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I've been trying different pencils, crayons, acrylic and watercolor paint, oil pastels, but I haven't been able to find anything that I can take picture of, and invert/negate digitally to make a bright red color.

At best I am able to get orange with "sky blue" ish colors, and magentas with some teals but nothing seems to produce a primary red(hue 0 in hsv, preferably with 75+ saturation, 75+ brightness).

Here is a picture of my screen with a cyan rectangle on it, which succeeds inverting to red, although a bit dark. In the process of taking the picture, it shifted to hue 173, saturation 54, brightness 100 from the original hue 180, saturation 100, brightness 100. but this is largely if not completely due to a bad camera, the computer screen cyan seems like the brightest cyan I've ever seen other than perhaps cuba ocean, and I might be misremembering about that(it might just be bright aqua).

maybe there's cyan somewhere here?

lots of oranges and red violets but few(any?) true reds

Here's a cropped google result similar to what I remember of cuba, but even so it has no perfect red at all indicating absence of very bright true cyan, but again it might be because of image capturing process, and there still might be some grayer cyans that I haven't been able to filter out.

Is there any reason why sky blue(eg hue 191, 80, 100) is the closest I can get to true cyan using non direct light emitting media?

I am just a bit confused since cyan blue is incredibly easy to invert into since yellow is quite abundant, and green is incredibly easy to invert into since red-violets are quite abundant, but red seems really tricky, even after buying sets of 100 pencils, 96 crayons, various paint sets, none of them have any colors that invert into red, at best, only teal and sky blue come close but don't invert to red.

Sidenote, I have managed to find that a few teals could invert into hue 2, saturation 74, brightness 68, which is really close, but is too dark of a color to work as a subtractive primary.

I imagine there must be butterflies that can force this wavelength to be reflected with nanostructures.

Is there no pigment that blocks only red wavelength, why is true cyan so rare or nonexistent?

What's stranger is that inverted space has plenty of bright cyans yellows and magentas, and non inverted space has plenty of reds, greens, and blues, but inverted space reds are really rare, and regular space cyans are really rare.

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    Excuse me, but why do you try to find materials for taking a picture to get some wanted color by inverting or otherwise processing the photo? As far as I know, the camera produces only three numbers (r, g and b) and thats all what's left , no other information of the material and light isn't stored. I cannot understand why you do not start directly from the wanted rgb numbers or their 100% equivalent hsv or hsl numbers. – user287001 Aug 3 '18 at 7:21
  • i am not sure i understand your question. I am aware i can start digitally to begin with or color correct the photo as i want, i am curious whether true cyan paint/pencil/or similar exists or if phthalo blue is the best we can get. And whether there is any inherent limitation to having true cyan if it doesn't exist outside light emission/shadows of light emission. – Dmitry Aug 3 '18 at 7:26
  • OK, you are interested in the properties of materials, you're not trying to produce numbers in a computer color system, you are trying to get materials which will in a camera produce certain color numbers. Understood. – user287001 Aug 3 '18 at 7:31
  • @Dmitry pure pigments that ere not going to kill you are hard to achieve. – joojaa Aug 3 '18 at 8:11
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    I agree with Yorik. Even if you find a truly cyan crayon, you might not be able to photograph it. Have a look at this comparison between RGB profiles gamut. The cyan part of the spectrum seems to be lacking in all RGB profiles. And even if your camera uses something better than sRGB, it might not be able to actually photograph every color which lies within the gamut of its color profile. – Wolff Aug 3 '18 at 15:19
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Colors on a monitor will always be more vibrant than anything that relies on a filter reflection. Off course you can get brighter self emitting colors, but those are extremely poisonous. You can get more intensity with paints as opposed to crayons.

Butterflies dont use pigments they use diffraction structures. So far we do not know how to lay these out by pen or paint. We only know very expensive manufacturing methods (as in one page would cost in excess of 10,000$).

What you need to do is use a trick make the image really muted in color palette. See human eyes are not sensitive to color per see. But color in relation to other colors. So if you make the image much more muted grayish suddenly even very dark and muted colors look more bright.

  • i wouldn't say always, monitors really struggle with bright pinks. I am aware that i can keep all my colors fairly muted, and increase saturation and brightness manually, but that bypasses the question of whether even a red at lower saturation/brightness absorbing material that doesn't absorb any green nor blue at all exists (hue 0). – Dmitry Aug 3 '18 at 8:20
  • @Dmitry - no that's incorrect, monitors have a much wider colour gamut than any physical pigments. For example, this is why CMYK printing cannot reproduce many RGB colours. – Billy Kerr Aug 3 '18 at 8:25
  • *continued I am aware that i can keep all my colors fairly muted, and increase saturation and brightness manually, but that bypasses the question of whether even a red at lower saturation/brightness absorbing material that doesn't absorb any green nor blue at all exists (hue 0). I also noticed the contrast trick, even a black border helps, and gradients can be used as well, but that doesn't really answer my question. here's one video regarding the pink but even less intense prismacolor pencil pinks seem impossible to color pick youtu.be/_NzVmtbPOrM – Dmitry Aug 3 '18 at 8:31
  • cmyk is different because it involves printing using a limited color spectrum, it only covers a partial color space, i am not arguing that screen will always be more vibrant than printer output (unless it's a particularly special printer) – Dmitry Aug 3 '18 at 8:34
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    @Dmitry Does not matter you can not get much purer colors. Same problem. – joojaa Aug 3 '18 at 8:43

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