How do digital cameras work? | James May Q&A | Head Squeeze

How do digital cameras work? | James May Q&A | Head Squeeze


How do digital cameras work? The camera is
one of those wondrous inventions that changed the world. Before it arrived the only way
to make a picture was to draw it or paint it. Which obviously removed a fair amount
of the spontaneity when you were trying to knock out a quick selfie of yourself giving
epic duckface while eating a Maccy-Ds with your bezzie mates. Which is probably why Rembrandt always looked
so depressed in his self-portraits. Anyway, the camera made it possible to make an instant
picture in a fraction of a second. But the process involved in getting the image out
of the camera and printed was a complicated one. The light-sensitive film had to be carefully
removed, sent to a processor, get developed, turned into a negative and then printed onto
photographic paper. In the dark. Which was a problem with the rise of the digital
age, the internet and your pressing need to upload a picture of Fluffy to the ‘my cat
looks like Hitler’ web forum. But while the microprocessor revolution started
to transform many parts of our lives from the 1970s onwards, the digital camera was
a relatively late invention, arriving after the video camera, the mobile phone, the laptop
computer and even the Billy Big Bass singing plastic fish. This was because the technology
that lies at the heart of it, the sensor chip, is unbelievably complicated. In a film camera, light is sent through a
lens and a shutter onto photo-sensitive film. Which, with a subject shot in normal light,
needs just hundredths of a second of exposure to capture the image. The front end of a digital
camera works on exactly the same principle, light is focused through the lens and controlled
by a shutter and variable aperture. But instead of film, there’s a light-sensitive sensor
chip that has to record all of the data in a very short space of time. There are different ways of doing this, but
we’re going to concentrate on the CMOS or Complementary Metal Oxide Semiconductor sensor
that now sits in the majority of digital cameras, from those integrated in phones to fairly
chunky DSLRs (that’s Digital Single Lens Reflex in the jargon) their the sort that look like
‘real’ cameras. The camera’s sensor is covered with tiny individual
light sensitive cells, each of which can measure the amount of light that falls on in. As the
digital camera has evolved, so have the number of these pixels on the surface of the sensor. Ten years ago, you’d struggle to get a digital
camera capable of delivering much more than a single ‘megapixel’ of resolution, a million
total pixels, or a grid 1200 by 900. But these days, 12 or 16 megapixels are commonplace
among top-spec ‘prosumer’ and professional camera. That’s enough to enable you to produce
images the size of a magazine cover with no loss in perceived quality. The cells act like the photosensitive chemicals
on old-fashioned film, reacting to the light that falls on them and then reporting to the
camera’s microprocessor brain. That would be fine for the sort of moody black and white
shots favoured by gothy Instagram users. But, because most of us want to post pictures of
our lunch to Facebook in colour, it’s also necessary to split the light ‘seen’ by the
camera into the three primary colours which can then be used to create an accurate image. There are different ways of doing this: some
expensive cameras will even employ three different filters. But most CMOS sensors will use what’s
called a ‘Bayer Filter’. This is a grid of coloured filters that sit over the sensor
with red, green and blue elements over individual pixels that will only allow their respective
light colours through. Because the human eye is most sensitive to green light, which largely
determines how ‘bright’ an image looks, there are twice as many green pixels as red or blue.
The filters are arranged in a clever mathematical pattern, which means that the camera’s brain
can interpolate using a demosaicing algorithm. Yes, really. Or, in slightly plainer language, the camera
doesn’t just look at an individual pixel on the sensor, it also looks at the pixels around
it to come up with an informed guess of what the true colour of that pixel is. Although even the most advanced sensors in
the world still struggle with the increasingly unlikely colour of Richard Hammond’s hair.

100 thoughts to “How do digital cameras work? | James May Q&A | Head Squeeze”

  1. Megapixels are great. But they're also misleading. Did you know 35 mm film has detail equivalent to about 35 megapixels? For that matter, 'full frame' film cameras produce images exceeding an effective resolution of 100 megapixels. But… This doesn't take into account yet that the 'megapixels' of a digital camera aren't proper pixels… a colour pixel needs to have an RGB value. And the 'megapixel' rating counts each red, green & blue pixel element as individual things. (Which would be correct in a black & white sensor, but is wrong in a colour one).
    This means the actual 'resolution' of a digital camera, when compared to say a computer screen, is only 1/3 of it's 'megapixel' rating. (or 1/2 at most if you consider the image processing.) – I'm staring at a computer screen with the (for current computers) rather low resolution of about 1 million pixels. But, to get a good quality picture that takes up the whole screen without any missing detail, it would require a 3 megapixel camera…

  2. It's not true that ten years ago you'd struggle to get a digital camera with more than 1 megapixel. I bought my first digital camera in 2004, an HP Photo Smart R707, which I still have, and it had 5.1 megapixels.

  3. Sorry, I can't watch this video without getting furious about that they didn't use a monospaced font for the time shown on the camera!! :S

  4. Err plus "10 years ago struggle to get a MegaPixel" ???

    Canon EOS 300D, revolutionary and came out in 2003 with 6.3MP sensor and was under a grand.

    The people who write his script really need to search the interweb before Mr May gets to read it out, makes him look like he doesn't really know his subject.

  5. Finally a video with James May again! I signed up for James May, you know? And I will not watch any videos without James May! Exclamation Mark!

  6. Who wants to see James May on camera?

    Driving a Koenigsegg Agera R.

    At 270+ MPH.

    While Clarkson and Hammond shit themselves silly.

    And The Stig, just stands there in the background. Being "The Stig". And nothing else…

  7. Sorry James (or, more properly, Head Squeeze researchers), Big Mouth Billy Bass came out in 1998 while I definitely had a digital camera in 1996 (the Kodak DC25, I've still got it packed away somewhere) while my middle-school buddy had the Apple Quicktake 100 at least a year earlier (it was released in 1994). And these were just the early COMMERCIALLY available digital cameras, extremely expensive professional digital cameras existed before that.

    Also worth noting that the primary reason CMOS (pronounced SEE-moss) sensors are so ubiquitous is that it's far less expensive and less power-hungry than the CCD varieties. The downside being that it actually has to observe the image one line at a time (kinda like a scanner) which, on particularly cheap cameras like those found on phones, can result in distortion effects when the camera and subject are moving in relation to each other (see http://en.wikipedia.org/wiki/Rolling_shutter ). CCD, on the other hand, takes a snapshot of the scene so you don't get this effect (though you do get other effects such as when a point light source is bright enough you can get a vertical smear as the electrons spill over into neighbouring cells).

    Of course the ubiquity, low cost, and low power use of CMOS means that there has been far more R&D on it than CCD which has resulted in some very high quality CMOS sensors that don't have nearly as much distortion as their cheaper siblings which is why you can even find them in high-end professional DSLRs.

  8. the constant flickering of position by the time elapsed was a bit distracting, the text probably shouldn't have been auto aligned in every frame

  9. that is so funny, this is a british-produced show, but it is very transatlantic in its cultural references.  I wonder if peopel high-up are trying to merge the cultures of Britain and America to make Oceana?

  10. A 16mp camera will not allow you to produce large images with no loss of perceived quality unless it comes from a large enough sensor, the same way you could not do the same with 110 film no matter how fine a grained film you used, you can't cheat the system.

  11. Oh Cock! He was reading the explanation for the Megapixel from the Wikipedia article on Pixels 😛
    Here you go,
    http://en.m.wikipedia.org/wiki/Pixel

    And no, I'm not fun at parties.

  12. So why do we call the camera "digital"? It uses digits, but how? What's behind a pixel? It works through the binary system? Thanks a lot.

  13. around minute 4, he says human eye is most sensitive to green and its conceived as brightness, its wrong. human eye is most sensitive to BLUE and yes it is conceived as brightness. I know it because I do TV calibrations. this is why in stores TVs are pumped up on blue. and if you use your phones or laptops calibration setting and take away all blue youll see a brownish looking picture.

  14. well James this from Dominican Republic me and my family are fans from you and your partners of top gear and we are missing that glorious trio in top gear the new show is as bad as top gear usa we really sorry and we miss the real program and yourselves

  15. James May can you please explain to us why many people take very annoying vertical video instead nice horizontal video?

  16. it felt like I was watching some alien transcript about some super super advanced technology beyond human comprehension

  17. Hi @Brit Lab I have one. Why and how lips are as they are. Like why does is separate half inside the mouth and the other outside? How does the skin drying out works? – and why it happens, doesn't they lubricate themselves like the rest of the body? Why are some bigger than another persons? – and why is the lower lip always bigger?

  18. I've been watching Top Gear for years and it is only now that I discover that May had a show on Youtube this whole time? What sorcery is this?!?!?

  19. Daily reminder that I fancy myself smart but am in fact not even half as well educated as people in STEM today. No worries, I'm content staring blankly in awe at the achievement of others.

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