your use of flash, which is a highly spikey light source, quite removed from the relatively smooth and continuous curves of D-50 and most standard lighting booths.
2. Profile creation software that’s aimed at pleasing color, not accurate color reproduction.
Of all the art galleries I’ve trained to do art capture, the most successful (by far) were those I persuaded to use plain old hot, inefficient, but beautifully continuous-spectrum tungsten or halogen bulbs, suitably heat-filtered to avoid melting too much paint!
And IMO the best camera profiling software for art capture is STILL MonacoPROFILER (R.I.P.) if you can get hold of it.
Having said that, even with tungsten and a Monaco profile, Metamerism failure is still an inescapable reality, but your starting point would be much closer to a “Match”.
FWIW
........................................................
Don Hutcheson, President
HutchColor, LLC
Washington, NJ USA
email@hidden
M: 908-500-0341
........................................................
On Sep 18, 2015, at 19:35 , email@hidden wrote:
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> Today's Topics:
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> 1. Re: Art Duplication (Spinnaker Photo Imaging Center)
> 2. Re: Colorsync-users Digest, Vol 12, Issue 114
> (Millers' Photography L.L.C.)
> 3. Re: Art Duplication (Ben Goren)
> 4. Re: Art Duplication (Spinnaker Photo Imaging Center)
> 5. Re: Art Duplication (Ben Goren)
> 6. Re: Art Duplication (Robin Myers)
> 7. Re: Art Duplication (Ben Goren)
> 8. Re: Art Duplication (Spinnaker Photo Imaging Center)
> 9. Re: Art Duplication (Ben Goren)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 18 Sep 2015 12:25:06 -0700
> From: Spinnaker Photo Imaging Center
> <email@hidden>
> To: Louis Dina <email@hidden>, email@hidden, email@hidden,
> John Castronovo <email@hidden>, Andrew Rodney
> <email@hidden>
> Cc: colorsync-users <email@hidden>
> Subject: Re: Art Duplication
> Message-ID: <email@hidden>
> Content-Type: text/plain; charset=utf-8
>
> I thank everyone for their information and education.
>
> I use the Paul C. Buff, White-lightning Ultra1800, each flash tube is UV coated. Reflectors are 7 inches. Polarizing filter sheets are over each reflector.
>
> A Schneider B+W UV-IR-CUT filter is mounted first on EF 100 mm f/2.8 Micro L lens, and finally the circular polarizing filter.
>
> I might just see where some of my issues come in. Could it be the cardboard x-rite CC? (I refuse to use the passport CC).
>
> Workflow is camera white balanced with what is supposed to be a white target on one side, and black, gray, and white on the other side. These three shades are for me to determine, exposure. Then, I use the white only side to determine white balance in camera.
>
> Next I image the x-rite cardboard CC. Though, sometimes I have the cardboard CC included in the area along with the original art.
>
> I have two different ways I work with the RAW file. Open in RPP 64 and create the lighting-lens-camera profile with RPP 64. I set RPP 64 for Kodachrome 64. Save the digital file as an RGB TIFF16-bit (BetaRGB). I had been saving the file as Lab TIFF 16-bit.
>
> LR 6 is next, and sizing is done in PS CS5.
>
> I do my best not to change what is digitally captured, in order to preserve the likeness of the original art.
>
> The other way I have my workflow, use LR 6. LR 6 will blend multiple RAW’s in RAW. Skip RPP 64 altogether.
>
> Comments are made that the x-rite CC is not the same as the pigments in the original art work. Therefore I wonder if this may be an issue?
>
> Those using Einsteins’, what size reflector is used?
>
> Many years back, someone in the museum industry, on this forum, told me to use the Schneider B+W UV-IR-CUT filter. Anyone remember who that was? Anyone also using the Schneider B+W UV-IR-CUT filter? Might have been in regards to cobalt blue.
>
> An NEC PA271w, and an NEC PA2721w are profiled with i1Pro and i1 Profiler. Two separate work stations. The Epson Pro 9900 is profiled for each different substrate, with i1 Profiler and read with the i1Pro.
>
> EOS 6D’s are my cameras.
>
> Questions?
>
> Kind Regards,
>
> David
>
>
> David B. Miller, Pharm. D.
> 3809 Alabama Street
> Bellingham, Washington, 98226-4585
> 360 739 2826,
>
>
>
> ------------------------------
>
> Message: 2
> Date: Fri, 18 Sep 2015 12:31:10 -0700
> From: "Millers' Photography L.L.C." <email@hidden>
> To: colorsync-users <email@hidden>,
> email@hidden
> Subject: Re: Colorsync-users Digest, Vol 12, Issue 114
> Message-ID: <email@hidden>
> Content-Type: text/plain; charset=utf-8
>
> Jon, please describe in detail your method written below…….(1/5 exposure) and cross polarized (4/5)
>
>> On Sep 18, 2015, at 12:00 PM, email@hidden wrote:
>>
>> In addition to the previously stated, my 4x5 fine art repro days included a blend of specular directional (1/5 exposure) and cross polarized (4/5). This captured better brush stroke textures.
>> Jon
>
>
>
> David B. Miller, Pharm. D.
> 3809 Alabama Street
> Bellingham, Washington, 98226-4585
> 360 739 2826
>
> ------------------------------
>
> Message: 3
> Date: Fri, 18 Sep 2015 12:50:33 -0700
> From: Ben Goren <email@hidden>
> To: colorsync-users <email@hidden>
> Subject: Re: Art Duplication
> Message-ID: <email@hidden>
> Content-Type: text/plain; charset="utf-8"
>
> On Sep 18, 2015, at 12:25 PM, Spinnaker Photo Imaging Center <email@hidden> wrote:
>
>> Workflow is camera white balanced with what is supposed to be a white target on one side, and black, gray, and white on the other side.
>
> While some white balance targets are more spectrally flat than others, nothing, not even Spectralon, is perfectly flat. Click-to-white-balance relies on a nonexistent physical property.
>
> If you know the camera's spectral response and the spectrum of the illuminant, you can predict the correct per-channel scaling factors for white balance without even taking a picture. If you photograph a sample with a known spectrum, you can compare the predicted and actual RGB values to automatically fine-tune the white balance. And if you have a number such samples -- such as with an entire ColorChecker -- you can average them for even greater precision. Of course, this same process will normalize exposure as well.
>
>> Comments are made that the x-rite CC is not the same as the pigments in the original art work. Therefore I wonder if this may be an issue?
>
> They're not exactly the same, but, then again, there's variation across manufacturing batches, changes with time and exposure to the elements, and so on. For typical photographic purposes, the differences can typically be ignored. For critical work, you'll want to use your own measurements of your own chart.
>
> The original 8x10 cardboard ColorChecker is superb when you want a large, physically thin and flat reference, especially for normalizing white balance and exposure. The ColorChecker Passport is, hands down, the best chart for field use as well as the best small chart for profiling. The extra couple dozen patches on the new half both give you as big a gamut with as saturated colors as you're reasonably going to get with such a device as well as an excellent sampling of the neutral axis. The integrated case gives it as much durability as you can reasonably expect. I've dragged mine all over the Desert Southwest....
>
> The two ColorCheckers serve different-but-overlapping purposes. If I could only have one, I'd easily go with the Passport. I have both and use both.
>
> I've made my own charts in the past. Were I continuing to use a profiling workflow based on reflective charts, I'd still use homebrew charts; you simply can't buy anything remotely in the same league as what you can make with a trip to the art store. But that workflow falls quite short of spectral modeling...and, as such, all I need charts for now are to fine-tune exposure and white balance. I can do that with a single patch better than you can with a click-to-white-balance, but it's just as easy to do it with an entire ColorChecker -- which gives negligibly fractional DE accuracy for colors near the neutral axis. Of course, the closer you get to the spectrum locus, other factors come into play....
>
> Cheers,
>
> b&
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> ------------------------------
>
> Message: 4
> Date: Fri, 18 Sep 2015 13:27:11 -0700
> From: Spinnaker Photo Imaging Center
> <email@hidden>
> To: Ben Goren <email@hidden>
> Cc: colorsync-users <email@hidden>
> Subject: Re: Art Duplication
> Message-ID: <email@hidden>
> Content-Type: text/plain; charset=utf-8
>
> Ben, for years you have written about home brew CC. I have never tried it since I would not know what color to purchase….oil, or watercolor, or pastels.
>
> I would not know how this home brew chart could be read. Or what to read it with.
>
> Cheers.
>
> David
>
>
>
>
>
>
> David B. Miller, Pharm. D.
> 3809 Alabama Street
> Bellingham, Washington, 98226-4585
> 360 739 2826
>
>
>
> ------------------------------
>
> Message: 5
> Date: Fri, 18 Sep 2015 14:17:31 -0700
> From: Ben Goren <email@hidden>
> To: colorsync-users List <email@hidden>
> Subject: Re: Art Duplication
> Message-ID: <email@hidden>
> Content-Type: text/plain; charset="windows-1252"
>
> On Sep 18, 2015, at 1:27 PM, Spinnaker Photo Imaging Center <email@hidden> wrote:
>
>> Ben, for years you have written about home brew CC. I have never tried it since I would not know what color to purchase….oil, or watercolor, or pastels.
>>
>> I would not know how this home brew chart could be read. Or what to read it with.
>
> If it's an actual 24-patch ColorChecker, unless you're going to be making it in volume, buy the real deal. If you'll be making them in volume, take your ColorChecker to the local home paint store (be sure it's a new one with an expanded gamut) and have them match the patches on their own color matching system; they'll mix up spectral matches for you using their own X-Rite branded hardware and software. If you plan on doing that for other than personal / internal use, run it by a lawyer; I've no clue what X-Rite's own lawyers might think if you started selling them. But, if you want to sell charts...the patch selection of the original ColorChecker is good but certainly can be improved upon; you'd be much better off making something original.
>
> If you want an high-patch-count chart with a large gamut and lots of interesting spectra, go to the local art store and buy lots of paints and some brushes and so on and paint a bunch of squares. Mix the paints in as many permutations of proportions as you've patience for -- and be sure to do multiple tints, especially of the darker colors, to bring up the chroma. Golden Fluid Acrylics is a good choice. Or, enlist the help of a local artist who's already got an extensive palette.
>
> In either case, you'll need to measure the patches with a spectrometer (such as an i1 Pro). For the homebrew chart, you'll also need to create the necessary chart recognition files for your profiling software. With Argyll, it's straightforward but the file format is very unforgiving; if it doesn't work right, it's because there's something not right in the files, and it may take some careful inspection to spot where you've gone worng.
>
> If you're going the homebrew route...don't think you have to make a single oversized chart with lots of teeny tiny patches to get a good patch count. A much better approach is multiple charts with large patches; combining the readings from multiple charts into a single input file for color profiling is trivial -- at least, it is with Argyll. Were I to do it again...I'd probably do 8" x 10" charts with ~1" patches = 80 patches / chart, and then make however many charts (each with a different selection of paints) as I felt inclined to make.
>
> If you're feeling extra inspired, you can make an overlay cutout like on the ColorChecker charts, either by hand with a razor or with a computerized paper cutter such as is popular amongst the scrapbooking crowd. Or you could start by putting down some masking tape to outline the patches, and discard the masking tape when done. Either method will make it much easier to get good clean straight edges to help the edge detection algorithms identify the chart's location and orientation. But, even if not, you can digitally overlay a similar mask in Photoshop or Affinity Photo or the like before feeding the picture to the profiling engine.
>
> But...again, chart-based profiling is suboptimal in many ways, and not at all what I do today....
>
> Cheers,
>
> b&
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> ------------------------------
>
> Message: 6
> Date: Fri, 18 Sep 2015 14:26:17 -0700
> From: Robin Myers <email@hidden>
> To: "'colorsync-users?lists.apple.com' List"
> <email@hidden>
> Subject: Re: Art Duplication
> Message-ID: <email@hidden>
> Content-Type: text/plain; charset=windows-1252
>
> Dr. Miller:
>
>> <snipped>
>> I might just see where some of my issues come in. Could it be the cardboard x-rite CC? (I refuse to use the passport CC).
>
> The ColorChecker Passport uses the same patches on its ColorChecker Classic page as the cardboard ColorChecker Classic so there is no reason not to use the ColorChecker Passport. There are added benefits on the facing Photo Enhancement page with finer spaced dark grays and light grays and the higher saturated spectrum colors. These extra patches can be used to evaluate your images and profiles. More information on the ColorChecker Passport may be found at http://rmimaging.com/information/ColorChecker_Passport_Technical_Report.pdf.
>
>>
>> Workflow is camera white balanced with what is supposed to be a white target on one side, and black, gray, and white on the other side. These three shades are for me to determine, exposure. Then, I use the white only side to determine white balance in camera.
>
> This is one source of your color error. If you examine the spectra of the white patch on this chart you will find that it is not white but very pale yellow. The color is specified as Munsell N9.5 and an average of 12 ColorCheckers of various ages produces L*a*b* values of L* 96.4, a* -1.0, b* 3.1. We perceive the color as white because it is the whitest object in our field of view and the human vision system adapts to make it appear white. Because the white patch is not white, the white patch should be used for setting the exposure only.
>
> Instead, you should set the neutral balance, white balance is a misnomer, with the gray patch on this chart. The gray patch is specified as Munsell N5 which I have measured and averaged from 12 ColorCheckers as L* 50.9, -0.4, 0.1. This is definitely more neutral than the white patch and a better choice for neutral balancing. It is also light enough to produce a good signal-to-noise ratio in the camera’s sensor.
>
> The black patch is specified as Munsell N2 and should be used to check for veiling glare. Veiling glare can be controlled by using a lens hood and surrounding the subject with a black background.
>
> <snipped>
>
> Mr. Goren:
>
>> <snipped>
>>> Workflow is camera white balanced with what is supposed to be a white target on one side, and black, gray, and white on the other side.
>>
>> While some white balance targets are more spectrally flat than others, nothing, not even Spectralon, is perfectly flat. Click-to-white-balance relies on a nonexistent physical property.
>
> While PTFE references such as Spectralon® and Fluorilon® do not exhibit perfectly flat spectral reflectances, they are the best materials presently available for white reflectance standards and are used as such for calibrating spectrometers by many companies and NIST. PTFE is the only white material I recommend for neutral balancing cameras. The majority of white objects, including the white patch on ColorChecker charts, use a titanium white pigment which is actually a pale yellow, as noted above. If these white objects are used for neutral balancing a camera the resulting images will have a slight blue color cast.
>
> Robin Myers
>
>
>
> ------------------------------
>
> Message: 7
> Date: Fri, 18 Sep 2015 15:11:14 -0700
> From: Ben Goren <email@hidden>
> To: "'colorsync-users?lists.apple.com' List"
> <email@hidden>
> Subject: Re: Art Duplication
> Message-ID: <email@hidden>
> Content-Type: text/plain; charset="iso-8859-1"
>
> On Sep 18, 2015, at 2:26 PM, Robin Myers <email@hidden> wrote:
>
>> While PTFE references such as Spectralon® and Fluorilon® do not exhibit perfectly flat spectral reflectances, they are the best materials presently available for white reflectance standards and are used as such for calibrating spectrometers by many companies and NIST.
>
> PTFE makes for a great reference standard, but, best I know, outside of photographic click-to-balance workflows, it is not used in a manner that assumes that it is pure white.
>
> If you measure the calibration tile included with an i1 Pro -- the one that you have to put the instrument on before every session -- you'll see that it's decidedly less white than PTFE. It's got a curved spectral reflectivity significantly less than 100%. But it's a beautifully smooth spectrum, and presumably the material is very stable. It's plenty reflective enough that it presents an high signal-to-noise ratio for the electronics. PTFE is also stable and has an even higher reflectivity, making for marginally better absolute properties. But it's less durable than the ceramic used for the i1, and I'm sure much more expensive, which would explain why X-Rite used the ceramic instead.
>
> You don't need an absolute white reference for spectrometry. The instrument (or software) knows what the combined reflected spectrum of its lamp and reference is supposed to be; whatever it measures at the time of calibration is used to create an offset to correct for whatever momentary conditions from the environment or whatever are causing drift. You could use a lump of coal or a colored ink or whatever for that, save the readings would get noisy.
>
> <blockquote>PTFE is the only white material I recommend for neutral balancing cameras.</blockquote>
>
> If you're doing the click-to-balance method, PTFE is as good as it gets. Thread seal tape (like what plumbers use) is a good, cheap source; layer it up to ensure opacity. BabelColor used to sell an affordable 1" circular Spectralon (or equivalent) target, but that was years ago. Actual Spectralon targets are available for insane prices.
>
> But...there're two cheap alternatives that every photographer should be aware of.
>
> First is Tyvek. It's nearly as good as PTFE, and you can buy it cheap, usually in the form of envelopes, at your local office supply store. It's nearly indestructible, which is why it's used for envelopes. It's got a bit of specularity to it, including grain in the specularity, so you have to be careful with lighting. At the same time, if it throws no specular highlights, neither will whatever you photograph.
>
> Second...is styrofoam. I'm not aware of any commercially-available white balance target other than Spectralon that's as good as a styrofoam coffee cup. As a bonus, the conical shape lets you get directional samples in mixed lighting. Or a styrofoam sphere from a crafts store could do the same.
>
> Again again, best is to predict the RGB values for the scene's combination of the camera's spectral response plus the illuminant's spectra and the spectral reflectivity of a number of patches. Click-to-balance is a shortcut for an unique class of circumstances that doesn't actually exist, though there're a number of easy-to-attain not-entirely unreasonable set of approximations that are "good enough" for non-critical work.
>
> Cheers,
>
> b&
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> ------------------------------
>
> Message: 8
> Date: Fri, 18 Sep 2015 15:47:58 -0700
> From: Spinnaker Photo Imaging Center
> <email@hidden>
> To: Ben Goren <email@hidden>
> Cc: colorsync-users List <email@hidden>
> Subject: Re: Art Duplication
> Message-ID: <email@hidden>
> Content-Type: text/plain; charset=windows-1252
>
> Thank you Ben.
>
> Chart would be only for my personal use……..Now, if I missed it, what do you do today?
>
>
>> On Sep 18, 2015, at 2:17 PM, Ben Goren <email@hidden> wrote:
>>
>> what I do today....
>
>
>
> David B. Miller, Pharm. D.
> 3809 Alabama Street
> Bellingham, Washington, 98226-4585
> 360 739 2826
>
> ------------------------------
>
> Message: 9
> Date: Fri, 18 Sep 2015 16:35:40 -0700
> From: Ben Goren <email@hidden>
> To: colorsync-users List <email@hidden>
> Subject: Re: Art Duplication
> Message-ID: <email@hidden>
> Content-Type: text/plain; charset="windows-1252"
>
> On Sep 18, 2015, at 3:47 PM, Spinnaker Photo Imaging Center <email@hidden> wrote:
>
>> Thank you Ben.
>>
>> Chart would be only for my personal use……..Now, if I missed it, what do you do today?
>
> Short version...I take a picture of a diffuse light source viewed through a spectroscope and extract RGB values from it. That plus an i1 Pro measurement of the light source and separate measurements of the transmission efficiencies of the diffraction grating and the lens gets me the camera's per-channel spectral sensitivities. Once you've got that, you can combine it with the spectrum of any illuminant and the efficiency of any lens / filter combination to predict RGB values for any known reflective spectrum. And I do so for tens of thousands of virtual samples to create a virtual chart with that many patches and use Argyll to build a profile from that. It's specific to the illuminant and lens, but then so is any profile.
>
> I'll be doing a full writeup in the hopefully-not-too-distant future....
>
> Cheers,
>
> b&
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