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Old Jan 23, 2009, 8:16 AM   #1
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I have a 3MP camera over 5 years old that takes great quality 640 x 480 pic when I use the VGA setting on the camera, but my 5MP Panasonic takes absolutely horrific picture using the VGA mode.

If I take it at 5MP, then resize it on my computer, it looks decent.

What's the deal with this?
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Old Jan 23, 2009, 8:27 AM   #2
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It depends to a great extent on how the image is downsampled, and what the resolution of the original image has. If you start with an image with a resolution of, say, 1920x1440 and want to convert it to a 640x480 image, that's easy. Each group of 3x3 pixels in the original is averaged to produce a single pixel in the result. But for anything other than that, the camera will have to use dropped pixels over and over again to calculate what the resulting pixels will look like.

ANd the Bayer filter can throw another monkey wrench into all those calculations, depending on wherethe downsampling occurs. And remember that the CPUs in cameras aren't the most powerful. If they were, the battery would need to be a lot bigger.
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Old Jan 23, 2009, 6:56 PM   #3
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TCav wrote:
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It depends to a great extent on how the image is downsampled, and what the resolution of the original image has. If you start with an image with a resolution of, say, 1920x1440 and want to convert it to a 640x480 image, that's easy. Each group of 3x3 pixels in the original is averaged to produce a single pixel in the result. But for anything other than that, the camera will have to use dropped pixels over and over again to calculate what the resulting pixels will look like.

ANd the Bayer filter can throw another monkey wrench into all those calculations, depending on wherethe downsampling occurs. And remember that the CPUs in cameras aren't the most powerful. If they were, the battery would need to be a lot bigger.
Taken at max resolution, then resampled to VGA using Lanczos method and saved at 87 setting in Irfanview


Same camera was set to take photo at VGA Image is clearly inferior.



Different camera taken at max resolution, then resized using same software


The camera used at 640 x 480 setting not so much diff
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Old Feb 18, 2009, 8:17 PM   #4
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To start with, you have to understand that changing the camera's resolution setting does not change the resolution at which the camera "takes" the picture. It always takes the picture at its full resolution. The resolution setting merely chooses between saving the full resolution image or whether its downsampled with the camera's software before saving. When you change cameras you change the downsampling software thats in the cameras firmware. Some is better than others.

Various factors come into play, not the least of which are the size factors mentioned in the first reply. Scaling between some sizes is easily as the sizes are integral multiples of each other. Also, some camera software/firmware is optimized for quality, some for speed, or anywhere in between.

Software running in the camera is always a compromise due to the limited memory, low power processors (read: must be cheap and use little power so the battery can be small), and customer's demand for fast saves (read: high frame rates when shooting in continous). Don't expect it to be the best for all uses. If you want the best quality downsampling, expect to use external software running on a decent computer.
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