ISO and downsampling

[Tedphoto]

I have a question: It used to be that lower mp cameras had better high iso performance because of larger photosites on the sensor. Now I am reading that is no longer true because a down sampled image from a larger mp camera can take advantage of the increased photosites to create an image with less noise when downsampled. I’m wondering if this only applies to an image that is processed as a jpg in the camera? Is there a way this would also work when editing a raw image in LR or Canon’s software?

[rs-eos]

That would have to be a very high resolution sensor since oversampling doesn't just cut resolution in half, it at least cuts in by a factor of four.

Thus, for a 45 MP sensor, you'd end up with on around 11 MP pixel images.  No thanks; I'd take an 18 to 20 MP sensor with larger sensor sites over that.

[kvbarkley]

That is up to LR, I don't think DPP does it.

I don't think it is done in camera either except for specialized modes like "candle light mode"

[jrhoffman75]

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@Tedphoto wrote:
I have a question: It used to be that lower mp cameras had better high iso performance because of larger photosites on the sensor. Now I am reading that is no longer true because a down sampled image from a larger mp camera can take advantage of the increased photosites to create an image with less noise when downsampled. I’m wondering if this only applies to an image that is processed as a jpg in the camera? Is there a way this would also work when editing a raw image in LR or Canon’s software?

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Welcome to the forum.

It is my understanding that true downsizing is a mathematical process different than the compression that takes place when a RAW file is converted to a JPEG file in camera.

Some cameras have a crop mode where only a portion of the image file is marked off, but that simply cuts out a portion of the image file when it is exported, resulting in a smaller file size.. 

For example, an EOS R5 is a 45MP full frame camera, but if the APS-C crop mode is selected the resulting file is 17.3MP (45 divided by (1.6 squared [or 2.56])

Canon : Product Manual : EOS R5 : Specifications (start.canon)

[Mark35mmF2]

Hi there,

All other factors being equal, a larger photo site will make a "cleaner" image, although increases in sensor technology do allow for smaller photosites to perform better than previous generations, and then the downsampling you mention can help to manage noise even more, but as was mentioned above that process is primarily done in the post-processing stage. So the noise I would have seen on my old EOS 20D, being 8 megapixels on an APS-C sensor and thus having larger photosites, is not going to be as "clean" as a similarly exposed file from an EOS M50 at 24 megapixels on the same size sensor just because of the advances in sensor and processor technology in that time. Keeping in mind that heat and power consumption also contribute to noise generation (this is what causes noise in higher ISO images, the base electrical signal is being amplified) a newer sensor with redesigned photo sites will also tend to use less power. So there are a number of factors that will affect noise in general and phtoto site size will only be one of them, but it is still true that larger photo sites will collect light easier and thus contribute to less noise. This is why Cinema EOS cameras and specialty cameras have specific pixel counts to correspond to their specific use or range of uses, to allow for the largest photosites possible. It is just not the primary driving factor in noise reduction now, rather one of a mix.

[ebiggs1]

"Now I am reading that is no longer true because ..."

New technology will almost always trump any older tech.

[kvbarkley]

Not always, cf the F-15 and F-16 vs the F-35.

[ebiggs1]

"Not always, cf the F-15 and F-16 vs the F-35."

I've never used any of those cameras, so I can't say! 

[ebiggs1]

"I’m wondering if this only applies to an image that is processed as a jpg in the camera? Is there a way this would also work when editing a raw image in LR or Canon’s software?"

I am not exactly sure how Canon's DPP4 edits but I assume it is similar to Adobe (PS/LR).  So, neither uses a jpg or the Raw file but their own conversion to accomplish the edits. Down or up sampling in this case. A jpg is the method of saving the photo file. If you have a Raw file it is never edited but a tag is created with the edits saved there.

[ebiggs1]

"...  no longer true because a down sampled image from a larger mp camera can take advantage of the increased photosites ..."

I would also add, it depends on two things. The actual photo and the method used to down sample it.  Some photos may benefit and some may not. I think those two things will weight more on it than the size of the sensor or photosites on it.