Difference between RAW files?

Discussion in 'Digital Discussion & Q&A' started by ClarenceW, Nov 24, 2006.

  1. ClarenceW

    ClarenceW TPF Noob!

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    what is the significant difference between different RAW files.
    I've got a Olympus E-500, and the RAW files are ~15mb and on Nikon, I've heard they're only ~5mb. Why is this?
     
  2. toastydeath

    toastydeath TPF Noob!

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    First, you should get two RAW files side by side before assuming one is that much smaller than the other.

    The differences between various RAWs are simple - RAW is not a standard format like JPEG is. RAW is whatever data the CCD in the camea dumps out, without any modification. Different cameras have different hardware systems inside, so each RAW file will be different. Whereas JPEG is a standard format, and everyone is required to write the same kind of data in the same way to maintain interoperability.
     
  3. markc

    markc TPF Noob!

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    This is a common misunderstanding. RAW files are still in a format; there's just a lot of different ones. It's not reliant on hardware. Two Canon cameras with different sensors may still save the data in the same RAW format. Some cameras will even modify the data a little before writing, but it is as close to unprocessed as you get from a consumer camera. There's probably some marketing reason for manufacturers to not want to agree on a single format.

    The main difference between the RAW format and uncompressed TIFFs is that RAW gamma is linear and TIFF is on a curve to match eye sensitivity. Another big difference between RAW and JPG is that most RAW files are 12-bit and JPEGs are 8-bit. TIFFs will hold even more color data at 16-bit.

    Trying to compare sizes is going to be difficult. The larger the sensor the more data there is that needs to be stored, but different manufacturers are going to be using different compression schemes. They will be lossless, like RAR and ZIP, but they will be balancing write speed vs. final size. The more compression, the more processing time it will take. That's why cameras won't write at the full rated speed of the cards they use.

    http://www.luminous-landscape.com/tutorials/understanding-series/u-raw-files.shtml
     
  4. True, if your camera's settings (not the pre-sets like "portrait" or "landscape") are set for a certain level of sharpening, saturation, contrast, etc then the RAW file will record that - but they can be changed on the computer.

    If you have an 8 megapixel camera, then your RAW file will be 8 MB in size.
     
  5. markc

    markc TPF Noob!

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    I meant that some data manipulation, like trying to fill in dead pixels or some basic noise reduction, can still be applied directly to the data that gets stored in a RAW file. It all depends on what a manufacturer wants to do. There's no guarantee that it's exactly as the sensor sees it. As far as I know, RAW stores data as RGB. There are very few sensors that actually have RGB combined locations. Most have a series of discreet and alternating R, G, and B and use an algorithm to come up with RGB values for a final pixel location based on its neighbors' values.

    http://en.wikipedia.org/wiki/Bayer_filter
     
  6. toastydeath

    toastydeath TPF Noob!

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    I believe you missed what I said while jumping to call it a misconception.

    Any data that isn't random must have some format to it in order to be written and read later. I specifically stated "standard format" instead of just "unformatted." In IT and computer science, a "standard format" means data is arranged in a common, agreed upon way so programs may read and write the data easily. JPEG, PNG, ODF, et cetera; they're all going to have the same structure as per the standard. RAW has a different data structure per manufacturer and, in some cases, hardware implementation. You not only must know that the data is RAW, but what particular flavor of RAW it is. The applications that can read a variety of RAW files have a fair bit of programming behind them to determine which manufacturer's RAW you are reading based on the data structure. It is then assigned to the correct plugin or library for that format. On the other side of the coin, JPEG is JPEG. You look in the JPEG standard for information on reading/writing it and don't need complex logic to figure out what kind of file it is.

    Thus, RAW is not a standard format.
     
  7. Alex_B

    Alex_B No longer a newbie, moving up!

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    I totally agree that current RAW formats are everything but standard formats ...

    I reccommend reading the following:

    http://www.openraw.org/
     
  8. markc

    markc TPF Noob!

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    The term "standard format" isn't what led me to that assumption, it was the lines:
    and
    which isn't the case as I understand RAW. Otherwise there wouldn't be a push for an single open RAW format. I was agreeing that there is no standard RAW format. I was disagreeing with the idea that a RAW file is data written straight from the sensor with no manipulation. Some may be, but they would have to be in the RGBG format, not RGB, and it wouldn't be all RAW files.

    I may be wrong, and I'm sorry if this came across as snotty, but that's how I understand it. If there is data out there that contradicts this, I honestly would like to see it, but it would have to apply to all RAW formats, not just one of the many.
     
  9. abraxas

    abraxas No longer a newbie, moving up!

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    Here's an exerpt from a discussion about raw you may find interesting.

    All digital cameras designed for professional use can produce 'raw' images, that is files that contain the actual data produced by the photo sensors in an appropriate digital format. ...

    http://photography.about.com/library/weekly/aa061603a.htm
     
  10. markc

    markc TPF Noob!

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    Thanks for that. So it does look like it saves each individual color value separately (one value for G, then one for R, then one for G, etc., then next row alternating between B and G). This is different than I understood it. Luckily this doesn't prevent a single format though, as long as they put information in the header as to how the data was arranged.

    I still maintain that this doesn't mean that there isn't some manipulation going on before the data is stored, but it does mean that a large chunk of what I thought was getting interpolated isn't happening in the camera. I'm not saying that there *is* manipulation, just that we can't know unless the manufacturer decides to tell us. I guess I'm being picky.
     
  11. Tiberius

    Tiberius TPF Noob!

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    As other have said, RAW file sizes depend on a lot of factors - size of sensor, the specific image (how much detail is in it), etc., etc., and it's not a standardized format.

    Also, Nikon compresses their RAW files (lossless compression, like a ZIP file, not like an MP3/JPG file), so that could be part of the difference.
     

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