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Quality v Size of Digital photos

Discussion in 'Photography Forums' started by Daverey2, Nov 30, 2004.

  1. Daverey2

    Daverey2
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    Hi
    I've just returned form my first holiday using my new digital camera, and have a question about the quality of the photos taken when loaded onto the PC.

    My camera is a Pentax Optio S40, and I took phootos on medium quality and medium size - perfectly adequate for what I wanted.

    When I copied the files across to my PC, each one was approximately 600kb in size.

    However, when I opened the pictures in my viewing software (something called XNView I think) and then saved them (still as JPEGs), the file size had reduced to aroun 250kb each.

    Probably a daft question I know, but has this decrease in file size been due to a decrease in quality of the picture, or does the PC compress the sizes more effectively. I am worried that if I only reatin the smaller sized photos, if I want any printing in the future they will not be as good?

    Thanks in adavance

    Dave
     
  2. Mango Bob

    Mango Bob
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    Sounds like XNView has saved the files and recompressed them - so you've lost quality. It's not immediately obvious where you've lost picture detail, but your files have halved in size so you've definitely lost information.

    Make sure you keep the original or copy them back off the camera. The difference may not be obvious on screen but may show up if you print the pics.

    Generally unless you're short of memory you're best off shooting everything at highest quality and resolution. Newer cameras (possibly the Optio included) will allow you to recompress pictures to lower quality if you start to run low on memory. At lower quality you can never blow up that perfect shot you took to A3 size. You can always make the files smaller/copy them to disc in an internet cafe but you can never add information that's not there.
     
  3. Daverey2

    Daverey2
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    Thanks for that - thought as much.

    Dave
     
  4. Geordie Jester

    Geordie Jester
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    Yep. Just to back up what Mango said, sounds like they have been recompressed. This is one thing to always be careful of. One thing I like to do is to take them off the camera and save them as TIFF files (or something non-compressing). This will mean the files are pretty big, but you can then manipulate as you like and only ever save to a JPG if you need to compress them for say an email. The worst case scenario is that you open a pic, change its brightness, save, reopen, change a bit of background, save, reopen, crop, save. All the saves can result in compressing the compressed image, degrading it more and more each time you save. Using a TIFF or BMP stops this.

    As Mango said, if they are saved as JPG on the camera you have already lost image detail as they have been internally compressed. Best to use a RAW or TIFF format if possible.

    It all comes down to practicality and cost at the end of the day. When I was on holiday I set camera to High Quality JPG to be able to get 150-200 shots on card. But if I was going to shoot something for a day I would go to TIFF and only be able to store 20 shots, but at much better quality.
     
  5. martynk

    martynk
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    I agree. You've got some choices here, depending on what the camera will allow (I don't know the Optio), and I'd experiment with various resolutions and formats to see what combination gives the results I need/want in print. For example, I shoot all my work images - loss adjusting - at 1600 x 1200 Hi Quality JPEG, which gives about 100 on a 128MB card, but these are going to be emailed, or printed at postcard size. I could probably drop to Standard or even Economy JPEG, but the Hi Quality gives a bit of flexibility for cropping/zooming. These images aren't edited very much - only quick fix stuff - because my clients just want sharp, clear, photographs and aren't very interested in creative or artistic efforts! I use 2560 x 1920 for personal photography, either Hi Quality JPEG or TIFF. It doesn't seem to make a great deal of difference, but I save everything as a TIFF or PSD file.
     
  6. HotblackDesiato

    HotblackDesiato
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    If you're resaving in jpeg you may find there are resolution options (within the save window) that will allow you to reduce the recompression effect you're seeing.
    I use maximum resolution, RAW and only convert to Tiff if there's something i want to print. The downside is you can only squeeze 100-120 shots onto a 1GB card and the Tiffs run to 50MB.
     

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