dkeysser Loc: Minneapolis

I recently bought a camera capable of 61 MP, and also capable of two lower settings, 36 and 19. I normally use the 61 MP setting; that is why I bought the camera. But I have noticed that when I am shooting in a very low light situation (hence the need for high ISO), the ISO (set to Auto) my camera comes up with is higher at 61 MP than if I lower my resolution to 36 or 19, with the aperture and SS the same. What exactly is happening? Is there a trade off between the high resolution and the ISO noise? Should I lower my MP setting if I know I am going to be shooting in a very low light situation (a theater, for example)? What are the tradeoffs here?

Thanks in advance for the usual wise information.

Don

ricardo00

Interesting. I assume when you shoot at lower MP settings it uses the same sensor but is combining the info from several individual pixels to make one larger one. Thus this larger individual pixel would collect more light, leading to a lower ISO? I am sure someone more knowledgable will have a better technical description but to me it makes sense, that is why, assuming the same or similar sensor, higher MP cameras have worse low light capabilities.

cahale Loc: San Angelo, TX

Which one looks the best after use. Use that one.

Orphoto Loc: Oregon

That effect has been around for a while. Using my D800 to shoot high school football several years ago, I found that medium and small .jpg s greatly reduced the degree of noise at a high iso.

User ID

Sounds backwards to me. I would disable auto ISO, run a noise comparison comparing 60MP to 30MP, and then Id know which resolution is actually less noisy.

My a9 has shown me that Sony deploys some rather weird and counterintuitive algoriddems concerning high ISO.

Orphoto Loc: Oregon

user id, this finding was on manual iso and the effect was so striking that no testing was needed.

pmorin Loc: Huntington Beach, Palm Springs

I have found that to be the case with my Canon cameras also. I have a 5D4 and a 5Dsr. The 5D4 has a lower pixel count than the 5Dsr and it handles lowlight settings much better with a lower iso.

R.G. Loc: Scotland

Whether a camera is increasing or decreasing resolution, the starting point has to be the sensor's native resolution. Any departure from that is achieved by software, and there's nothing that's done in-camera that can't be done on a computer. In fact the chances are that a computer would do a better job.

When comparing contemporary and similarly sized sensors, high resolution sensors have relatively worse low light, high ISO performance in that they produce noisier images. However, the noise can actually be less noticeable because the pixels are smaller than those of a similar sized lower resolution sensor. At a pixel level the noise from the high resolution sensor will typically be more extreme but it can be less intrusive because the pixels are smaller.

In addition to that, downsampling has the effect of reducing noise, but the downside is a loss of fine detail. However, that loss of fine detail is most apparent when doing side-by-side comparisons, and when viewing a downsampled image in isolation it may appear to be perfectly acceptable.

Side-by-side comparisons are good for showing differences but they tell us little about how the final image will appear when viewed in isolation. The eye can be quite tolerant of things that we sometimes refer to as defects. In fact a loss of fine detail could go completely unnoticed because much of the time, if we don't know what was there in the first place we wont miss it when it's absent.

What is undeniable is that the higher resolution image has more image data as far as detail is concerned. How the sensor data is manipulated, and the final outcome, depends on how the data is processed, and that will be in the hands of either the camera algorithms or the person doing any computer post processing. Much depends on the sophistication of the software, and as far as I know, there's nothing special about in-camera processing. In fact the chances are that computer software will be the more sophisticated of the two, and if properly used it will produce the better result. The in-camera processing has the advantage that it's automatic and therefore more convenient and time-saving.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

With todays AI in Photoshop and Lightroom there is really much less concern with that than in the past.
I shoot the Sony a1 at 50 MP all the time. Noise is not an issue at high ISO with Photoshop AI.
Do not worry about that, use whatever you need to get the shot, let Photoshop and Lightroom take care of noise and resolution after you get your shot.
In the image below I used a very high iso to get the shot at 50 MP, after cropping in Photoshop and topaz AI, the shot came out fine.

13 Loc: I am only responsible to what I say..not what

Beautiful shot and in part, agree with your statement. Nice!!!!

User ID

I guess youre referring to your experience with your Nikon 850 ??

The OP clearly stated that his observation involved *auto* ISO on a Sony (a7R-IV).

I have Sonys and Nikons. The Z7 Nikons are normal. I dont have the exact same Sony as the OP, but my a9 (my highest tech in Sony) is NOT normal concerning high ISO. High ISO is blocked in more conditions than its allowed. Maybe due to the stacked sensor design ????

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

The Sony a7 r IV has a reputation for poor performance at high ISO's. That is why I sold mine after a month of shooting and went with the Sony a1.

one_eyed_pete Loc: Colonie NY

Your finding does seem illogical. The difference between JPEG small, medium and large is the degree of file compression after processing of the raw data to create the JPEG image file. Perhaps your observation was the noise reduction resulting from the JPEG algorithm doing it's thing to further compress the resulting image file.

dkeysser Loc: Minneapolis

Good question. I haven't had a chance to print them yet. On the screen, I see only a small distinction, so I need to print them large to find out. Thanks.

bwana Loc: Bergen, Alberta, Canada

I use a Sony A7R V (~60MP) in low light with good results; however, you are correct in a sense, the noise appears less when shooting in Medium or Low resolution. The reason; the camera is averaging pixels thus reducing the apparent noise.

I seldom shoot at Medium or Low resolution (I use my A7 III for that). I use Topaz DeNoise AI or Photo AI to handle the noise, i.e.: I really hate losing the high resolution for which I bought the camera!

Comments from a Photo magazine article:
"When you reduce a noisy picture from its original sensor size to a smaller size you will always find that some of the noise disappears. This is not a defect in the camera, you will see the same thing if you shoot 12MP and then reduce the picture in Photoshop.

The reduction algorithm takes a bunch of noisy hi-res pixels and averages them down into less pixels in the reduced image. You can define noise as pixels that have a higher or lower value than the correct value. When you average a few pixels together some of the noise will cancel out, since you will be mixing pixels that are too high with pixels that are too low. The end result is that the smaller image has less noise.

If you want less noisy 12MP pixels, then switch to P mode (or any other manual or semi-manual modes) and use as low ISO as you can.

Another option to get less noisy images is to mount the camera on a tripod and shoot 2 or 3 or as many pictures as you want at 12MP, all identical. Take all those pictures into Photoshop or GIMP and average them out. This averaging has the same effect on noise that a size reduction has without actually reducing the picture."

The last item above is the approach used by astro-imagers. In this case the signal-to-noise ratio improves by the square root of the number of subs combined, i.e.: nine subs would improve the SNR by 3x. Some cameras even allow you to do this in-camera.

bwa