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03-12-2018, 08:55 AM - 1 Like   #1
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Combine pixels for higher sensitive possible ?

Hi there,

AFAIK sensor with larger pixel size gather light better, so I wonder if it is possible to combine pixels thus reduced resolution will have the same effect ? I am talking about s/w process, say, combine 4 pixels into one in a 24M sensor like the K3 to make it a 6M one to improve low light sensitive, can that be done if I can sacrifice high shutter speed and anti vibration ? if I remember right this is no news some cameras actually have this option built in but I can't recall which one and why no longer used in new models it is just a s/w thing ?

03-12-2018, 09:10 AM - 1 Like   #2
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You can always use the very practical multi-exposure function on modern Pentax DSLRs with auto EV adjustment and take several exposures of the same scene (4-8-12- ...) and have the camera combine and save these exposures as one file. This is known to even out noise and create a sharp and detailed picture of static subjects. Movement - such as a waterfall - will be blurred and resemble the effect of long exposure with a neutral density filter.
This function makes it possible to take high iso pictures with relatively low noise.
The image size in pixels will remain the same.
03-12-2018, 09:17 AM - 1 Like   #3
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Yes, you can sum four pixels together to get one big, more sensitive, less noisy pixel. On noise issues, summing is not quite as good as a true big-pixel camera due to having four read-noise levels in the sum versus only one in the big pixel camera. On resolution and aliasing, summing small pixels is better than using big pixels due to Bayer color filter issues.

Overall, you'll get about 1 EV improvement in DR and high-ISO performance from a 4-pixel sum. (For statistical reasons, the 4-pixel sum has 4 times the signal but 2 times the noise which gives a net 2X improvement in signal-to-noise ratio)

Summing has no effect on shutter speed and actually helps SR somewhat in that any uncorrected vibration will be half as bad when pixel-peeping the summed image.
03-12-2018, 09:20 AM - 1 Like   #4
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QuoteOriginally posted by lotech Quote
Hi there,

AFAIK sensor with larger pixel size gather light better, so I wonder if it is possible to combine pixels thus reduced resolution will have the same effect ? I am talking about s/w process, say, combine 4 pixels into one in a 24M sensor like the K3 to make it a 6M one to improve low light sensitive, can that be done if I can sacrifice high shutter speed and anti vibration ? if I remember right this is no news some cameras actually have this option built in but I can't recall which one and why no longer used in new models it is just a s/w thing ?
Downsampling is a common noise reduction technique. You can certainly use it (in post) to get clean-looking lower res files.

Or better yet, as others have mentioned, combining multiple exposures can further help reduce noise while maintaining high resolution.


Adam
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03-12-2018, 09:34 AM - 1 Like   #5
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Yes guys, but it would be more convenient to have all that done on camera in one shot than in post, that's why I said about the lower shutter speed, and I've never used the multi exposure I completely missed that !
03-12-2018, 09:41 AM - 1 Like   #6
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QuoteOriginally posted by lotech Quote
I wonder if it is possible to combine pixels thus reduced resolution will have the same effect ?
QuoteOriginally posted by Adam Quote
Downsampling is a common noise reduction technique.
QuoteOriginally posted by lotech Quote
Yes guys, but it would be more convenient to have all that done on camera in one shot than in post, that's why I said about the lower shutter speed, and I've never used the multi exposure I completely missed that !
Shoot lower resolution in-camea JPEG. That is done by downsampling and will provide the functionality you suggested.


Steve
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