I know what black is. It is the total absence of color. When you look at something black, like the letters on this post, you’re not seeing the black. You’re really seeing nothing, which your brain registers as black.
I think I know what white is. When the item in question reflects back all colors, you perceive it as white. In French they call white blanche. Blanche is ultimately where we get our word ‘blank’ from, which makes a lot of sense. White holds no colors, so in a sense it really is blank. No?
So what is gray then? I know it’s black and white mixed together. But that doesn’t make any sense. As I just explained, black and white are opposites. So how could they mix together?
I think it’s white with some type of black filter over it. Whether that be a mesh screen, smoke particles, black dots from a printer, etc.
White snow turns to gray when black dirt particles appear in it.
I think you need to read up on the subjects of lightness and luminance. Luminance is a measure of how much light is coming off an object, and lightness is a measure of how humans perceive luminance.
That’s a bit harsh. I mean, from the basic physical principles involved one might predict that if something partially absorbs and partially reflects (at all wavelengths) it would still look white, but be less bright. What is the difference between something white but dimly-illuminated and something that is gray? Perhaps the only difference is in how our brains interpret relative brightness in context, but it does not seem like a completely trivial question to me.
Not all whites are created equal. Or so I’ve heard.
Black can only be so black: when zero photons are hitting your retina, that’s as black as it gets. But for any “white” image you can look at, I can show you one that’s even brighter, i.e. more photons per second are hitting your retina. The white image I show you becomes your new white reference, and what you previously thought was a white image is now understood to be just a bright gray.
And then I can show you another image that’s even whiter. Now you’ve got a newer, brighter white reference, and your catalog has two different shades of grey in it instead of one.
At some point the sensors in your retina will of course be saturated, and you will be perceiving the whitest white you possibly can. If you want to appreciate a wider range of white, you’ll need to use a filter to block some of the photons so that you don’t roast your retina; this is a little bit like using a voltage divider so that a volt meter that’s only capable of measuring up to 5 volts can be used to measure a car battery. Alternatively, you could use an artificial light sensor that’s capable of measuring much brighter whites than your eyeball can.
TL,DR: What’s gray? It’s a photon flux that’s somewhere between zero and the highest value your sensor is capable of measuring.
In terms of what photons interact with your eyes, there is nothing different, they are potentially identical. In terms of how the differently colored surfaces interact with the world around us, the white surface will reflect more of the ambient light than the gray surface. Our brains can interpret those factors and tell us one is white and the other gray, even if their scattered photons are identical. We can predict what will happen if the light changes, or if the surface changes position.
Right. Which supports the idea that it’s actually a very interesting question. You could argue that in fact we do only have black, white, and how our brains interpret them in context.
It’s a puzzle. The reflected light that impinges in our eyes is interpreted by our brains in ways we do not really understand. It is certain that what our brain sees is heavily influenced by our previous experiences.
When you see a colour you only know what it is because you learned it somewhere. What you think of as grey may be a tint of a different colour There have been many examples on the interweb.
The greyscale - white, black, and everything in between - do not exist as a specific frequency on the light spectrum. These ‘colors’ are optical illusions produced when the three types of cone cells (short = most sensitive to blue light, medium = green light, long = red light) in your eyes are equally excited.
A lot of this is theory talk. It applies to light mostly. If you open a can of black paint and peer inside, you are not seeing nothing. You are seeing what we call black.
Further if you mix all the colors of paint together it will NOT be remotely close to white, it will be a muddy grey brown.
My dad used to be fond of saying wheels don’t roll - segments of the surface take turns touching the ground. Yes, but that’s the definition of rolling.
A definition of grey can be equal amounts of black medium and white medium mixed together.
No, it is not solely cone activation. A gray monitor patch does not stimulate your S cones nearly as much as they have different sensitivities besides peak wavelength. Using my monitor in not very controlled situations, I get equal cone = RGB (49, 181, 255), sort of a light blue.
For OP: it does depend on if you are measuring “gray” light or a gray object. In the former you have to account for both the spectral power distribution of the light but also human vision. It sounds like you’re doing the latter in which case you also need the spectral power of the light source, whether it’s the sun or the lightbulb. If you don’t have that info or don’t want to assume environment, you can choose from a variety of standardized light sources.
Which is why color printers have 4 cartridges/inks and not 3. Cyan, magenta, and yellow can provide a decent range of reproducible colors, but not for very dark colors where blacK (the K in CMYK) comes in.
If you want a paint to be gray, you add a tiny bit of black and then another tiny bit and another to your white until you get the shade you want. Mix equal parts and you’ll get something that is a lot more like black than white.
Mixing paint and mixing light are completely different.
If you take a card that you think looks black and shine a bright enough light on it, it will look white. There are optical illusions based on our perception of black white and gray based on how much light it can reflect vs. how much light is being dumped on it.
Similarly, the screen used in cinemas is white and yet, somehow, you can perceive black projected upon it. Or rather the absence of light on a white screen is perceived as black.
No, at least not when you’re talking about light. White light has ALL the colors in it, and you can separate them out with a prism. Tinted light is missing some colors, and black is the absence of all light. White is RGB 255, 255, 255 and black is 0, 0, 0 while a medium gray is 128, 128, 128. Pigments are effectively the opposite. You start with a white base and add colors to it, approaching black. It’s not QUITE so simple in practice, but that’s a good way to approach it, and of course our perception of color and brightness has everything to do with light and not the pigments reflecting the light. So that white paint that has no pigment is reflecting white light from a light source, and if that light source doesn’t have all colors in it then the paint won’t look white, etc.
