How many megapixels are my pics?

Discussion in 'Nikon' started by alex_bartonek, Aug 11, 2006.

  1. just a general question about this.. when I take pics w/my D70S and use the
    highest picture mode without RAW are my pictures 6mp pics (assuming 3000x2000)?

    What about the D80? Since it is a 10mp camera in theory 3200x2000 (or
    whatever size its biggest is) those pics come out as 10mp, correct?
     
  2. Alex,<br>
    <br>
    You can check the file size, the space the image takes on your
    computer, with your computer&#146;s operating system. My guess is
    you don&#146;t know how to use it well. Many programs like Nikon
    View and IrfanView can give you the image size which will be a
    little smaller. Forgive me if I&#146;m wrong but it sounds like
    you need to do some serious studying to better use your camera
    and computer. This is such a simple question to answer with just
    a few clicks of your mouse. The answer is on the computer you set
    this message with.<br>
    <br>
    Best,<br>
    <br>
    Dave Hartman.<br>
    <br>
    PS: I&#146;m not a D70 owner so I can&#146;t check my files to
    advise.
     
  3. I didn't understand you OWN a D80... Well. Then I agree with Dave.
     
  4. David,

    No offense, but I have forgotten more about computers/programming then you will know in your lifetime. Forgive me if I am wrong.

    I am not asking about filesize or imagesize. I am asking if the highest resolution image my camera takes, being 3000x2000(or so) would that be the 6 megapixel image? Simple question. More then likey it is yes but I figured I'd ask.

    Please re-read my post to help you better understand my question.

    Thanks
    Alex
     
  5. Are you talking about file size or image dimensions? Assuming you mean image dimensions, yes.. 3000x2000 = 6,000,000 pixels = 6 mega (million) pixels.

    Knowing that SLRs take pictures in the 2:3 aspect ratio and knowing the D200 is 10mp: 2x * 3x = 10,000,000. So 6x^2 = 10,000,000. So x=1291. So a D200's pictures are roughly 2582*3873.
     
  6. Thank you Brian. Thats what I figured.
     
  7. Alex, You're question is a very good one, and one that I have puzzled over for a long time. My D70 gives images, made on the best JPEG setting, that are 3008 x 2000 pixels; however, the file size for them is NOT 6 megabites, as I woud expect them to be. The file size varies from about 2.20 megabites to 2.85 megabites.
     
  8. its "bytes", and there is no direct coorilation between image dimensions in pixles (megapixles) and the file size.
     
  9. Robert ---"the file size for them is NOT 6 megabites, as I woud expect them to be"

    A quite common mistake ... the assumtion that a pixel in the image would equal a byte in the file is wrong. (So is everything that derives from this assumtion).

    Jpg does a (lossy) image compression ... it doesn't reduce its dimensions, but it does eliminate content and thereby, can reduce the
    size of the resulting file quite a bit.

    Rainer
     
  10. Rainer -- Why then do my D70 raw files vary from 5.49 to 6.22 mb per image (these numbers from one shoot)? Since there is no compression in the raw file, shouldn't it be 3008 x 2000 = 6.016 mb?
     
  11. its "bytes", and there is no direct coorilation between image dimensions in pixles (megapixles) and the file size.
    Sorry, but this is just wrong. One pixel storing 8-bit color information will require 3 bytes (1 byte = 8 bits, RGB each require 1-byte, so 3 bytes). A 16-bit pixel requires twice as much (2 bytes/color). So a 10 megapixel image (10,000,000 pixels) in 8-bit color takes 30 MB to store in uncompressed mode. The 16-bit version (even if the image is only 12-bit or 14-bit, it is still stored as 16-bit) takes 60 MB.
    Now for real life: My coolscan IV give images that are ~10 megapixels. They are saved as uncompressed tiff files, and take up slightly more than 60MB (the pixel size varies slightly, and there is a small amount of overhead information stored with the image).
    If you want to compress things, or store in a lossy format, then the size of the image ultimately depends on the algorithm that calculates the compression. But if you take a compressed image, and resave it in a non-lossy format, you'll be back to the size specified above.
     
  12. Why then do my D70 raw files vary from 5.49 to 6.22 mb per image (these numbers from one shoot)? Since there is no compression in the raw file, shouldn't it be 3008 x 2000 = 6.016 mb?
    I've never used a RAW image, so I may not be right, but I'd guess that the images are compressed. There are ways to do non-lossy compression. Imagine if you have a row of pixels, and the first 20 pixels are all identically the same color. Instead of storing 20 identical pixels (at a cost of 20 x 3 x 2 = 120 bytes), you store 1 pixel and some additional info that says 'repeat me 20 times' (maybe 6 bytes + 1 byte for the integer = 7 bytes).
    The image is completely preserved, but at a reduced filesize. The disadvantage of this is it takes longer to open because you need to recreate those pixels from instructions instead of just reading their values.
     
  13. ShunCheung

    ShunCheung Moderator

    On the D70 and D70s, and the up-coming D80, the RAW NEF files are always compressed. There is no option not to compress them.
     
  14. And, as many people has expained us, the NEF compression algorithm isn't completely losseless, it loses some highlights. However, for most of us it is practicaly unnoticeable.

    Ioritz.
     
  15. It is not 'how many megapixels are my pics?" or how many megabytes are my files, it is "did
    you get the shot"
     
  16. Robert,

    I'm not familiar with the internals on NEF (just with those of crw/cr2),
    but dont forget, that the camera might want a jpg to show in the display. This might be embedded into the NEF file. (And since its a jpg, its add some varying size to the filesize of the NEF). Besides that, from what I've heard, NEFs of the smaller Nikons are compressed (like mentioned above).

    Rainer
     
  17. Jim: LOL.. good one.


    all: very good info here! thank you for the replies!
     
  18. To clarify what Chad said, a RAW file (and almost every digital camera) only records one color per photo site. So it's 12 bits / pixel in a RAW file.

    Peter, not sure if you were saying this, but they don't pad 12 bit data with zeros to make it 16 bit, even for an uncompressed RAW. If you look at a D200 uncompressed RAW file, you'll see it's around 15.6 million bytes. 12 bits per photo site / 8 bits per byte = 1.5 bytes / photo site. Multiply that by 10 million photo sites, and you get 15 million bytes per RAW file. Plus there is a very low quality JPG written as a preview image...
     

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