File size ?

Discussion in 'Digital Discussion & Q&A' started by ottor, Aug 10, 2009.

  1. ottor

    ottor No longer a newbie, moving up!

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    Lets say I take 3 RAW photographs in a row ..... they'll end up being of different sizes ... What factors determine file size ? Color, or complexity of composition??

    Nothing I really need to know .... Just something that I've puzzled over since someone asked me that question ....

    I just told them that the file size is bigger if you take a picture of a bigger thing... Small things have small file sizes ... he went away..;)

    tks,

    r
     
  2. Big Mike

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

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    I don't know for sure...but it seems that 'busier' photos tend to be larger files. Just a guess.

    Probably a more accurate guess would be that brighter photos (or areas of a photo) are digitally bigger because they carry more color information. This is why I like to 'shoot to the right'.

    Expose Right
     
  3. Dwig

    Dwig TPF Noob!

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    The actual RAW data block in the file will not change size from picture to picture in uncompressed RAW files. If the RAW format is a compressed format (e.g. Nikon NEF files can be either compressed or uncompressed, some cameras offer a choice others don't). The header information will also remain constant unless you use some of the special functions found on some cameras to add text or sound notations. The only other component of RAW files that will change from shot to shot is the embedded JPEG preview.

    Compression amount, both the compression of the RAW data and that inherent in the JPEG preview, will vary shot to shot based on the nature of the image. JPEG compression, like most, is highly affected by the amount of detail in the image, either real subject detail or artifacts like noise.
     
  4. Garbz

    Garbz No longer a newbie, moving up!

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    Depends on the compression algorithm. Some lossless compressions do horridly with detail, but very well with patterns, some do horribly with any detail at all. Some lossy compressions drops the bitrate, some annihilate the detail in the blue channel (our eyes are very non sensitive to blue).

    Every photo is different, and unless you are explaining every pixel individually with no compression, every RAW will be a different size.
     
  5. astrostu

    astrostu I shoot for the stars

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    At least with the camera RAW format from the Canon 350D, all the RAW files are nearly identical in size. All uncompressed TIFF files will also be identical in size from any software. All JPEG files will be different sizes. It all depends on the compression algorithm, if there is any applied. If there is no compression, then it is based solely upon number of pixels, bit-depth, and number of color channels.
     
  6. UUilliam

    UUilliam TPF Noob!

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    I can rule out that the pixels hold different pixel data...
    If you make an image that is 100% white at 100x100 it will be the same size and an image with a different colour for each pixel at 100x100
    even if you make an image with no colour at all.

    Source: Adobe Illustrator cs4 Tutorial (from linda.com)
    cant remember which.
     
  7. astrostu

    astrostu I shoot for the stars

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    This is only true if there is no form of image compression, as I stated above. Think of it this way, with three sheets of paper:

    (1) The first sheet has the letter "A" printed all over it.

    (2) The second sheet has English text printed over it.

    (3) The third sheet has random English alphabet characters printed all over it.

    Using an uncompressed TIFF algorithm to write that text, it would simply write every character as-is. Each sheet would take the same amount of data to store it.

    Now let's say you used an algorithm that compressed based upon patterns. It sees the, say, 1000 letter "A" all in a row and can simply store this data as "1000xA" -- very short. It can recognize patterns in the English text in the second example and save every word "the" as a special character, thus helping to shrink the size of the text. But in (3), there is no way it can compress it, so saving that page would take up the most space. In this sense, every "image" (page of text) even though it's the same size will take up a different amount of space because it is compressed based on its content.

    The same is true for pictures. If you have a quarter of your picture as over-saturated sky (so it's all white), then it is very easy for any even rudimentary compression algorithm to simply write that whole block as a giant rectangle that's just filled with "white" (255, 255, 255) if RGB 8-bit color as opposed to writing out the value of every pixel. And this is just a "lossless" compression.

    In "lossy" compression schemes, the algorithm can cheat. Say there's a little bit of a tree sticking up into that white sky. A lossy algorithm may say that tree is too small to worry about and just ignore it, writing over it with the white sky to save room. Alternatively, it may decide to save a little bit of it as just a single-color straight line. This will take more information since it has to remember that, but it will take less than recording every single pixel value as it was originally. Hopefully you get the idea.

    So again, it all depends on the compression algorithm, if there is one employed.
     
  8. DRB022

    DRB022 TPF Noob!

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    So what is RAW+B?
     
  9. Josh66

    Josh66 Been spending a lot of time on here!

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    I've noticed that high ISO RAWs are bigger...
     
  10. musicaleCA

    musicaleCA TPF Noob!

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    RAW plus Bobblehead!
     
  11. Garbz

    Garbz No longer a newbie, moving up!

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    That is because dark parts of an image are most easily compressed in a lossy algorithm. However when you introduce noise all of a sudden there's detail. The extra size is the attempt of the compressor to preserve the noise detail in the image.
     
  12. DRB022

    DRB022 TPF Noob!

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    lol that's why we don't post right after we get home from the bar
     

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