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#1
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Image Size and Compression.
Let's assume I have a 10MP camera
My sensor is say, 3650 X 2740 pixels. But say I want to create an image at 1825 x 1370 pixels. How does the camera actually reduce the 5.0MPs to 2.5MPs Does it choose groups of 4 pixels and somehow average them out to groups of 1 pixel each? How does this process differ from compressing the 10MP image by a factor of 4. I know that in one case the image SIZE is reduced (as well as the file size) whereas in the other case, the image SIZE remains the same but the file size is reduced. How exactly does each process affect the appearance of say an 8x10 print. Bob Williams |
#2
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Image Size and Compression.
bobwilliams wrote:
Let's assume I have a 10MP camera My sensor is say, 3650 X 2740 pixels. But say I want to create an image at 1825 x 1370 pixels. How does the camera actually reduce the 5.0MPs to 2.5MPs Does it choose groups of 4 pixels and somehow average them out to groups of 1 pixel each? How does this process differ from compressing the 10MP image by a factor of 4. I know that in one case the image SIZE is reduced (as well as the file size) whereas in the other case, the image SIZE remains the same but the file size is reduced. How exactly does each process affect the appearance of say an 8x10 print. Bob Williams OOPS! I meant to say, How does the camera actually reduce the 10MPs to 2.5MPs? Bob |
#3
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Image Size and Compression.
On 30/07/2010 10:36, bobwilliams wrote:
bobwilliams wrote: Let's assume I have a 10MP camera My sensor is say, 3650 X 2740 pixels. But say I want to create an image at 1825 x 1370 pixels. How does the camera actually reduce the 5.0MPs to 2.5MPs Does it choose groups of 4 pixels and somehow average them out to groups of 1 pixel each? How does this process differ from compressing the 10MP image by a factor of 4. I know that in one case the image SIZE is reduced (as well as the file size) whereas in the other case, the image SIZE remains the same but the file size is reduced. How exactly does each process affect the appearance of say an 8x10 print. Bob Williams OOPS! I meant to say, How does the camera actually reduce the 10MPs to 2.5MPs? Bob When using a smaller pixel count, what a given camera does exactly is hardly documented. Most processing would be built around these algorithms (in decreasing order or quality and computing power needs): http://en.wikipedia.org/wiki/Lanczos_resampling http://en.wikipedia.org/wiki/Bicubic_interpolation http://en.wikipedia.org/wiki/Bilinear_interpolation http://en.wikipedia.org/wiki/Nearest..._interpolation PC software normally uses the first two. Some pre-blurring, and post-sharpening can be used. This would also be combined with the demosaicing algorithm. -- Bertrand |
#4
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Image Size and Compression.
On Fri, 30 Jul 2010 01:25:37 -0700, bobwilliams wrote:
Let's assume I have a 10MP camera My sensor is say, 3650 X 2740 pixels. But say I want to create an image at 1825 x 1370 pixels. How does the camera actually reduce the 5.0MPs to 2.5MPs Does it choose groups of 4 pixels and somehow average them out to groups of 1 pixel each? How does this process differ from compressing the 10MP image by a factor of 4. I know that in one case the image SIZE is reduced (as well as the file size) whereas in the other case, the image SIZE remains the same but the file size is reduced. How exactly does each process affect the appearance of say an 8x10 print. Bob WilliamsÕÅ?€(¹ Why not try it. You would then know that whatever results you get are real and not guessed at by someone else. -- Neil - reverse 'ra' and delete 'l'. |
#5
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Image Size and Compression.
On Fri, 30 Jul 2010 11:03:33 +0200, Ofnuts
wrote: On 30/07/2010 10:36, bobwilliams wrote: bobwilliams wrote: Let's assume I have a 10MP camera My sensor is say, 3650 X 2740 pixels. But say I want to create an image at 1825 x 1370 pixels. How does the camera actually reduce the 5.0MPs to 2.5MPs Does it choose groups of 4 pixels and somehow average them out to groups of 1 pixel each? How does this process differ from compressing the 10MP image by a factor of 4. I know that in one case the image SIZE is reduced (as well as the file size) whereas in the other case, the image SIZE remains the same but the file size is reduced. How exactly does each process affect the appearance of say an 8x10 print. Bob Williams OOPS! I meant to say, How does the camera actually reduce the 10MPs to 2.5MPs? Bob When using a smaller pixel count, what a given camera does exactly is hardly documented. Most processing would be built around these algorithms (in decreasing order or quality and computing power needs): http://en.wikipedia.org/wiki/Lanczos_resampling http://en.wikipedia.org/wiki/Bicubic_interpolation http://en.wikipedia.org/wiki/Bilinear_interpolation http://en.wikipedia.org/wiki/Nearest..._interpolation PC software normally uses the first two. Some pre-blurring, and post-sharpening can be used. This would also be combined with the demosaicing algorithm. There are dozens more resampling algorithms than that available in good computer software. Like Bell, Spline, Pyramid, Mitchell, Vector, Triangle, Hermite, Catmull-Rom, and all their various incarnations. Bicubic being the most often used in-camera algorithm due to its speed (vs. poorer detail-retaining performance) that is required for fast in-camera processing. I know of NO camera that would ever use the processing intensive Lanczos algorithms. That's just wishful dreaming on your part. Nor do I know of any that would use the rudimentary Bilinear or Nearest Neighbor. Those are just too crude for any in-camera processing. Please only offer advice and opinions on things that you actually know about. It's so tedious having to continually correct you lousy ****-head pretend-photographer role-playing trolls. |
#6
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Image Size and Compression.
On 30/07/2010 11:46, BFD wrote:
Please only offer advice and opinions on things that you actually know about. It's so tedious having to continually correct you lousy ****-head pretend-photographer role-playing trolls. This was just a ploy to trick you into sharing your Immense Knowledge with us mere mortals, O Grand Master Of All Things Photographic... -- Bertrand |
#7
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Image Size and Compression.
On 30/07/2010 09:25, bobwilliams wrote:
Let's assume I have a 10MP camera My sensor is say, 3650 X 2740 pixels. But say I want to create an image at 1825 x 1370 pixels. How does the camera actually reduce the 5.0MPs to 2.5MPs Does it choose groups of 4 pixels and somehow average them out to groups of 1 pixel each? It does (or rather should do) something a little bit more sophisticated than a simple average. It has to low pass filter the image to downsample and avoid producing Moire fringe aliasing artefacts. How does this process differ from compressing the 10MP image by a factor of 4. Critically the top half of the high frequency components present in the orginal image are lost forever when you downsample to a half size one. The information content and size is reduced accordingly. I know that in one case the image SIZE is reduced (as well as the file size) whereas in the other case, the image SIZE remains the same but the file size is reduced. How exactly does each process affect the appearance of say an 8x10 print. Bob Williams The finest visible detail in the 10Mpixel image will be about 1/300" across whereas in the 2.5Mpixel image it will be 1/150". For my money the higher resolution image using higher compression will almost always beat the lower resolution less compressed image. There can be exceptions and unless you are absolutely certain you will never need the extra pixels or you are running out of media space there is little or no advantage in decreasing image size in the camera. Regards, Martin Brown |
#8
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Image Size and Compression.
On Fri, 30 Jul 2010 12:59:32 +0100, Martin Brown
wrote: For my money the higher resolution image using higher compression will almost always beat the lower resolution less compressed image. There can be exceptions and unless you are absolutely certain you will never need the extra pixels or you are running out of media space there is little or no advantage in decreasing image size in the camera. Regards, Martin Brown Showing how little you know. If using higher ISO's with more noise, it can be advantageous to use in-camera downsampling. As this will average-out the noise from the RAW sensor data. |
#9
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Image Size and Compression.
Outing Trolls is FUN! wrote:
On Fri, 30 Jul 2010 12:59:32 +0100, Martin Brown wrote: For my money the higher resolution image using higher compression will almost always beat the lower resolution less compressed image. There can be exceptions and unless you are absolutely certain you will never need the extra pixels or you are running out of media space there is little or no advantage in decreasing image size in the camera. Regards, Martin Brown Showing how little you know. If using higher ISO's with more noise, it can be advantageous to use in-camera downsampling. As this will average-out the noise from the RAW sensor data. It would be more "advantageous" to retain the original data and use a superior noise reduction algorithm later. You can look up noise reduction algorithms on your own time if you think averaging is a good one. BugBear |
#10
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Image Size and Compression.
On Fri, 30 Jul 2010 13:54:47 +0100, bugbear
wrote: Outing Trolls is FUN! wrote: On Fri, 30 Jul 2010 12:59:32 +0100, Martin Brown wrote: For my money the higher resolution image using higher compression will almost always beat the lower resolution less compressed image. There can be exceptions and unless you are absolutely certain you will never need the extra pixels or you are running out of media space there is little or no advantage in decreasing image size in the camera. Regards, Martin Brown Showing how little you know. If using higher ISO's with more noise, it can be advantageous to use in-camera downsampling. As this will average-out the noise from the RAW sensor data. It would be more "advantageous" to retain the original data and use a superior noise reduction algorithm later. Of course it would. But that was not the question nor possible answer. I purposely set all my cameras to lowest contrast (retains fullest dynamic range in the JPG output), lowest noise-reduction, and lowest sharpening settings so that I may do that better on the computer. If available (as in CHDK cameras) I will use a live-view RGB histogram to determine if any one or more of the color channels are also out of whack and will also adjust those accordingly so that one will not be blown-out before another. However, it can be even better to use a RAW-Averaging feature as is available in all CHDK P&S cameras' in-camera processing to provide completely noise-free images at ISO800, 1600, and higher. You speak as if others don't know more than you ever will. |
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