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size = quality

Discussion in 'Digital Photography & Imaging' started by BigDadBuddha, Nov 28, 2004.

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  1. BigDadBuddha

    BigDadBuddha Thread Starter

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    I have a 5 megapixel camera .
    Each pic(jpeg) is approx 2 megs.
    I mostly will be printing 4x6 or 5x7 ( Ocassionally8x10).
    Do I have to keep camera at 5 megapixel or would 3 megapixel setting work fine? Also,after editing pictures with other software , when I save them they are approx 1/4 to 1/2 the size (from 2 megs down to 500kb). Will I lose quality this way when I print? I cant understand how the size can be so much smaller.....Anyone????
     
  2. kiwiguy

    kiwiguy

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    JPG is a compressed file system.

    When you alter a file, save it in a non compressed file format first (such as BMP) or each time you save it there will be more compression added, and more quality lost (hence the smaller file size).

    Once the changes are complete you could save it in JPG and delete the large BMP one.

    I find 3 MP adequate for printing 6x4, but would retain the 5 MP for 8x10 (but you would probably find that 3 MP would give reasonable results). Simplest answer is to try it and see, then you can make the judgement with your gear and your eyes.
     
  3. BigDadBuddha

    BigDadBuddha Thread Starter

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    So, when i edit a pic (sometimes, all I do is rotate it), and it goes from 2 megs to 500kb ,I am losing alot of quality in a 4x6?
     
  4. alanmzifa

    alanmzifa

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    Nov 30, 2003
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    yes ,
    i'm sure you have some software installed on your computer that came with your camera for basic picture editing ( and probably manages picure downloads from the camera too )
    in the tools or options or preferences menu you'll probably find some settings which you can adjust for the default compression ratio used .

    one of these is usually lossless jpeg compression ( which means a 2mb pic will be saved as a 2mb pic ) .
     
  5. slipe

    slipe

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    Your camera has both quality and image size settings. The quality setting determines how much the camera will compress the image – the less compression the better the quality.

    My personal feeling is that those photos are your lifetime memories and you should take them at the highest quality the camera will give. You never know when you will take a picture you want on the wall or have to crop severely to get a small part. Or when you will get interested in graphics and buy a wide format photo printer etc. Of course if your memory card is too small it might be a better choice than running out of space and missing shots altogether.

    If you absolutely have to reduce the file size I would go one notch down in quality before lowering the resolution.

    There is no such thing as loseless JPG. A 5Mp file reduced to 2 Mb is decent quality but there is some loss. If you work on an image and save it again as a 2 Mb JPG file you have compounded the original compression artifacts by re-compressing the image. You should “Save As” in an uncompressed file type – TIFF is the most common. Your 5Mp image will be 14.4 Mb in an uncompressed TIFF to give you an idea how much compression 2 Mb is for a 5Mp file. Always save the original that came from the camera – hence ”Save As” rather than “Save”.

    Your choice of compression varies with programs. I just saved a 5Mp image at best quality in both Irfanview (quality 100) and Photoshop (quality 12). The Photoshop file was about 3.5 Mb and the Irfanview file about 2.8 Mb, so Photoshop has a little higher best quality. The quality to end up with 2Mp isn’t bad – you would be hard pressed to see the difference unless you re-saved a couple of times as JPG.

    500k is relatively poor quality for a 5Mp image. No big deal as long as you used “Save as” rather than “Save”. You still have the original that way if you ever want a larger print. There is no reason to “Save as” JPG unless you are hard pressed for space or intend to post or e-mail the image. People generally reduce both the size and quality some to post or send by e-mail. After you have worked on an image save it in an uncompressed format if you ever intend using it yourself. You can then also save a compressed copy for mailing etc. If you just need to rotate some files use something like Irfanview which will do a loseless rotation for you.

    This is the save dialog from Irfanview. The slider labeled “Save quality” determines how large the file will end up.
    [​IMG]
     
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