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Thread: New member - Query re sensors and file size chosen

  1. #1
    New Member
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    Pedro

    New member - Query re sensors and file size chosen

    Hi everone, Pedro here , just found your group by accident while searching for info, such as : Assuming that whatever size photo is selected in the menu , L, M, or S the lens will still use the whole sensor area ? Does that mean that by selecting Small size photo the pixels at sensor level will be much larger ? That is cramming 16mp onto the same size sensor will be smaller pixels than electing the 12mp size ? I find this particular issue a little confusing, maybe I'm thick LOL ...
    Last edited by Donald; 20th February 2012 at 05:04 PM.

  2. #2
    Moderator Donald's Avatar
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    Just add 'MacKenzie'

    Re: New member - Query re sensors and file size chosen

    Pedro - as advised in the 'New member' thread, I have copied your first post into this new thread so that more members are likely to see your question and be able to help.

  3. #3
    herbert's Avatar
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    Re: New member - Query re sensors and file size chosen

    Hi Pedro,

    The smaller file sizes are achieved using downsizing of the image and JPEG compression.

    Downsizing is like combining pixels. All the image pixels are used to create a smaller image. This is done by interpolation. A series of neighbour pixels can be used to create a line showing how the intensity of the image is changing. Any point on the line can now be sampled. This allows you to generate an image with whatever number of pixels you like. If you choose to sample less than the original you will reduce the size. You can choose to sample more than the original. This will enlarge your image.

    JPEG compression reduces the file size by mapping the original pixel colours to a set of colours than represents the whole image. So each pixel gets a new colour. If you have a massive table then you can specify all the colours in the original image. No compression. If you reduce the size of the table then you have to change some colours (this is done to the least common colours first). But you can save storage space. If you reduce the number of colours too far then you will see obvious banding in the image as adjacent colours are so different the eye can easily see the change.

    Not all the original colours are in the JPEG compressed version; this is called lossy compression since you have discarded some information. However it is often possible to reduce the file size by ten-fold without the eye being able to see the difference.

    On your camera each L, M and S will have a number of pixels. You may also be able to set either fine or coarse file types. L, M and S effect the interpolation sampling interval (and so the final pixel dimensions). Fine/Coarse sets the number of colours you wish to sub-sample using the JPEG compression.

    In image editing software you also get the chance to set the JPEG compression amount when saving your files. This may be on a scale of 1-10 or 0-100%. A setting of 80% will be a good starting point for nice looking images.

    Beware that each time you open a JPEG, edit it, re-save and then close the image the compression will have reduced the quality of the image. This only applies each time you close the image in the software. This is because it has the current pixels in memory and so works the JPEG compression on the full set of pixel colours each time you save. Opening, editing and saving the same photo many times and the image will be much worse. This is why it is a good idea to save your JPEGs using different file names or to keep the originals in a separate location.

    Hope this helps,

    Alex
    Last edited by herbert; 20th February 2012 at 06:04 PM.

  4. #4
    New Member
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    Re: New member - Query re sensors and file size chosen

    Thank you Alex , a good clear explanation. I am most grateful , Pedro

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