ankorwatt said:
you have many remarkable statements , and what do you know about the color fields in qp-card and how they are produced?
http://www.qpcard.com/en_b2c/colors-on-card .
http://www.qpcard.com/en_b2c/dcp_icc_profile In
reality Profoto handle all colors and nuances except some cyans in mathematic model and who have no interest .
What do I know about color? Not much, granted -- especially in comparison with true digital color scientists such as Graeme Gill and Bruce Lindbloom. But I know a hell of a lot more than whoever wrote that page you link to, which has real doozies like this on it:
Manual white balancing, using a neutral gray target in the scene, is the best way to achieve neutral grays in the picture. However, it doesn't matter if the gray target is manufactured by Kodak, Datacolor, X-rite or QPcard; the end result is the same.
First, using a chart with a single gray patch on it to achieve gray balance is, by definition, the worst possible empirical method for the task. A chart with two gray patches is much superior, and a full-sized color chart is ideal.
Second, the notion that the manufacturer doesn't matter and that all produce the same results is ludicrous. If you
are going to use the click method, the uniformity of the spectral reflectivity of the target is paramount, and none of the targets on the market are as spectrally uniform as even a styrofoam coffee cup. (Well, with one notable exception: anything from LabSphere made of Spectralon. But those targets cost as much as an L lens.) I know -- I've got many of them and I've measured many of the rest with a spectrophotometer. I've actually got a can of paint from Home Depot that's much better than average, thanks to a helpful response to a query I made to their technical support group.
Anyway, that's just the easy and trivially obvious misinformation on that page. They also suffer from misconceptions such as this:
The color samples are divided into four groups. The primary groups have 9 saturated samples of red, green and blue picked to accurately determine the spectral midpoints of the on-sensor filters.
It's a nice-sounding idea, but completely worthless. Neither ICC nor DNG profiles give a damn what the spectral midpoints of the filters are. If you had a complete map of the complete spectral sensitivity of each filter, you could probably generate a model of the camera's response well enough to create not-bad profiles from that information...but you'd need not just the spectral midpoint but enough other points on the curve to plot the entire thing. The green-filtered photosites
are sensitive to red and to blue light, but not very sensitive. Knowing how sensitive they actually are would be essential to the type of modeling they're trying to make you think they're performing (and that perhaps they themselves even think they're performing), but you're not going to get that in any useful form from photographing the chart they're selling.
At best, they're well-intentioned but not very clueful. Maybe they're trying to reinvent the wheel without bothering with learning the fundamentals. Or maybe whoever is writing their marketing materials is clueless. Or maybe they're just blowing smoke up everybody's asses with technical-sounding bafflegab and a run-of-the-mill product.
Regardless, you've fell for their hype, hook, line, and sinker.
Considering that your knowledge of color science is so limited that you aren't aware of all the quantization and color shift and other problems associated with ProPhoto, it's not surprising that you'd be taken in by that kind of salesmanship. Color science is a deep and obscure field, and it's easy to get confused, which makes it even easier for people to intentionally or unknowingly confuse others, including for personal monetary gain.
But QPcard truly is, at best, a run-of-the-mill product. That the hype surrounding it makes it seem like the greatest thing since sliced bred when it truly isn't is enough reason to not give them any financial support by buying their products, even if they're truly sincere about the hype.
If you want a better color target than any you can buy today, it's not hard. Start with a classic ColorChecker; take it to your local paint store and have them match each of the colors. You might need to go to the newest paint store in town, as some of the colors are too saturated for those with older formulations to match. But the matches will be good spectral matches within the observed variation of the official targets over the years.
Next, go to your local art store and get a sample sheet / book / whatever of artist's paints. Golden Fluid Acrylics works well for this purpose, but they're hardly the only ones. Measure the samples with your spectrophotometer and pick a dozen or so samples with a representative mix of spectra. Buy those paints as well as a bit of white.
Now lay out your chart in Photoshop. You'll want the ColorChecker somewhere in the middle. You'll want each of your artist's paints in a few shades (mixed with white). You'll also want a number of patches that you'll print, including a dozen or so neutral patches as well as at least a hundred, preferably twice or more, patches distributed uniformly throughout perceptual space -- and, obviously, you'll need to have a good profile of the printer and paper you'll be using to generate that patch set. For bonus points, include a bit of PTFE thread tape for your whitest patch, a black trap (make the target a hollow black-lined box with a patch-sized hole for your darkest patch), and samples of real-world objects you'll care about (such as wood chips).
Print the target, paint in all the paints you've assembled, let it dry a day or three, measure the patches with your spectrophotometer, and build your profiles.
If your paint store will sell you pint-sized samples and if you're friendly with an artist who'll let you use her paints, you can build for yourself a color chart that puts everything on the market to shame for not much more than that QPcard will cost you...plus, of course, a significant investment in your own time....
Cheers,
b&
