Different card capacity depending on ISO setting?

Discussion in 'Beyond the Basics' started by colintinto, Aug 22, 2005.

  1. colintinto

    colintinto TPF Noob!

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    Hi Guys,

    Discovered something slightly strange at the weekend. With my 300D, and an empty 1Gb memory card, in RAW mode, it estimates it has space for 140 pictures at ISO 100, but only 119 at ISO 1600.

    I think I have an explanation - 'noisy' pictures don't compress as easily as clean pictures, as there is effectively more detail, even if it's unwanted detail.

    I've noticed that with video - recording an anaog TV programme that's slightly fuzzy takes up more space than one with a nice clean signal.

    Does that sound plausable? I didn't think they'd take that into account when calculating how many images would fit...

    As an aside, took quite a few pics at ISO 1600 at the weekend, and I was impressed at how little noise there was!

    Colin
     
  2. hobbes28

    hobbes28 Incredible Supporting Member

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    That would sound plausable but the RAW image is uncompressed. The estimation for how many shots you can take are just that, an estimation. The size of a picture depends on the colors, detail, lighting..etc. When you take the picture at ISO 1600, you're already adding in the details that will be picked up by having a speed that's that much faster so it's making an estimation based on the potential to pick up more information.

    Hope this helped.
     
  3. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    I've also heard that the actual image can affect file size. For example, a very busy scene with many color/shades etc. will be bigger than a shot of blue sky.
     
  4. Marctwo

    Marctwo TPF Noob!

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    I don't know of any raw formats that are not compressed - they just use a less efficient lossless algorithm.

    If they weren't compressed, you'd only get about 40-50 shots on a 1GB card.
     
  5. Meysha

    Meysha still being picky Vicky

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    True! This happened to me yesterday. I was taking photos of chocolates but because I can only use my flash in manual mode it takes me a couple of shots to get the flash at the right strength. So a couple of pics were completely blown out - just white, they were a lot lot lot smaller than the well exposed, lots of detail and colour pictures.

    Which makes sense, because there's less data therefore smaller file size.
     
  6. NeoDude

    NeoDude TPF Noob!

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    I disagree. You would be able to fit about 160 uncompressed 6 Megapixel images on a 1GB card.
     
  7. tr0gd0o0r

    tr0gd0o0r TPF Noob!

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  8. Marctwo

    Marctwo TPF Noob!

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    How do you work that out?

    At 36bit each pixel is 4.5 bytes if stored efficiently, so 6MP = 27MB at the very least.
     
  9. Meysha

    Meysha still being picky Vicky

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    Hmmm... That sounds like too many to me. Are you sure they're not compressed jpegs? Or are you sure you're shooting at the full 6MP?
     
  10. NeoDude

    NeoDude TPF Noob!

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    Ignore me. I was being stoopid. I was taking a 6mp RAW file to equal 6MB.
     

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