Newbie: Canon A75 - Some Images look worse on higher res than lower

Discussion in 'Digital Photography' started by Mark, May 13, 2004.

  1. Mark

    Mark Guest

    I have been playing with this camera and some pics at 1600x1200 norm look worse or the same as 640x480 normal while others clearly look better at the 1600x1200 res. What I mean by worse is that they look abit more grainy and not as good resolution as if they were taken at 1mega pixel or lower. I am comparing daylight shots with other daylight shots and the results are not consistent.

    Thanks
     
    Mark, May 13, 2004
    #1
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  2. Mark

    Mark Guest

    I posted the pics in question for "expert" review:

    http://www3.telus.net/public/tmajer_/images/IMG_0036.jpg

    http://www3.telus.net/public/tmajer_/images/IMG_0064.JPG

    (the bad one)
    http://www3.telus.net/public/tmajer_/images/camera pic_sample.htm

    Mark



    I have been playing with this camera and some pics at 1600x1200 norm look worse or the same as 640x480 normal while others clearly look better at the 1600x1200 res. What I mean by worse is that they look abit more grainy and not as good resolution as if they were taken at 1mega pixel or lower. I am comparing daylight shots with other daylight shots and the results are not consistent.

    Thanks
     
    Mark, May 13, 2004
    #2
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  3. Is this occurring when you view the images at 100% on your monitor,
    or small enough to fit the entire image onscreen?

    If the latter, I suspect you're running afoul of 'aliasing'. You have
    a fixed number of pixels in a photo, and a fixed number displayed on your
    monitor. If the image is displayed in a res not evenly divisible by the
    monitor res, the display is fudged to account for trying to make 1.25
    pixels into 1.

    For instance, your 1600x1200 image can look fine when viewed on an
    800x600 screen resolution, because two pixels become one - the screen res
    is exactly half the linear measurement of the image res. But when viewed at
    a screen res of 1024x780 (assuming full-size and full-screen), you're
    stuffing 1.56 pixels of image resolution into each screen pixel. Since you
    can't split a pixel, the computer decides which ones to discard entirely,
    and it has to stagger them to keep the image as even as possible. The
    result is often a stepped effect called 'aliasing'. In areas of smooth
    color transition, it isn't very noticeable, if at all. But in areas of high
    contrast you can get weird effects, and in an image with fine patterns, you
    get an 'overlaid' pattern called a moiré, reminiscent of psychedelic swirls
    from the '60s.

    It is exactly related to the patterns that occur when flatbed
    scanning an image printed with a halftone screen, which is made up of dots.
    The dots and pixels clash at regular intervals.

    I looked at your example images, and they look exactly alike to me.
    But I'm viewing them on a monitor at 800x600 res. So try adjusting the
    display size and seeing what happens, especially if you're getting much
    better results when the image is displayed at 50% rather than 66% or
    thereabouts.

    Good luck,


    - Al.
     
    Al Denelsbeck, May 13, 2004
    #3
  4. Mark

    Mark Guest

    Thanks for the post.
    You're right...there is no difference. I posted the wrong links. Here is the correct one. I believe you will see there is clearly a difference in quality. I am looking at the pic in different percentages on the screen -30-50, 80%, etc.

    http://www3.telus.net/public/tmajer_/IMG_0123.JPG


    :
    :
    : > I have been playing with this camera and some pics at 1600x1200 norm
    : > look worse or the same as 640x480 normal while others clearly look
    : > better at the 1600x1200 res. What I mean by worse is that they look
    : > abit more grainy and not as good resolution as if they were taken at
    : > 1mega pixel or lower. I am comparing daylight shots with other
    : > daylight shots and the results are not consistent.
    :
    :
    : Is this occurring when you view the images at 100% on your monitor,
    : or small enough to fit the entire image onscreen?
    :
    : If the latter, I suspect you're running afoul of 'aliasing'. You have
    : a fixed number of pixels in a photo, and a fixed number displayed on your
    : monitor. If the image is displayed in a res not evenly divisible by the
    : monitor res, the display is fudged to account for trying to make 1.25
    : pixels into 1.
    :
    : For instance, your 1600x1200 image can look fine when viewed on an
    : 800x600 screen resolution, because two pixels become one - the screen res
    : is exactly half the linear measurement of the image res. But when viewed at
    : a screen res of 1024x780 (assuming full-size and full-screen), you're
    : stuffing 1.56 pixels of image resolution into each screen pixel. Since you
    : can't split a pixel, the computer decides which ones to discard entirely,
    : and it has to stagger them to keep the image as even as possible. The
    : result is often a stepped effect called 'aliasing'. In areas of smooth
    : color transition, it isn't very noticeable, if at all. But in areas of high
    : contrast you can get weird effects, and in an image with fine patterns, you
    : get an 'overlaid' pattern called a moiré, reminiscent of psychedelic swirls
    : from the '60s.
    :
    : It is exactly related to the patterns that occur when flatbed
    : scanning an image printed with a halftone screen, which is made up of dots.
    : The dots and pixels clash at regular intervals.
    :
    : I looked at your example images, and they look exactly alike to me.
    : But I'm viewing them on a monitor at 800x600 res. So try adjusting the
    : display size and seeing what happens, especially if you're getting much
    : better results when the image is displayed at 50% rather than 66% or
    : thereabouts.
    :
    : Good luck,
    :
    :
    : - Al.
    :
    : --
    : To reply, insert dash in address to separate G and I in the domain
     
    Mark, May 14, 2004
    #4
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