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Author Topic: sharpness - is it just too compressed in jpeg?  (Read 2850 times)

acellier

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sharpness - is it just too compressed in jpeg?
« on: August 04, 2013, 07:00:42 PM »

    Conventional wisdom about image sharpness on this board has been limited depth of focus
    Too bad we can't select a higher jpg quality, level to see if this is true ...
    When looking closely for detail in ftp'd images of vehicles, people, whatever - I'm seeing effects of compression, and concluding that the jpegs of only about 45 kilobytes is just too small for the 640x480 image. That's only 0.14 bytes per pixel, for full color!
    But for comparison, ten years back our first digital camera did 1280x960 and produced reasonably sharp looking 500 kB image. Each of those photos had four 640x480 subsets at 125 kB each - about 3 times as many bits as these D-link cameras are giving.
    My current digital camera does 4000x3000, making 5200 kB; dividing by 39 gives 133 kB - again, about 3 times as many bits per pixel.
    Can we add (choice of) higher jpg quality to the firmware wishlist for all these DCS-9xx cameras?
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acellier

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Re: sharpness - is it just too compressed in jpeg?
« Reply #1 on: August 07, 2013, 03:30:22 PM »

In case you wondered ...

from https://en.wikipedia.org/wiki/JPEG :
about 2/3 down the page ...
Sample photographs
... uncompressed 24-bit RGB bitmap image (313234 = 219726 pixels) requires 220kB
                                                            >>> so (640x480 = 307200 pixels) requires 921kB
... highest quality images ... about 8.25 bits per color pixel is required. 
                                                            >>> so (640x480 = 307200 pixels) requires 317kB
... medium quality image ... uses 1 bit per color pixel.
                                                            >>> so (640x480 = 307200 pixels) requires 38kB
... quality factor should not go below 0.75 bit per pixel
                                                            >>> at (640x480) that's 29kB

    Our recent experience ranges 29kB to 57kB. Thus, the DCS-93xL cameras appear to be at "medium quality" compression. So maybe lens focus *is* also part of the issue?
    Here is a comparison of a DCS-930L jpg and some good camera jpgs cropped and adjusted to the same pixel size and file size; also, the "good camera" shot was sized for same size at the license plate (35x20 pixels). - http://smg.photobucket.com/user/acellier/library/640x480%20jpg
    We can (just) read the license plate on the good camera shot, but not on the DCS-930L pic.
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RYAT3

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Re: sharpness - is it just too compressed in jpeg?
« Reply #2 on: August 07, 2013, 04:22:10 PM »

In case you wondered ...

from https://en.wikipedia.org/wiki/JPEG :
about 2/3 down the page ...
Sample photographs
... uncompressed 24-bit RGB bitmap image (313234 = 219726 pixels) requires 220kB
                                                            >>> so (640x480 = 307200 pixels) requires 921kB
... highest quality images ... about 8.25 bits per color pixel is required. 
                                                            >>> so (640x480 = 307200 pixels) requires 317kB
... medium quality image ... uses 1 bit per color pixel.
                                                            >>> so (640x480 = 307200 pixels) requires 38kB
... quality factor should not go below 0.75 bit per pixel
                                                            >>> at (640x480) that's 29kB

    Our recent experience ranges 29kB to 57kB. Thus, the DCS-93xL cameras appear to be at "medium quality" compression. So maybe lens focus *is* also part of the issue?
    Here is a comparison of a DCS-930L jpg and some good camera jpgs cropped and adjusted to the same pixel size and file size; also, the "good camera" shot was sized for same size at the license plate (35x20 pixels). - http://smg.photobucket.com/user/acellier/library/640x480%20jpg
    We can (just) read the license plate on the good camera shot, but not on the DCS-930L pic.


The DCS 2230 has the same kind of compression, so it's meant for speed, not quality.
101kb to 124kb for 2 megapixel camera

But it would be nice to switch it around and change the compression level.
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Notworried

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Re: sharpness - is it just too compressed in jpeg?
« Reply #3 on: August 08, 2013, 08:23:42 PM »

It is not compression. DCS-930L produces crappy pictures. Period. I have a discontinued DCS-920 that looks like HD in comparison.
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