topic Re: ISO and downsampling in General Discussion

ISO and downsampling

Tedphoto — Mon, 21 Jun 2021 21:45:10 GMT

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?

Re: ISO and downsampling

rs-eos — Mon, 21 Jun 2021 22:37:39 GMT

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.

Re: ISO and downsampling

kvbarkley — Mon, 21 Jun 2021 22:38:48 GMT

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"

Re: ISO and downsampling

jrhoffman75 — Mon, 21 Jun 2021 23:04:16 GMT

@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?

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)

Re: ISO and downsampling

Mark35mmF2 — Tue, 22 Jun 2021 07:55:57 GMT

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.

Re: ISO and downsampling

ebiggs1 — Tue, 22 Jun 2021 13:50:09 GMT

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

New technology will almost always trump any older tech.

Re: ISO and downsampling

kvbarkley — Tue, 22 Jun 2021 13:59:33 GMT

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

Re: ISO and downsampling

ebiggs1 — Tue, 22 Jun 2021 14:03:46 GMT

"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.

Re: ISO and downsampling

ebiggs1 — Tue, 22 Jun 2021 14:08:37 GMT

"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!

Re: ISO and downsampling

ebiggs1 — Tue, 22 Jun 2021 14:12:57 GMT

"... 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.

Re: ISO and downsampling

johnrmoyer — Tue, 22 Jun 2021 16:30:33 GMT

Since the noise from high ISO seems to mostly be extreme values when compared to surrounding pixels, a median filter will make the noise more like the surrounding pixels which makes the noise less visible, but also blurs the image. Down sample and sharpen after a median filter will result in a lower resolution image that sometimes will look better than the higher resolution original. If a higer resolution image is needed, then this will not be useful, but if a lower resolution image can be used then it is worth trying. Gimp or graphicsmagick will do a median filter and resample.

Here is a down sampled noisy 25600
ISO image: https://www.rsok.com/~jrm/2021May26_birds_and_cats/2021may22_fox_IMG_1312c.html

I used graphicsmagick on a Debian Linux computer to do the downsample after converting the raw CR3 file to JPEG using DPP on an iMac. DPP did a lot of noise reduction leaving a very soft image but did well at preserving colors. The downsampling took an unusuable fuzzy and noisy image and changed it into an interesting but not perfect images of a fox eating bird seed, grape jelly, and a strawberry. Illumination was a porch light and the photo was made from inside my house though a double pane window which further distorted and softened the image. Down sampling also made some of the motion blur from the slow shutter speed and the fox moving less obvious.

The graphicsmagick command line used was (extra quotes around ':' to keep it from turning into emoticon):

gm convert -verbose IMG_1313c.JPG -resize "37.5%" -unsharp 0x1 -mattecolor black -frame 16x16 -font helvetica -fill white -draw "text 4,1228 'Gray Fox (Urocyon cinereoargenteus), May 22, 2021, Copyright http://www.rsok.com/~jrm/ All rights reserved.'" -define 'jpeg:dct-method=float,jpeg':'optimize-coding=true' -interlace line -quality 97 2021may22_fox_IMG_1313c.jpg

F Number	5.0
ISO	25600
Shutter Speed Value	1/83
Focal Length	286.0 mm
Focus Distance Upper	10.47 m
Focus Distance Lower	8.99 m
Lens Model	EF100-400mm f/4.5-5.6L IS II USM

Re: ISO and downsampling

ebiggs1 — Tue, 22 Jun 2021 21:12:37 GMT

Kinda looks like an over use of the clarity slider.

Re: ISO and downsampling

Waddizzle — Tue, 22 Jun 2021 21:24:05 GMT

The graphicsmagick command line used was (extra quotes around ':' to keep it from turning into emoticon):

F Number	5.0
ISO	25600
Shutter Speed Value	1/83
Focal Length	286.0 mm
Focus Distance Upper	10.47 m
Focus Distance Lower	8.99 m
Lens Model	EF100-400mm f/4.5-5.6L IS II USM

-----------------------------------------------------------

I never new that 1/83 shutter speeds were possible with a Canon camera body. Those settings are recipe for a poor image.

Re: ISO and downsampling

ebiggs1 — Tue, 22 Jun 2021 21:31:55 GMT

I tought them odd too. But it did produce a nice photo. However, I believe I could do something similar with the clarity slider in LR.

Re: ISO and downsampling

johnrmoyer — Tue, 22 Jun 2021 21:55:23 GMT

Clarity slider was at 2.
Unsharp mask was 2.0,4.0,4.0 with additional unsharp mask applied after down sampling.

Digital Lens optimization was at 40.8.

Noise reduction was at 12.0 for both Luminance and Chrominance.

Setting Clarity slider to 0 instead of 2 makes very little difference. The image was very soft because of 25600 ISO, noise reduction, motion by the fox, slow shutter speed, and dual pane window glass with reflections. The point was to show that downsampling can be useful for rescuing a photo made under difficult conditions.

The Fox moved less and posed better in this one:

@ebiggs1 wrote:
Kinda looks like an over use of the clarity slider.

Re: ISO and downsampling

johnrmoyer — Tue, 22 Jun 2021 22:11:35 GMT

It was aperture priority and auto shutter speed and I had guessed that 25600 was the highest ISO I could get by with. So far as I know, with aperture priority the shutter speed might be set automatically to any arbitrary number. The fox came while we were watching television and only stayed a couple minutes. The porch light was on, but else it was completely dark at the tree stump where I feed birds. I went into the other room to get my camera and was able to return without scaring the fox. The photo was made through double pane window glass which provided distortion and reflections. The point of posting was to demonstrate that down sampling can rescue a photo made under difficult conditions. The original question was about downsampling and high ISO noise and not about making a photo under optimal conditions so far as I can remember.

Maybe if I had paid my foxy model better I could have gotten a studio shot with proper lighting 🙂 The only pay was bird seed and fruit on a tree stump.

"
Measured EV                     : 3.12
Measured EV 2                   : -16.5
" from Exif data.

@Waddizzle wrote:

-----------------------------------------------------------

I never new that 1/83 shutter speeds were possible with a Canon camera body. Those settings are recipe for a poor image.

Re: ISO and downsampling

ebiggs1 — Wed, 23 Jun 2021 16:30:11 GMT

"Clarity slider was at 2."

I understand. I figured it was set fairly low. I merely remarked that I think you could get the same appearing photo with the clarity slide set pretty high. In photography there is no free lunch. You always give to get.

Many, many ways to achieve the end result.

Re: ISO and downsampling

ebiggs1 — Wed, 23 Jun 2021 16:32:08 GMT

"... bird seed and fruit on a tree stump."

Perhaps I should have said there is no free lunch, ... most of the time!

Re: ISO and downsampling

ebiggs1 — Wed, 23 Jun 2021 16:38:57 GMT

"I used graphicsmagick on a Debian Linux computer to do the downsample after converting the raw CR3 file to JPEG using DPP ..."

You may as well be talking Chinese. I use and have never really used anything else besides Photoshop and Lightroom. I do have DPP4 installed on my Windows 10 computer but rarely use it.

Re: ISO and downsampling

rs-eos — Wed, 23 Jun 2021 17:09:08 GMT

"I used graphicsmagick on a Debian Linux computer to do the downsample after converting the raw CR3 file to JPEG using DPP on an iMac."

Didn't catch this earlier... It would be better to downsample from say a 16-bit Photoshop or some other 16-bit per component file (something with uncompressed or lossless compressed data). By first going to JPEG, you'd end up with just 8-bits per component as well as dealing with lossy compression. The final output (also assuming JPEG) would then be second-generation, so more info lost.