Q on graphic size

Discussion in 'Digital Photography' started by satoshi, Jun 4, 2005.

  1. satoshi

    satoshi Guest

    During this memorial holiday vacation, I took tons of pictures with a new
    Sony DSC T1 digital camera (5MP).
    In order to save space, image size was set at 3MP (instead of 5MP). Then,
    images were downloaded to my computers. The images looked great to my
    naked eyes. When I looked at the files, all of them are in jpg format but
    the images sizes are 1.3MB to 1.4 MB. I expected them to be 5mb. I am
    wondering what is the conversion equation from MP to MB. Please enlighten
    me. TIA. Satoshi
     
    satoshi, Jun 4, 2005
    #1
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  2. "satoshi" <> writes:

    > During this memorial holiday vacation, I took tons of pictures with a new
    > Sony DSC T1 digital camera (5MP).


    > In order to save space, image size was set at 3MP (instead of 5MP).
    > Then, images were downloaded to my computers. The images looked
    > great to my naked eyes. When I looked at the files, all of them are
    > in jpg format but the images sizes are 1.3MB to 1.4 MB. I expected
    > them to be 5mb. I am wondering what is the conversion equation from
    > MP to MB. Please enlighten me.


    Pixels ain't bytes! That's why they have different names.

    In most images you will work with, each pixel is represented by
    *three* bytes, one giving the red light intensity, one giving the
    green light intensity, and one giving the blue light intensity.
    Uncompressed, a 3MP image would take up 3MB.

    JPEG compression is really *very* good at making still image files
    smaller. I guess those alleged "experts" really were! (JPEG stands
    for "Joint Photographic Experts Group").

    So that's how your 3MP images end up as 1.3MB or so files. The exact
    degree of compression depends on the JPEG settings used (your camera
    may well give you a couple of choices, often called things like
    "normal", "fine", or "super-fine") AND on the content of the image
    (hence the variation in size between images taken with the same
    settings).

    I have no idea how you managed to start out expecting the files to be
    5MB for 3MP images, by the way; I don't follow that bit. Not
    important, really.

    (I'm talking here about "24-bit color", which is what the vast
    majority of images floating around in the digital world are in I
    think. I'm avoiding other, more complicated, cases because they don't
    seem relevant to the original poster's question, not because I've
    never heard of them.)
    --
    David Dyer-Bennet, <mailto:>, <http://www.dd-b.net/dd-b/>
    RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/>
    Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAlbum/>
    Dragaera/Steven Brust: <http://dragaera.info/>
     
    David Dyer-Bennet, Jun 4, 2005
    #2
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  3. satoshi

    Tony Hwang Guest

    satoshi wrote:

    > During this memorial holiday vacation, I took tons of pictures with a new
    > Sony DSC T1 digital camera (5MP).
    > In order to save space, image size was set at 3MP (instead of 5MP). Then,
    > images were downloaded to my computers. The images looked great to my
    > naked eyes. When I looked at the files, all of them are in jpg format but
    > the images sizes are 1.3MB to 1.4 MB. I expected them to be 5mb. I am
    > wondering what is the conversion equation from MP to MB. Please enlighten
    > me. TIA. Satoshi
    >
    >

    Hi,
    Are you trolling? I am serious!
    Anatawa isi adama detsuka?
    Pixel and bytes are two different thing.
    Tony
     
    Tony Hwang, Jun 4, 2005
    #3
  4. satoshi

    Jim Townsend Guest

    satoshi wrote:

    Just to touch on David's excellent reply..

    All your 3 megapixel images are 9 megabytes in size. They have
    to be to hold the 3 color information David described.

    With JPEG, the images are COMPRESSED before they are saved
    to your memory card. JPEG uses a very efficient compression
    algorithm which results in very small file sizes.

    This scheme saves disk space and reduces transfer time over a
    network, or between devices like your camera and computer.

    When you open JPEG images and view them on your computer, they
    must be uncompressed back to the required 9 megabytes by whatever
    software you are using to view the image. They exist as 1.4MB
    files on your hard disk, but get inflated back to 9 megabytes when
    they are transferred to your computer memory.
     
    Jim Townsend, Jun 4, 2005
    #4
  5. satoshi

    Paul Furman Guest

    satoshi wrote:
    > During this memorial holiday vacation, I took tons of pictures with a new
    > Sony DSC T1 digital camera (5MP).
    > In order to save space, image size was set at 3MP (instead of 5MP). Then,
    > images were downloaded to my computers. The images looked great to my
    > naked eyes. When I looked at the files, all of them are in jpg format but
    > the images sizes are 1.3MB to 1.4 MB. I expected them to be 5mb. I am
    > wondering what is the conversion equation from MP to MB. Please enlighten
    > me. TIA. Satoshi


    There is no conversion btwn MP & MB with jpegs. Jpeg file sizes can vary
    depending on compression. Mexapixels (MP) is simply the number of pixels.
     
    Paul Furman, Jun 4, 2005
    #5
  6. Jim Townsend <> writes:

    > satoshi wrote:
    >
    > Just to touch on David's excellent reply..
    >
    > All your 3 megapixel images are 9 megabytes in size. They have
    > to be to hold the 3 color information David described.


    I somehow typed the wrong number in my message. AAIIIIEEEEEE! I
    remember so clearly thinking the right thing, and I never noticed
    before sending it off. Anyone know a good shop to do a CLA on a
    slightly used brain?
    --
    David Dyer-Bennet, <mailto:>, <http://www.dd-b.net/dd-b/>
    RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/>
    Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAlbum/>
    Dragaera/Steven Brust: <http://dragaera.info/>
     
    David Dyer-Bennet, Jun 4, 2005
    #6
  7. satoshi

    Paul Furman Guest

    David Dyer-Bennet wrote:

    > "satoshi" <> writes:
    >
    >> I am wondering what is the conversion equation from
    >> MP to MB. Please enlighten me.

    >
    >
    > Pixels ain't bytes!



    Thanks for that clear statement <g>.
     
    Paul Furman, Jun 4, 2005
    #7
  8. satoshi

    Ron Hunter Guest

    satoshi wrote:
    > During this memorial holiday vacation, I took tons of pictures with a new
    > Sony DSC T1 digital camera (5MP).
    > In order to save space, image size was set at 3MP (instead of 5MP). Then,
    > images were downloaded to my computers. The images looked great to my
    > naked eyes. When I looked at the files, all of them are in jpg format but
    > the images sizes are 1.3MB to 1.4 MB. I expected them to be 5mb. I am
    > wondering what is the conversion equation from MP to MB. Please enlighten
    > me. TIA. Satoshi
    >
    >

    The unprocessed size of a 3mp picture is 9 megabytes. Cameras that
    output .jpg files always compress the data to save space on the flash
    cards. The compression varies from picture to picture, but usually runs
    somewhere close to 10:1, so your pictures are well within the range of
    most cameras as to compression.

    The camera captures 24 bits (3 bytes) of data for each pixel, so
    multiply the 'mp' size by 3 for the 'raw' size of the image. Then .jpg
    compression is applied to the data.


    --
    Ron Hunter
     
    Ron Hunter, Jun 4, 2005
    #8
  9. satoshi

    Ron Hunter Guest

    David Dyer-Bennet wrote:
    > "satoshi" <> writes:
    >
    >
    >>During this memorial holiday vacation, I took tons of pictures with a new
    >>Sony DSC T1 digital camera (5MP).

    >
    >
    >>In order to save space, image size was set at 3MP (instead of 5MP).
    >>Then, images were downloaded to my computers. The images looked
    >>great to my naked eyes. When I looked at the files, all of them are
    >>in jpg format but the images sizes are 1.3MB to 1.4 MB. I expected
    >>them to be 5mb. I am wondering what is the conversion equation from
    >>MP to MB. Please enlighten me.

    >
    >
    > Pixels ain't bytes! That's why they have different names.
    >
    > In most images you will work with, each pixel is represented by
    > *three* bytes, one giving the red light intensity, one giving the
    > green light intensity, and one giving the blue light intensity.
    > Uncompressed, a 3MP image would take up 3MB.


    No. 9MB!


    >
    > JPEG compression is really *very* good at making still image files
    > smaller. I guess those alleged "experts" really were! (JPEG stands
    > for "Joint Photographic Experts Group").
    >
    > So that's how your 3MP images end up as 1.3MB or so files. The exact
    > degree of compression depends on the JPEG settings used (your camera
    > may well give you a couple of choices, often called things like
    > "normal", "fine", or "super-fine") AND on the content of the image
    > (hence the variation in size between images taken with the same
    > settings).
    >
    > I have no idea how you managed to start out expecting the files to be
    > 5MB for 3MP images, by the way; I don't follow that bit. Not
    > important, really.
    >
    > (I'm talking here about "24-bit color", which is what the vast
    > majority of images floating around in the digital world are in I
    > think. I'm avoiding other, more complicated, cases because they don't
    > seem relevant to the original poster's question, not because I've
    > never heard of them.)



    --
    Ron Hunter
     
    Ron Hunter, Jun 4, 2005
    #9
  10. satoshi

    Ron Hunter Guest

    David Dyer-Bennet wrote:
    > Jim Townsend <> writes:
    >
    >
    >>satoshi wrote:
    >>
    >>Just to touch on David's excellent reply..
    >>
    >>All your 3 megapixel images are 9 megabytes in size. They have
    >>to be to hold the 3 color information David described.

    >
    >
    > I somehow typed the wrong number in my message. AAIIIIEEEEEE! I
    > remember so clearly thinking the right thing, and I never noticed
    > before sending it off. Anyone know a good shop to do a CLA on a
    > slightly used brain?


    Slightly used? Sigh. At my age, 'slightly' isn't the accurate term. I
    was sure, given the accuracy of the rest of your response that you
    were suffering from a common newsgroup problem, fast brain, slow
    fingers.... Grin.


    --
    Ron Hunter
     
    Ron Hunter, Jun 4, 2005
    #10
  11. satoshi

    satoshi Guest

    Thanks for excellent posts from you and others.

    >I have no idea how you managed to start out expecting the files to be
    >5MB for 3MP


    5MB was a typo. In fact, I was not thinking 3b for 1 px for color.
    Sometime, brain cells do not work properly.

    Thanks again. Satoshi






    "David Dyer-Bennet" <> wrote in message
    news:-b.net...
    > "satoshi" <> writes:
    >
    >> During this memorial holiday vacation, I took tons of pictures with a new
    >> Sony DSC T1 digital camera (5MP).

    >
    >> In order to save space, image size was set at 3MP (instead of 5MP).
    >> Then, images were downloaded to my computers. The images looked
    >> great to my naked eyes. When I looked at the files, all of them are
    >> in jpg format but the images sizes are 1.3MB to 1.4 MB. I expected
    >> them to be 5mb. I am wondering what is the conversion equation from
    >> MP to MB. Please enlighten me.

    >
    > Pixels ain't bytes! That's why they have different names.
    >
    > In most images you will work with, each pixel is represented by
    > *three* bytes, one giving the red light intensity, one giving the
    > green light intensity, and one giving the blue light intensity.
    > Uncompressed, a 3MP image would take up 3MB.
    >
    > JPEG compression is really *very* good at making still image files
    > smaller. I guess those alleged "experts" really were! (JPEG stands
    > for "Joint Photographic Experts Group").
    >
    > So that's how your 3MP images end up as 1.3MB or so files. The exact
    > degree of compression depends on the JPEG settings used (your camera
    > may well give you a couple of choices, often called things like
    > "normal", "fine", or "super-fine") AND on the content of the image
    > (hence the variation in size between images taken with the same
    > settings).
    >
    > I have no idea how you managed to start out expecting the files to be
    > 5MB for 3MP images, by the way; I don't follow that bit. Not
    > important, really.
    >
    > (I'm talking here about "24-bit color", which is what the vast
    > majority of images floating around in the digital world are in I
    > think. I'm avoiding other, more complicated, cases because they don't
    > seem relevant to the original poster's question, not because I've
    > never heard of them.)
    > --
    > David Dyer-Bennet, <mailto:>, <http://www.dd-b.net/dd-b/>
    > RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/>
    > Pics: <http://dd-b.lighthunters.net/>
    > <http://www.dd-b.net/dd-b/SnapshotAlbum/>
    > Dragaera/Steven Brust: <http://dragaera.info/>
     
    satoshi, Jun 4, 2005
    #11
  12. "satoshi" <> writes:

    > Thanks for excellent posts from you and others.
    >
    >>I have no idea how you managed to start out expecting the files to be
    >>5MB for 3MP

    >
    > 5MB was a typo. In fact, I was not thinking 3b for 1 px for color.
    > Sometime, brain cells do not work properly.


    Tell me about it; you've seen by now that *I* managed to mess up the
    size numbers while correcting you on them!
    --
    David Dyer-Bennet, <mailto:>, <http://www.dd-b.net/dd-b/>
    RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/>
    Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAlbum/>
    Dragaera/Steven Brust: <http://dragaera.info/>
     
    David Dyer-Bennet, Jun 4, 2005
    #12
  13. satoshi

    satoshi Guest

    David,

    In comparison to conventional film cameras, I feel the steep learning curve
    for beginners using digital cameras. I still could not digest the whole
    manual. RAM in my head was not big enough to hold all howtos. I wish that
    I could implant a 1GB RAM to my brain. Pictures were taken with Sony T1
    (5MP) in Sedona, Arizona during the past memorial holiday. That was my
    first exposure to digital camera. In order to save memory space in memory
    stick, I set the picture size to 3mp. When downloaded, all of them were in
    1.1-1.3 MB size. I was worried about the quality of prints. That worry
    triggered me to post the question to this NG.

    Pictures were printed at Costco at a cost of 17c/print (3 x 5). All
    pictures were turned out to be sharp and gorgeous. To my naked eyes, I do
    not see any difference between digital and film prints. I am now a
    satisfied customer with Sony Camera. Good bye to my Pentax and Olympus
    film cameras. Satoshi









    "David Dyer-Bennet" <> wrote in message
    news:-b.net...
    > "satoshi" <> writes:
    >
    >> Thanks for excellent posts from you and others.
    >>
    >>>I have no idea how you managed to start out expecting the files to be
    >>>5MB for 3MP

    >>
    >> 5MB was a typo. In fact, I was not thinking 3b for 1 px for color.
    >> Sometime, brain cells do not work properly.

    >
    > Tell me about it; you've seen by now that *I* managed to mess up the
    > size numbers while correcting you on them!
    > --
    > David Dyer-Bennet, <mailto:>, <http://www.dd-b.net/dd-b/>
    > RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/>
    > Pics: <http://dd-b.lighthunters.net/>
    > <http://www.dd-b.net/dd-b/SnapshotAlbum/>
    > Dragaera/Steven Brust: <http://dragaera.info/>
     
    satoshi, Jun 5, 2005
    #13
  14. "satoshi" <> writes:

    > In comparison to conventional film cameras, I feel the steep
    > learning curve for beginners using digital cameras.


    I can easily believe it. I came to digital photography only after 30
    years of film photography (including medium and large format as well
    as 35mm, and doing my own darkroom work a lot) and 30 years of
    computer programming; and before I started actual digital
    *photography*, I'd been working with scanned images (and later
    scanning my own film) for 5 or so years. I had a big head start on
    the learning curve, and I took it really slow. And I'm sure there are
    a number of features of my current camera I'm still not using
    optimally!

    > I still could not digest the whole manual. RAM in my head was not
    > big enough to hold all howtos. I wish that I could implant a 1GB
    > RAM to my brain. Pictures were taken with Sony T1 (5MP) in Sedona,
    > Arizona during the past memorial holiday. That was my first
    > exposure to digital camera. In order to save memory space in memory
    > stick, I set the picture size to 3mp. When downloaded, all of them
    > were in 1.1-1.3 MB size. I was worried about the quality of prints.
    > That worry triggered me to post the question to this NG.


    I hope I didn't give the impression I thought you were "dumb". A bit
    confused, yes, but then you already knew that, it's what prompted you
    to ask the question in the first place. Ignorance is curable, and
    there's nothing shameful about it.

    > Pictures were printed at Costco at a cost of 17c/print (3 x 5). All
    > pictures were turned out to be sharp and gorgeous. To my naked eyes, I do
    > not see any difference between digital and film prints. I am now a
    > satisfied customer with Sony Camera. Good bye to my Pentax and Olympus
    > film cameras. Satoshi


    Good, glad that worked out. It *should* have worked out, 3MP is fine
    for that small print size. It's nice when practice works as predicted
    in theory!
    --
    David Dyer-Bennet, <mailto:>, <http://www.dd-b.net/dd-b/>
    RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/>
    Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAlbum/>
    Dragaera/Steven Brust: <http://dragaera.info/>
     
    David Dyer-Bennet, Jun 5, 2005
    #14
  15. satoshi

    satoshi Guest

    In fact, I was pleasantry surprised to see such nice prints. I could not
    believe those prints. I read tons of comments saying that digital prints
    won't match film prints. That's what I was concerned. For amateurs, they
    won't likely for 8 x 10 prints unless those have to do with very important
    events. This first exposure of digital camera tells me that 3-5 mp camera
    would make everybody happy. I just learned that New Canon Eos 20Da will
    have "LCD preview" :
    http://www.steves-digicams.com/pr/canon_06022005_20da_pr.html. I might
    consider to upgrade to this dSLR by the end of this year. Thanks for the
    wonderful and practical information on digital image from this NG. I thank
    to David for your kind understanding. Satoshi



    "David Dyer-Bennet" <> wrote in message
    news:-b.net...
    > "satoshi" <> writes:
    >
    >> In comparison to conventional film cameras, I feel the steep
    >> learning curve for beginners using digital cameras.

    >
    > I can easily believe it. I came to digital photography only after 30
    > years of film photography (including medium and large format as well
    > as 35mm, and doing my own darkroom work a lot) and 30 years of
    > computer programming; and before I started actual digital
    > *photography*, I'd been working with scanned images (and later
    > scanning my own film) for 5 or so years. I had a big head start on
    > the learning curve, and I took it really slow. And I'm sure there are
    > a number of features of my current camera I'm still not using
    > optimally!
    >
    >> I still could not digest the whole manual. RAM in my head was not
    >> big enough to hold all howtos. I wish that I could implant a 1GB
    >> RAM to my brain. Pictures were taken with Sony T1 (5MP) in Sedona,
    >> Arizona during the past memorial holiday. That was my first
    >> exposure to digital camera. In order to save memory space in memory
    >> stick, I set the picture size to 3mp. When downloaded, all of them
    >> were in 1.1-1.3 MB size. I was worried about the quality of prints.
    >> That worry triggered me to post the question to this NG.

    >
    > I hope I didn't give the impression I thought you were "dumb". A bit
    > confused, yes, but then you already knew that, it's what prompted you
    > to ask the question in the first place. Ignorance is curable, and
    > there's nothing shameful about it.
    >
    >> Pictures were printed at Costco at a cost of 17c/print (3 x 5). All
    >> pictures were turned out to be sharp and gorgeous. To my naked eyes, I
    >> do
    >> not see any difference between digital and film prints. I am now a
    >> satisfied customer with Sony Camera. Good bye to my Pentax and Olympus
    >> film cameras. Satoshi

    >
    > Good, glad that worked out. It *should* have worked out, 3MP is fine
    > for that small print size. It's nice when practice works as predicted
    > in theory!
    > --
    > David Dyer-Bennet, <mailto:>, <http://www.dd-b.net/dd-b/>
    > RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/>
    > Pics: <http://dd-b.lighthunters.net/>
    > <http://www.dd-b.net/dd-b/SnapshotAlbum/>
    > Dragaera/Steven Brust: <http://dragaera.info/>
     
    satoshi, Jun 5, 2005
    #15
  16. satoshi <> wrote:
    : In fact, I was pleasantry surprised to see such nice prints. I could
    : not believe those prints. I read tons of comments saying that digital
    : prints won't match film prints. That's what I was concerned. For
    : amateurs, they won't likely for 8 x 10 prints unless those have to do
    : with very important events. This first exposure of digital camera
    : tells me that 3-5 mp camera would make everybody happy.

    a 3mp image should be able to be printed up to 8x10 with acceptable
    results. If you are primarily interrested in 3x5s your 3mp images should
    be great. And you will even have a little "breathing room" if you decide
    to crop the image a bit. If you think that you may want to crop and then
    print to 8x10 you may want to bump the camera back up to 5mp so you keep
    that breathing room. :)

    Randy

    ==========
    Randy Berbaum
    Champaign, IL
     
    Randy Berbaum, Jun 5, 2005
    #16
  17. satoshi

    satoshi Guest

    Randy, I reset the camera to 5mp size.
    I now have 500 mb memory stick.

    Let me ask you this question: What format does Costco or other companies
    (e.g., ofoto) accept for printing?
    What I meant was whether they take cdr, tiff, pdf (converted to pdf with
    Photoshop), psd (photoshop format) or other formats to print. If they
    could take pdf, it would be great. Satoshi





    "Randy Berbaum" <> wrote in message
    news:d7tsok$ava$...
    > satoshi <> wrote:
    > : In fact, I was pleasantry surprised to see such nice prints. I could
    > : not believe those prints. I read tons of comments saying that digital
    > : prints won't match film prints. That's what I was concerned. For
    > : amateurs, they won't likely for 8 x 10 prints unless those have to do
    > : with very important events. This first exposure of digital camera
    > : tells me that 3-5 mp camera would make everybody happy.
    >
    > a 3mp image should be able to be printed up to 8x10 with acceptable
    > results. If you are primarily interrested in 3x5s your 3mp images should
    > be great. And you will even have a little "breathing room" if you decide
    > to crop the image a bit. If you think that you may want to crop and then
    > print to 8x10 you may want to bump the camera back up to 5mp so you keep
    > that breathing room. :)
    >
    > Randy
    >
    > ==========
    > Randy Berbaum
    > Champaign, IL
    >
     
    satoshi, Jun 5, 2005
    #17
  18. satoshi <> wrote:
    : Randy, I reset the camera to 5mp size.
    : I now have 500 mb memory stick.

    : Let me ask you this question: What format does Costco or other companies
    : (e.g., ofoto) accept for printing?
    : What I meant was whether they take cdr, tiff, pdf (converted to pdf with
    : Photoshop), psd (photoshop format) or other formats to print. If they
    : could take pdf, it would be great. Satoshi

    Since I have never used any of these locations I don't know the price they
    charge. I do all my own printing at home. But from what I have taken from
    similar discussions I think most places prefer JPG files but some
    locations use machinery that can take other file formats. Your best bet
    would be to phone your local store and ask the folks at the photography
    desk what formats their equipment can handle. It is possible that some of
    them may be able to use a Photoshop format, but this would probably be
    fewer than other more prevalent formats (Adobe tends to be protective of
    their in-house formats). But if you convert one of these files to a low
    compression (12) JPG just for transport to the photo shop for printing you
    should do just fine. Remember that if you have multiple layers on a PS
    formated photo, you will have to "flatten" it before you can "save as" a
    JPG file.

    Randy

    ==========
    Randy Berbaum
    Champaign, IL
     
    Randy Berbaum, Jun 6, 2005
    #18
  19. satoshi

    Marvin Guest

    satoshi wrote:
    > During this memorial holiday vacation, I took tons of pictures with a new
    > Sony DSC T1 digital camera (5MP).
    > In order to save space, image size was set at 3MP (instead of 5MP). Then,
    > images were downloaded to my computers. The images looked great to my
    > naked eyes. When I looked at the files, all of them are in jpg format but
    > the images sizes are 1.3MB to 1.4 MB. I expected them to be 5mb. I am
    > wondering what is the conversion equation from MP to MB. Please enlighten
    > me. TIA. Satoshi
    >
    >

    The size of a .jpg file depends on the compression factor, and on details of the picture.
    I set the compression factor for my 3 Mp camera by experimenting with the
    compressions available, and I settled on one that gives files of about 2/3 Mp. You
    either have a minimal compression factor, or your photos may be 5 Mp. Perhaps your camera
    didn't maintain the 3 Mp setting you made.
     
    Marvin, Jun 6, 2005
    #19
  20. satoshi

    Guest

    On Fri, 03 Jun 2005 21:56:06 -0500, David Dyer-Bennet <>
    wrote:

    >"satoshi" <> writes:
    >
    >> During this memorial holiday vacation, I took tons of pictures with a new
    >> Sony DSC T1 digital camera (5MP).

    >
    >> In order to save space, image size was set at 3MP (instead of 5MP).
    >> Then, images were downloaded to my computers. The images looked
    >> great to my naked eyes. When I looked at the files, all of them are
    >> in jpg format but the images sizes are 1.3MB to 1.4 MB. I expected
    >> them to be 5mb. I am wondering what is the conversion equation from
    >> MP to MB. Please enlighten me.

    >
    >Pixels ain't bytes! That's why they have different names.
    >
    >In most images you will work with, each pixel is represented by
    >*three* bytes, one giving the red light intensity, one giving the
    >green light intensity, and one giving the blue light intensity.
    >Uncompressed, a 3MP image would take up 3MB.
    >
    >JPEG compression is really *very* good at making still image files
    >smaller. I guess those alleged "experts" really were! (JPEG stands
    >for "Joint Photographic Experts Group").
    >
    >So that's how your 3MP images end up as 1.3MB or so files. The exact
    >degree of compression depends on the JPEG settings used (your camera
    >may well give you a couple of choices, often called things like
    >"normal", "fine", or "super-fine") AND on the content of the image
    >(hence the variation in size between images taken with the same
    >settings).
    >
    >I have no idea how you managed to start out expecting the files to be
    >5MB for 3MP images, by the way; I don't follow that bit. Not
    >important, really.


    Maybe because of the logic implied in your statement above,
    "In most images you will work with, each pixel is represented by
    *three* bytes, one giving the red light intensity, one giving the
    green light intensity, and one giving the blue light intensity", which
    would get you to 9MB for openers, not, as you further said,
    "Uncompressed, a 3MP image would take up 3MB."

    >
    >(I'm talking here about "24-bit color", which is what the vast
    >majority of images floating around in the digital world are in I
    >think. I'm avoiding other, more complicated, cases because they don't
    >seem relevant to the original poster's question, not because I've
    >never heard of them.)
     
    , Jun 7, 2005
    #20
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