True color reproduction by science

You are talking to us today about color photography. It’s not really a hot topic, is it?

Therefore, I will not tell you about color pictures or pictures. This, in fact, we have been doing for more than a century. No, I’m going to talk to you about color photography, which we still don’t do.

what do you want to say ?

Well, in nature, there are an infinite number of colours, and we are able to distinguish about 2 million of them. On the other hand, all the devices that we use to record or reproduce colors distinguish only 3 of them, for example monitors generate blue, red and green only. And it’s the same for printers, we just put three different colored inks, yellow, cyan, and magenta.

Yes, but with three colors, we can recreate all the others

Not exactly. With 3 colors, we only have 3 colors, and we only send 3 colors into our eyes, not the millions of different colors found in nature.

But despite that, we see more than 3 colors when we look at our smartphone screen

Well, no, in fact, our eyes see only 3 colors, and our brain, of these 3 colors, is able to recreate hundreds of thousands of them. This is because our eye itself can only distinguish 3 color bands. At the back of the eye, in the retina, we have sensors called cones, which are sensitive to light over a range of different colors. He insisted that the cones are not sensitive to colour, only to the amount of light. Simply put, the so-called blue cones see only violet, blue, and green light. They see neither yellow nor red. On the other hand, red cones are sensitive to green, yellow, and red light, but not to blue or violet. Suddenly, if red light is received by the eye, the brain is receiving an electrical signal from the red cones only and not from the blue cones, and so it knows that the light the eye is receiving is red.

And we have three different types of cones, right?

Yes, blue and red, which I just talked about, and we also have green cones, which let you see the intermediate colors. Suddenly, by analyzing the relative value of the electrical signals sent from the three types of cones, the brain is able to distinguish different natural colors, up to two million different shades. The principle of color images is to send three images with three different eye colors, assigned to each of the three types of cones. The idea is that by playing on the relative intensity of the three colours, we should be able to trick the brain into recreating all of the natural colours. Except it’s not, because our blue, red, and green light sources don’t have the same properties as the cones in our eyes. The result is that with our monitors, color photos, or printers, we reproduce less than half of the natural colors.

But what colors can we not reproduce?

These are, for example, the brightest shades, the so-called metallic colors, or also fluorescent colors. In fact to get it on a picture, you have to register the true colors of nature, not just three intermediate colors.

And this, do not know how to do it?

Yes, there is a process called interferometry, which was invented more than 130 years ago by the French Gabriel Lippmann, who also received the Nobel Prize in Physics. a process that was perfected at the Faculty of Sciences in Lille by another physicist, Auguste Bonsuet. So this operation was not commercially successful, but we find pictures taken by Auguste Bonsu, still visible for a week in the exhibition dedicated to them in Villeneuve-d’Ascq. What is unusual when we look at these images is that we immediately realize that they have a color rendering that has nothing to do with the usual images. If you get the chance, go for it, it’s very rare that you’ll be able to access overlapping images, simply because there aren’t that many of them. It’s free, and I put all the information on the site ramenetascience.fr.