Why you can't take a good picture of a rainbow

I found out recently that I was wrong about something which is fascinating because it's never happened before it's never happened before I had this really interesting fact that I would tell people about the way screens work like computer screens TV screens phone screens and it turns out is completely wrong so you might know that a computer screen is made up of pixels and each pixel is made up of three sub pixels that are red green and blue in color and the brightness of those three sub pixels is adjusted to trick you into seeing all the colors in between red green and blue and it really is a trick by the way like if the monitor wants you to see yellow then it will dial up the brightness of the red sub pixels and the green sub pixels and you will experience that as yellow I can recreate that effect here with torches so I've got a red and a green torch when I overlapped them I see yellow I'm experiencing yellow in the overlap but there is no yellow light going into my eyes there is no light with a yellow wavelength entering my eyeballs so there's obviously some kind of trickery going on there which I'll get to in a minute but just for completeness let's first look at all three sub pixels red green and blue but with torches so red green and blue are called the additive primary colors I mean they add together they make white so look all three together makes white and in the crossovers you've got yellow we've seen that already you've got cyan that's when blue and green are added together and you've got magenta that's when blue and red are added together the opposite ends of the spectrum added together without green and you may recognize those three crossover colors cyan magenta and yellow from your printer that's why they're called the expensive primary colors they're also called the subtractive primary colors because you subtract them from white you start off with the white sheet of paper that's all colors mixed together and then by laying down pigment like magenta you're actually subtracting color from the page so for example with magenta you've got white light shining on the page magenta absorbs green it subtracts and reflects blue and red so how does this trick work where a computer monitor can make you see all these colors just using red green and blue light well it turns out this ability to mix colors together and get other colors has nothing to do with physics and everything to do with biology it's to do with how your eyes work so you might know in the back of your eyes you've got these cells called cone cells and these are the cells that are responsible for your perception of color you might also know that you've got three types of cone cells in your eyes and for this video I'm actually gonna oversimplify things a little bit because in my next video I'm gonna dive into the amazing where that cone cells work it's so interesting but for this video let's just say we've got three types of cone cells and we're gonna call them red cone cells green cone cells and blue cone cells so and again I'm oversimplifying but the red cone cells are sensitive to the red part of the spectrum the blue cone cells are sensitive to the blue part of the spectrum and the green cone cells are sensitive to the green part of the spectrum but you'll notice that the sensitivity of these different cone cells overlap each other so when yellow light enters your eyes it stimulates your red cones a little bit and your green cones a little bit so your brain is receiving a message or maybe your visual system is receiving a message from your red cones and your green cones simultaneously and your visual system interprets that information as yellow light which is great that's amazing your brain has deduced something about the world that it can't perceive directly you don't have cone cells specifically for yellow light but you've been able to interpret yellow light coming into your eyes but it does mean that your visual system can be tricked and that's what your computer screen is doing is what I was doing with the torches by stimulating your red cones with red light and your green cones with green light you see the color in between you see yellow light because that's what your brain is wired to do so that's the background here's the fact that I was telling people a computer screen cannot recreate the experience of seeing violet light because if you think about it you've got red green and blue sub pixels and you can change the brightness of those sub pixels to reproduce the experience of any color in between red green and blue but the rainbow goes red orange yellow green blue indigo violet indigo and violet are outside of the gamut of possible colors you can create with RGB with red green and blue sub pixels so if you want to experience violet you have to go out into the real world it's a terrifying place but it has rainbows and rainbows have violet in them or you could look at something that's violet like a violet of course this violet that I'm showing you on the screen is a poor imitation of the real experience of looking at an actual violet because a computer screen doesn't have violet pixels it can only show what's between red and blue and if you've ever seen an illustration of the color spectrum on a computer you may have seen something beyond blue that looks like this it looks like magenta and that's just where the illustrator has kind of bodged it they've put magenta there in place of violet because they don't have violet pixels to play with except that I'm completely wrong a computer screen can recreate the experience of seeing violet in the real world but how can that be well it turns out that actually if you look at a rainbow and you look beyond blue it kind of does look like magenta and that's because the way cone cells work isn't quite as straightforward as I described if you look at the sensitivity spectrum of what we're calling red cones well there's a big bump in sensitivity on the red end of the spectrum as you would expect they're sensitive to red light but because of a quirk of biochemistry there's also a second smaller bump over in the far blue part of the spectrum so when violet light is shining into your eyes it stimulates your blue cones and your red cones at the same time in other words when you look at the violet part of a rainbow what you're experiencing is the same as what you're experienced if there was red and blue light shining into your eyes at the same time in other words magenta and that's how a computer screen can recreate the experience of that far end of the rainbow he just needs to dial up the red slightly so yeah I was wrong I don't even know I heard that fact maybe I came up with it myself which is terrible that's like a really bad way to do science just have a think about something guys probably true there is still a sense in which it's challenging to faithfully recreate the experience of seeing a rainbow digitally and it's not to do with the display that you use it's to do with the camera that you take the picture with so you may know that a camera sensor also has pixels but they're sensing pixels as opposed to light-emitting pixels they're still called pixels and they have red green and blue sub pixels that are sensing the light coming into the lens and if you're a camera manufacturer then you want your pictures to faithfully reproduce the human experience but that's actually really hard to do and it turns out some cameras don't really faithfully reproduce the absorption spectrum or the sensitivity spectrum of the human cones I recreated a rainbow in the garden using a hose when the Sun was out and with my GH five you can see there is that magenta just beyond the blue so it looks as though the red pixel sensors in my G H 5 do have that second bump of sensitivity in the far blue my Panasonic gh2 seems to have that second bump but interestingly the GoPro the GoPro Hero 7 at least the one that I've got doesn't show magenta at the end of the rainbow if you take a picture of a rainbow with a GoPro Hero 7 violet will disappear it will just look just to confirm that I've got a laser pointer here it's 405 nanometers which is violet in my th5 you can see that's kind of working quite well in some senses is a bit too much red there but look in the GoPro Hero 7 it's just there there's there's no violet there it's just blue because it's quite difficult to take a picture of a rainbow anyway because they're actually quite faint and quite thin I've got this thing it's a spectroscope so any light that shines into this slit here is split up into its component wavelengths a bit like a prism except it uses diffraction this is what white light looks like through my GoPro and you can see there's only blue there there's no violet / magenta it's also interesting to see how quickly it transitions from cyan to blue it's very sudden this is what it looks like to the gh 5 which is a bit better so there you go it's difficult to take a good picture of a rainbow and that's way an interesting consequence of all this is I had a problem when I first started investing in cameras and lenses and lights I got this big light box and I haven't bought a lot of complex for essent light bulbs to go in there because that would be a nice way to like myself right that's studio lighting and the bowl was look white but if you look at the light through the spectroscope you can see that actually it doesn't have that nice even distribution of wavelengths that you get from the Sun but in general that wouldn't be a problem like if you were looking at me in person oh I would look normal there's an incompatibility between the weirdness of these complex present bulbs and the weirdness of the sensor in my camera well I'll just I'll show you so here I am illuminated just by the complex four are some bulbs and you can see that I'm a little bit green it's weird it's new I just couldn't figure it out for so long because the light doesn't look green and it doesn't make other things look green it's just the way it interacts with the pigment in my skin and the sensor in the camera in the end I just decided to switch to led panels have got these LED panels here just to see if that would make a difference and it did it turns out the spectrum from these LED bulbs is a lot smoother a lot closer to the spectrum of white light from the Sun and I use this now just to light the room for the sponsor missus this week I thought I'd share an embarrassing story we're on the subject of getting things wrong which it turns out I did quite a lot the sponsor is dashlane the password manager and the embarrassing story is about how I fell for a phishing attack this is a few years ago now I've got an email that appeared to come from Microsoft and it mentioned a friend of mine by name and it said that they wanted to share an album of photos with me through onedrive so I click on the link and I log into onedrive except that I don't log into onedrive of course instead what I do is I give my Microsoft credentials to a malicious person and then they logged into my hotmail account presumably automatically and sent out similar emails to all of my contacts so you can see how the the loop is closed there and the reason it's embarrassing is because I like to think that I don't fall for that sort of thing except that on this occasion the friend in question we just been to a wedding together so it makes sense that they would want to share an album of photos with me and the fête website was really good and I was jet-lagged the point is you only have to let your guard down once like if that had been my Google account it would have been absolutely disastrous you've probably already heard a lot of the benefits of using a password manager but you might not know that password manager can also protect you from phishing attacks because if you think about it if you're only using your password manager to fill in your online credentials well a password manager isn't going to fall for a fake website it's not going to fall for a look-alike URL it's gonna check the ssl certificates of the website that you're on in other words a password manager is never going to fill in your details on a phishing scam website will a password manager give you 100% protection no is it better than not using a password manager definitely yes and really that's all that matters I used dashlane recently to change a whole load of my lame passwords and a whole bunch of websites so I don't need to worry about password reuse attacks anymore like if one of those services gets compromised it's not an issue some of the other features that I like it syncs with your phone you can share logins with people without them even knowing the password and it will autofill forms for you including credit card details so it's a real time-saver if that sounds useful to you you can try it for free on your first device whether that's your laptop or your phone by going to - Lane comm forward slash Steve and if you like it and you want to upgrade to premium you can get 10% off using my code Steve when you check out I hope you enjoyed this video if you did don't forget to hit subscribe and I'll see you next time [Music]

Channel: Steve Mould

Views: 510,840

Rating: 4.9436932 out of 5

Keywords: Explained, understand, subpixels, rgb, red green blue, violet, indigo

Id: HauiF_AQUIY

Length: 14min 19sec (859 seconds)

Published: Thu Sep 19 2019