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Author Topic: HR-1 SuperChroma  (Read 6266 times)

Jim Kasson

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Re: HR-1 SuperChroma
« Reply #40 on: May 17, 2020, 04:39:53 pm »

ok, good to know the Soraa lights can be ruled out. Any experience with Waveform? They have a claimed 99CRI D65 LED strip source that I could use to build a lamp.

https://store.waveformlighting.com/collections/led-linear-modules/products/absolute-series-99-cri-led-linear-module?variant=8190565777510

Thanks for the pointer to Solux, and to Godox for bulbs. I will need to take some photos of actual products at some point - won't only be able to use the spectrophotometer directly on paint sample panels. That said - for sample panels - if I were to buy an off the shelf solution rather than build a box, is Just Normlicht clearly better/worse than Pantone?

The Godox are strobes, not bulbs. I'd use those instead of LEDs, and I'd use standard light modifiers. I wouldn't put too much credence in CRI for this kind of work; it's only using 18 patches of the CC24.

Why won't you be able to use a spectro directly on the sample panels?

As to the sample images, you could just use a Lumariver Repro profile, and edit the pictures so that the painted parts fell into the range indicated by your spectro measurements.

Jim
« Last Edit: May 17, 2020, 04:43:08 pm by Jim Kasson »
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Jim Kasson

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Re: HR-1 SuperChroma
« Reply #41 on: May 17, 2020, 04:45:00 pm »

ok, good to know the Soraa lights can be ruled out. Any experience with Waveform? They have a claimed 99CRI D65 LED strip source that I could use to build a lamp.

https://store.waveformlighting.com/collections/led-linear-modules/products/absolute-series-99-cri-led-linear-module?variant=8190565777510

These still have spikes in the blue part of the spectrum.

sea-speak

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Re: HR-1 SuperChroma
« Reply #42 on: May 17, 2020, 05:26:41 pm »

Got it. Understood that the Godox are strobes. I typed 'bulb' when I should have typed 'flash tube'. I meant that I understood you to be telling me that the Godox flash tubes are reasonably good.

And, sorry, I got myself a little confused there - thought I would need to have a D65 light source separate from the spectrophotometer for characterizing paint samples, but of course the spectrophotometer has that source built into it. (And, having spent enough time on the Solux website I now see that they offer the Colorview 6500K light booth, which should be adequate should I need to use my camera to photograph paint samples; I can imagine scenarios in which that becomes useful)

So putting this all together:

1 - making web rendering colors as accurate as possible (I am using Keyshot for CAD rendering, will have Keyshot interactives on the website, and will have to figure out how to set the sRGB values in that software for a given color):
-Produce paint samples with the actual paint on the actual substrate
-Measure physical samples w i1 spectrophotometer and convert to sRGB coordinates for web display purposes
-Use Babelcolor patch tool to manage the sample collection and conversion process
-Calibrate monitor with the same spectrophotometer, and suggest less expensive version (e.g. i1 Display Pro) to customers if they are interested in picking a custom color (to make the narrowing-down process more efficient).

2 - When making photos of finished product:
-Use good quality strobes (e.g. Godox). Sounds like if I can generate the environmental illumination with Solux bulbs that would be ideal.
-Use ColorChecker SG target (or other wide-gamut target that uses spot rather than process colors).
-Monitor calibration, etc. as above.

Have I correctly understood the basic workflow elements?

 
« Last Edit: May 17, 2020, 11:01:16 pm by sea-speak »
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digitaldog

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Re: HR-1 SuperChroma
« Reply #43 on: May 17, 2020, 06:00:16 pm »

As for CRI, it's a bit of a kludge to make a light source appear to be closer to daylight for marketing and light manufacturers. CRI was developed in large part to aid in the sales of Fluorescent tubes. There are BCRA tiles used to compare under a reference light source but only eight. That's too small a set of tiles. That make it easy to create a spectrum that will render the 8-14 tiles and doesn't tell us that the light source is full spectrum. It doesn't tell us how the other colors will render. My understanding is there are two reference sources; Tungsten for warm bulbs and D50 for cool ones: Above and below 4000K. That means that a normal tungsten bulb and perfect daylight both have a CRI of 100! As such, a high CRI is a decent gauge of how well a light will preform in your home but not such a great indicator of how well it will work for photography and proofing. Both a Solux 48 and a "full spectrum" tube from home depot may have a CRI of 97. I can assure you the Home Depot bulb has a giant mercury spike and some spectral dead spots. 

A better metric is called CQS (15 very colorful patches). That doesn't tell us about the spectrum which is even a better way to evaluate the illuminant. 
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hurodal

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Re: HR-1 SuperChroma
« Reply #44 on: June 03, 2020, 06:09:39 pm »

Hugo, what is your preferred hardware & software workflow to utilize your card?

thanks --

Brandt

Regarding to hardware, well, that's up to your taste and budget. Almost any decent camera these days with a good lens cap be up to the task. However, regarding to color gamut of the sensor, Canon and Sony not high res are some of the best.
In terms of profiling software, I've found that the best are BasICColor Input and Profilemaker 5 (yes, still the old one) followed (by a noticeable margin) by Lumariver and all Argyll-based software.
For RAW developing: CaptureOne without any doubt.

PS: Thanks for the empathy.
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Hugo Rodriguez

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digitaldog

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Re: HR-1 SuperChroma
« Reply #45 on: June 03, 2020, 07:09:01 pm »

However, regarding to color gamut of the sensor, Canon and Sony not high res are some of the best.
And yet, neither has a color gamut. Cameras don't have color gamuts. An arbitrary colorimetric camera profile may have a color gamut but the camera doesn't. 
http://www.color-image.com/2012/08/a-digital-camera-does-not-have-a-color-gamut/
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Jim Kasson

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Re: HR-1 SuperChroma
« Reply #46 on: June 03, 2020, 11:38:53 pm »

Regarding to hardware, well, that's up to your taste and budget. Almost any decent camera these days with a good lens cap be up to the task. However, regarding to color gamut of the sensor, Canon and Sony not high res are some of the best.

I've found that a good lens cap makes capturing good colors difficult. A lousy lens cap works better. Or even no cap at all.

I'm with Andrew on the gamut of sensors, except in special cases not found in real cameras.

Jim

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Re: HR-1 SuperChroma
« Reply #47 on: June 09, 2020, 03:52:38 am »

Sensors have a color gamut because its limited by the very filters of the CFA.
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Hugo Rodriguez

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Re: HR-1 SuperChroma
« Reply #48 on: June 09, 2020, 09:55:42 am »

Sensors have a color gamut because its limited by the very filters of the CFA.
Sorry, completely wrong. Ask some actual color scientist!
I did! I asked it to Mark D. Fairchild from RIT and I just would like to share his answer here:

"This one is easy for me … cameras absolutely do not have gamuts
A color gamut is the range of colors produced by a device or system. I can take an image from any camera and produce any colors I like. 

So I fall strongly, and unequivocally, on the side that says cameras do not have color gamuts. (FWIW, this isn’t even a discussion among the faculty in our program, we all agree on this.)
The human eye also does not have a gamut. The spectral locus on chromaticity diagram (which is also missing a dimension) simply shows the response of the eye to monochromatic light. The limit is in the light, not the eye. The camera can also respond to all that light."
« Last Edit: June 09, 2020, 10:14:31 am by digitaldog »
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ErikKaffehr

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Re: HR-1 SuperChroma
« Reply #49 on: June 11, 2020, 02:04:42 pm »

The chart is printed with Epson Ultrachrome inks.
Regarding the spectral characteristics, though there are not present the exact same colors as -say- the ones in the Colorchecker in the Superchroma, there are some patches that are very similar both in color and spectral curve. I can send you graphs in you wish.
Regards,

Hi,

I am not sure inkjet prints are very good for calibration targets. The reason that the colors are just a mix of inkjet inks that are intended to yield a metameric match for the the colors printed under a set of viewing conditions.

My guess would be that if you look at say a reflectance spectrum from say 'human skin' and compare with reflectance spectrum from a printed patch, they could have very different spectral response, they could still yield Lab values that are pretty.

So, I would avoid printed targets, but use some well established test chart, like the ColorChecker variants from XRite.

Best regards
Erik
 
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digitaldog

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Re: HR-1 SuperChroma
« Reply #50 on: June 11, 2020, 02:15:32 pm »

I am not sure inkjet prints are very good for calibration targets.
Neither is Jim or I. But the one fellow who is sure digital cameras have a color gamut (despite the text from no less than three color scientists who say they do not) is sure it's an OK process. But then there's a sales incentive here no?  :o
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ErikKaffehr

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This may be interesting...
« Reply #51 on: June 18, 2020, 08:22:29 am »

Neither is Jim or I. But the one fellow who is sure digital cameras have a color gamut (despite the text from no less than three color scientists who say they do not) is sure it's an OK process. But then there's a sales incentive here no?  :o
Not a gamut:


'This diagram in u’v’ chromaticity coordinates shows the color separation capability of a Canon EOS 5D Mark II.'

Black areas essentially indicate areas where the sensor is 'color blind', that is cannot separate between colors. The irregular shape is "Pointer's gamut" that includes all known non specular colors in nature.

Source: https://torger.se/anders/dcamprof.html

Best regards
Erik
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digitaldog

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Re: HR-1 SuperChroma
« Reply #52 on: June 18, 2020, 12:02:11 pm »

From the FAQ's on Munsell Color Science Laboratory:

Question:
"Digital image sensors (such as those used in digital cameras) use red, green, blue ink-based color filters to generate color. Do they therefore have a color gamut that limits the range of colors that they can detect? (255)"

Answer:
"Let's start with the short answer to your question; there is no such thing as a camera, or scanner, gamut. A gamut is defined as the range of colors that a given imaging device can display. To say that a camera had a gamut would be to imply that you could put a color in front of it that it could not possibly respond to. While it is certainly possible that two colors that are visually distinct might be mapped into the same color signals by a camera, that does not mean that the camera could not detect those colors. It just couldn't discriminate them. For example, a monochrome sensor will map all colors into a grayscale image and encode it as such. Certainly the encoding has a gamut (in this case a lightness range with no chroma information), but did the camera responded to all the colors put before it. It is the encoding that imposed the gamut. In the color world, encoding is based on some explicit or implied display. For example, sRGB is a description of a display and therefore defines a gamut (but only if the sRGB values are limited in range). If a camera encodes an image in sRGB, that doesn't mean that the range of colors the camera detected are only from within the sRGB display gamut, but it means the camera data have been transformed to best use that sRGB encoding. As long as a camera has three or more sensors that span the visual spectrum, then it will respond all the same stimuli as our visual system. Whether the camera can discriminate colors as well as the human visual system will depend on the encoding of the camera signals, quantitization, and the details of the camera responsivities. (To return to the black and white system, that camera encodes all the colors into a gray scale. They could then be displayed as any color within a given display, but many colors from the original scene would be mapped to the same values.)

Since there is no such thing as a gamut for an input device, then there is no way to compute it or calculate a figure of merit. Generally, the accuracy of color capture devices is assessed through the accuracy of the output values for known inputs in terms of color differences. Also, sensors are sometimes evaluate in terms of their ability to mimic human visual responses (and therefore be accurate) using quantities with names like colorimetric quality factor, that measure how close the camera responsivities are to linear transformations of the human color matching functions. Doing an internet search on "colorimetric quality factor" will lead you in the right direction."

https://www.rit.edu/cos/colorscience/rc_faq_all.php#255

I'll post this again too:
Digital cameras don't have a gamut, but rather a color mixing function. Basically, a color mixing function is a mathematical representation of a measured color as a function of the three standard monochromatic RGB primaries needed to duplicate a monochromatic observed color at its measured wavelength. Cameras don’t have primaries, they have spectral sensitivities, and the difference is important because a camera can capture all sorts of different primaries. Two different primaries may be captured as the same values by a camera, and the same primary may be captured as two different values by a camera (if the spectral power distributions of the primaries are different). A camera has colors it can capture and encode as unique values compared to others, that are imaginary (not visible) to us. There are colors we can see, but the camera can't capture that are imaginary to it. Most of the colors the camera can "see" we can see as well. Yet some cameras can “see colors“ outside the spectral locus however every attempt is usually made to filter those out. Most important is the fact that cameras “see colors“ inside the spectral locus differently than humans. I know of no shipping camera that meets the Luther-Ives condition. This means that cameras exhibit significant observer metameric failure compared to humans. The camera color space differs from a more common working color space in that it does not have a unique one to one transform to and from CIE XYZ. This is because the camera has different color filters than the human eye, and thus "sees" colors differently. Any translation from camera color space to CIE XYZ space is therefore an approximation.

The point is that if you think of camera primaries you can come to many incorrect conclusions because cameras capture spectrally. On the other hand, displays create colors using primaries. Primaries are defined colorimetrically so any color space defined using primaries is colorimetric. Native (raw) camera color spaces are almost never colorimetric, and therefore cannot be defined using primaries. Therefore, the measured pixel values don't even produce a gamut until they're mapped into a particular RGB space. Before then, *all* colors are (by definition) possible.

Raw image data is in some native camera color space, but it is not a colorimetric color space, and has no single “correct” relationship to colorimetry. The same thing could be said about a color film negative.
Someone has to make a choice of how to convert values in non-colorimetric color spaces to colorimetric ones. There are better and worse choices, but no single correct conversion (unless the “scene” you are photographing has only three independent colorants, like when we scan film).
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