Questions about the size (megabytes) of images from Canon 1D

Discussion in 'Canon' started by Al Dykes, Sep 24, 2003.

  1. Al Dykes

    Al Dykes Guest

    The specs for the 1D say it's 36 bits/pixel. Times
    11 million pixels is 50 Megabytes.

    The specs page on dprevew.com says that the raw files are about 8.8MB.
    I can't see a compression algorithm that gets a lossless 6:1
    compression. The dpreview web site is a little vague. I'm reading
    it as "maximum quality" images.

    Where's the difference ?
     
    Al Dykes, Sep 24, 2003
    #1
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  2. Al Dykes

    Flux Guest

    Canon 1D is 4 Mpixels and produces RAW files of about 4 MB, so I'll assume
    you actually mean the 11 MP Canon 1Ds.

    In RAW format only the sensor information is recorded - in a Bayer sensor
    that means one 12-bit colour for each pixel. 12 bit * 11 MP = 16,5 Mb. So
    the (lossless) RAW compression is actually about 2:1.


    Flux
     
    Flux, Sep 24, 2003
    #2
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  3. No, it's 12 bits of resolution for the one colour that is recorded at
    each pixel. This probably gets interpolated to 12 bits of each colour
    at each pixel inside the raw converter, but the file stored on the card
    is only 12 bits/pixel. That's 16.5 Mb, not 50.
    Which requires only 2:1 compression.

    Dave
     
    Dave Martindale, Sep 26, 2003
    #3
  4. Al Dykes

    Al Dykes Guest


    Isn't it 12 bits per color channel * 3 channels * 11,000,000 pixels
    = 396 million bits
    = 50 million bytes.


    Is there something I'm mission here.

    Yes, I did mean 1Ds instead of 1D.
     
    Al Dykes, Sep 26, 2003
    #4
  5. Al Dykes

    Ray Fischer Guest

    Yes. There aren't three channels for each pixel. There's only one.
    Alternating between red, green, and blue.
     
    Ray Fischer, Sep 27, 2003
    #5
  6. Al Dykes

    Al Dykes Guest

    Lets make sure we are all talking abot raw format.

    I'm using "channel" in the way photoshop does. Maybe that doesn't
    apply while it's still in the camera, If R,G, and B "alternate" it's
    still 36 bits per pixel times 11 million pixels.

    I clearly nead to do some reading. cam someone point me to a web page
    that describes this aspect of the sensors? The page on raw image format
    on dpreview.com is a little too terse for me.


    Thanks
     
    Al Dykes, Sep 27, 2003
    #6
  7. Al Dykes

    Ray Fischer Guest

    I am.
    So am I.
    Not in RAW format. For the 11MP sensor in the Canon 1Ds there are not
    36 bits per pixel. There are only 12 bits per pixel.

    Try this explanation...

    Take two RGB pixels, 36 bits each. Discard the green and blue
    channels for the first. That's 12 bits left. Discard the blue and
    red channels for the second. That's 12 bits left. Repeat.
    What's left is the 12 bits per pixel of the RAW format..
    This ine isn't bad, but you can find more by using Google to seach on
    "bayer pattern red green blue".

    http://www.peter-cockerell.net:8080/Bayer/bayer.html
     
    Ray Fischer, Sep 27, 2003
    #7
  8. Al Dykes

    JPS Guest

    In message <bksd8m$9rd$>,
    That's not exactly right. In the RAW data, it's 12 bits per pixel.
    The 1D is a 4mp camera. You're thinking of the 1Ds, which is 11mp.

    --
     
    JPS, Sep 28, 2003
    #8
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