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  1. #31
    BetterSense's Avatar
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    No way are they analog. They have a discrete, fixed amount of photo sites on the sensor. If CMOS sensors are 'analog' then films are 'digital' because they work with individual electrons.

  2. #32
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    Quote Originally Posted by BetterSense View Post
    No way are they analog. They have a discrete, fixed amount of photo sites on the sensor. If CMOS sensors are 'analog' then films are 'digital' because they work with individual electrons.
    A digital circuit is one that can only be on or off. This is the source of the ones and zeros that form the foundations of computer code. A modern computer is basically a big bunch of circuits that can only be on or off, and turning the right ones on and off in the correct order will produce an image on a screen, send data through the internet, etc.

    Your standard household circuits, however, are analog - the circuit can be on or off, but it also has varying levels of "on" - for example, 110 volts can be run through the circuit, but so can 120 volts, etc. More voltage will make your lights brighter and your electric range hotter. So, varying levels.

    CMOS and CCD sensors are analog because they produce output signals that are varying, not simply on or off. Each individual pixel will output a greater strength signal if more photons hit that sensor. So, therefore, just like the household circuits, there are varying levels of "on" for each pixel.

    The "digital" in "digital camera" comes after the CMOS or CCD sensor produces signals. There is a chip in a digital camera that converts those analog signals into digital data for storage on the memory card.

    Electronic sensors were used in TV cameras long before digital video cameras came about. The output of the chips was simply never converted to a digital signal.
    Last edited by Poohblah; 01-06-2009 at 06:21 PM. Click to view previous post history.

  3. #33
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    I think SilverGlow was referring to the intensity level of a CCD or CMOS sensor being analog at the pixel site's output, with the digital part of it appearing downstream at the analog-to-digital converter.

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    Quote Originally Posted by ted_smith View Post
    What image capture technology does the Hubble Telescope use? The telescope was launched in 1990 so I am curious to know whether it captures images on film or digital (in light of it's age). If film, what sort? Just curious.
    I think your question may have been answered, but as far as digital imaging is concern, the first patent for solid state imaging device was in 1979

    Check out http://www.google.com/patents?vid=USPAT5298776

  5. #35
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    Quote Originally Posted by BetterSense View Post
    No way are they analog. They have a discrete, fixed amount of photo sites on the sensor. If CMOS sensors are 'analog' then films are 'digital' because they work with individual electrons.
    Uh no. they are analog devices. You can hook them to an oscilloscope and see the waveform. I've done it. They do not read or output anything in an on/off or otherwise discreet state. Photo sites determine resolution, not signal. Also solid state is not synonymous with digital. As I stated before, I have cameras that are solid state- no tubes- but purely analog.

  6. #36
    Photo Engineer's Avatar
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    Well, digital -> analog converters look analog but actually move in steps based on bit count.

    PE

  7. #37
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    Quote Originally Posted by Photo Engineer View Post
    Well, digital -> analog converters look analog but actually move in steps based on bit count.

    PE
    True, but how does that relate to a CCD?

  8. #38
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    Quote Originally Posted by BetterSense View Post
    No way are they analog. They have a discrete, fixed amount of photo sites on the sensor. If CMOS sensors are 'analog' then films are 'digital' because they work with individual electrons.
    Huh? Any given piece of film has a discrete, fixed amount of photo sites on it as well. They're arranged a little more haphazardly than a CMOS/CCD sensor, of course.

    The output of a CCD is indeed analogue. The output then goes through an analogue amplifier (the gain of which is adjusted to alter the sensitivity - i.e. change the ISO,) after which an analogue-to-digital converter quantizes and converts the output to a digital representation.

    (If I recall correctly, what you actually get out of the CCD is an analogue waveform - i.e. you effectively drain the charge in each photosite (the charge collected being proportional to the light falling on the site) in turn* which results in a continuous waveform which is then amplified, and quantized by the D2A both in terms of the level and temporally (i.e. splitting the waveform up between the pixels.))


    * I would assume there is some parallelism involved - i.e. the readout is 'multiplexed' in some way.
    Another day goes under; a little bourbon will take the strain...

  9. #39
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    Quote Originally Posted by JBrunner View Post
    Uh no. they are analog devices. You can hook them to an oscilloscope and see the waveform. I've done it. They do not read or output anything in an on/off or otherwise discreet state. Photo sites determine resolution, not signal. Also solid state is not synonymous with digital. As I stated before, I have cameras that are solid state- no tubes- but purely analog.
    Indeed; the invention of electronic imaging significantly pre-dates digital image processing - that nice Scottish chap Mr Baird was doing it in the 1920s after all .


    (I have a plan to one of these days get round to reproducing a Baird style TV camera and television; a photo sensor, a lightbulb, a couple of LF lenses and a spinning disc or two and the job's a good'un as they say round these parts.)
    Another day goes under; a little bourbon will take the strain...

  10. #40
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    Look guys, everything (as noted above) is digital on the atomic scale. A photon is detected or it is not, on or off! The difference is that in analog photography, 3 atoms (2 electrons) will cause an image to start to form. In 1 mole of silver there are 6.023 x 10^23 (that is 23 zeros) atoms of silver. In a square foot of film that is about 300 mg so the total amount of image forming centers may be 108/.300 / 3 * 6.023 x 10^23. That is a huge amount of "digital" dots. We cannot percieve the number of steps involved. To date, humanity can only make devices that count in 8, 16, 32, 64 and 128 bits or increments. Even the best devices count digitally in steps.

    So, when we refer to digital, it is everywhere, but digital photography is limited by current technology and can't even draw a straight line. It draws jaggies instead. Analog photography draws jaggies but at the atomic level. We cant see them except as very fine grain at high magnification, but we see square pixels in digital images.

    So, everything analog is digital but everything digital is not analog due to limitations in science. The more particles involved in a digital image, the more bits, the more we see an analog response.

    PE

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