Graininess and ISO

[ElNico]

I know that turning the ISO up too much can cause photos to come out grainy; my question is, is this a result of the ISO being too high period (as is implied by the fact that adjusting the ISO instead of the f-stop or shutter speed to compensate for low lighting can result in a grainy image, even though the resulting light level may be good), or does the graininess come from a combination of the ISO and how much light is entering the camera? I ask this because I have some recent grainy images in bright sunlight, where I don't think the brightness of the image is too highin and of itself, and I'm pretty sure the ISO wasn't particularly high.

Suppose I'm shooting while the sun is behind the clouds, and the camera's settings are all good; good brightness, not blurry, not grainy. Then the sun comes out. I adjust the f-stop and/or the shutter speed such that the image is not TOO bright, but still on the bright side of what is good. Do I need to worry about turning down the ISO purely for the sake of reducing graininess, even though the image wasn't grainy before with the current ISO when the lighting was lower?

Thanks all.

 

[Overread]

Note in general grain is a term used with film photography whilst digital refers to noise. Whilst the two appear roughly similar they are very different mechanically and the grain effect is often considered a more visually pleasing effect than noise, which is almost universally disliked
The grainy/noisy effect in a photo is generated by two key aspects

1) Higher ISOs. Raising the ISO will increase the amount of noise in the photo.

2) Underexposure which is then brightened in editing.

It is further important to note that if you underexpose and brighten the level of noise you get is greater than if you'd kept all other settings the same and increased the ISO to achieve a proper good exposure.

Note for that purposes of noise a "correct exposure" is having as much light data as possible without over exposing the photo. This means that if you were to view the histogram you'd have the bulk of the graph on the right side without actually hitting the furthest right side. This method is called "expose to the right" and is a standard theory people use with regard to digital photography; although it should be noted that other factors (light level, creative choices et c..) might well result in you not always exposing to the right perfectly for every shot (indeed most times you won't, but you'll be working with it in mind).




Note that newer sony based sensors are re-writing this theory somewhat as they generate very little noise when brightening a photo in editing. As such this theory holds true for some brand and cameras more than others.

 

[Braineack]

before this thread ends in a bunch of technical mumbo-jumbo that doesn't really matter to you (including but not limited to grain vs. noise, and how ISO works), let me just answer your question:

Do I need to worry about turning down the ISO purely for the sake of reducing graininess, even though the image wasn't grainy before with the current ISO when the lighting was lower?

yes. ISO introduces noise. Good practice is try aim for the lowest ISO possible with your shutter/aperture setting to achieve the exposure. A bright day shot at 6400ISO will still be noisy, but it is exaggerated where light is limited. Better sensors can handle each condition better than others.

 

[ElNico]

Let me show you what I'm talking about. I could be imagining it.

The second and third images are the ones that I feel have this problem. I think the difference is most notably in comparison to the first image, but I think that the fourth one also looks better in this regard, and I included the fourth image mainly to show a "good" one that has a similar amount of zoom to the second and third.

These images are unedited, except to shrink them down so that I could upload them here. Each has been shrunk by the same amount, 50% by 50%. I don't think that the second and third images have a higher ISO, and if so not by much (and I don't see why I would have increased it, since I only would have increased it if the lighting level went down, not up).

I might not consider the second and third images to be noisy at face value, until I compare them to the first image and to a lesser extent the fourth image, which just look... smoother, as though the resolution were finer. This is a lesser version of what I THINK having too high an ISO is supposed to do to an image, and I suspected that was the problem since the second and third images have much stronger light, yet not TOO bright (at least I don't think so).

Is this my imagination? Is the problem (such as it is) actually something else?

 

[Braineack]

it's not "grainy" it's just not a good sensor. I think you have some post-processing being automatically applied to the image, as well as it being compressed poorly and downsized. if these are straight out of the camera, I'm assuming it's running noise reduction on them and your saving low-quality jpgs at 4mp, when you have a 16mp sensor.

the 1/80sec shutter speed didn't help.

 

[ElNico]

it's not "grainy" it's just not a good sensor. I think you have some post-processing being automatically applied to the image, as well as it being compressed poorly and downsized.

So, I was correct in thinking that the issue was with how the camera is processing its input (whereas f-stop and shutter speed are mechanical parameters), but the processing in question isn't the ISO, it's something else?

The camera is a point and shoot, so I find this easy to believe.

if these are straight out of the camera, I'm assuming it's running noise reduction on them and your saving low-quality jpgs at 4mp, when you have a 16mp sensor.

If it's running noise reduction, that would imply that the image would otherwise have noise, yes? So do I deal with that the same way one would normally try to reduce noise in an image? How do I do that other than by lowering the ISO?

the 1/80sec shutter speed didn't help.

...Dude, I did not realize that JPGs carried that information. N00b alert. (As you can probably guess, I haven't been doing this for very long. )

These images were shot in Aperture Mode, so the shutter speed is the automated parameter. In both the second and the third images, the f-stop was 8 and the ISO was 100 (and yes, as I thought, the ISO is the same in all four of these pictures). Which of those do you think it would have been better to change to make it adjust the shutter speed? Should I have raised the ISO, or reduced the f-stop?

...Actually, looking at those numbers, something weird seems to be going on. I believe that's a low ISO and a VERY high f-stop (correct me if I'm wrong), which is presumably the result of me trying to make the image darker. If the resulting automated shutter speed was "too slow" and image is STILL on the bright side, what gives? It seems to me that the automated shutter speed ought to have been faster in this situation. The automated system seems to be aiming for too high an exposure level; why would it do that, and what can I do about it?

 

[snowbear]

I suspect the embedded software tries to stay near 1/60 or something like that, so it will adjust the other settings.

 

[TCampbell]

It looks like a small image file ... the EXIF data says it was 4608 x 3456 but the image posted is 2304 x 1728 (1/4 size) so there may be some JPEG resampling and compression issues. I don't see issues that I would characterize as "noise".

 

[ElNico]

I suspect the embedded software tries to stay near 1/60 or something like that, so it will adjust the other settings.

No. I set the f-stop and ISO, and the software then picks a shutter speed based on those settings and the lighting. Or at least, I'm told that's how Aperture Priority Mode works, which is what I set it on (the "A" in the settings labeled MASP). My confusion is that the image could stand to be darker AND (according to Braineack) the shutter speed it picked is objectively low, so I don't understand why it didn't pick a faster speed.

It looks like a small image file ... the EXIF data says it was 4608 x 3456 but the image posted is 2304 x 1728 (1/4 size) so there may be some JPEG resampling and compression issues.

It was originally 4608 x 3456, but I resized it by 50%x50% to reduce the file size, so that I could upload it in my post.

I don't see issues that I would characterize as "noise".

You don't think that the image quality of the second and third pictures looks inferior compared to the first one? Again I'm not sure if I'm imagining this or not. Maybe I'm judging too harshly?

 

[ElNico]

I think you have some post-processing being automatically applied to the image, as well as it being compressed poorly and downsized. if these are straight out of the camera, I'm assuming it's running noise reduction on them and your saving low-quality jpgs at 4mp, when you have a 16mp sensor.

I just realized that this is making the same mistake as TCampbell, thinking the camera is reducing the resolution. The reason why the images are 1/4 the size they're "supposed to be" is because I resized them so that the files would be small enough to upload. I did this to all four photos, I resized them all by the same amount (exactly 1/4), and that's the only edit I made.

So, no-one has still answered my main question here... do you agree that the second and third images look less smooth compared to the first and fourth or is it just me, and if so what is the cause of that and what can I do about it?

It's not just the shutter speed, because the first picture has the same speed and the fourth one is even slower. Unless I just did a better job of keeping the camera still in those cases. I don't think that the second and third images look blurry, but I could be wrong.

 

[Braineack]

I think they all look the same in the regards to image quality. I see a lot of jpeg artifacts/compression in all four.

In the first shot, look how little detail there is on the sequins or hair. But I think it appears to have more fine detail, simply because the subject is much larger in frame and the background is out of focus.

the rest of the shots, the aperture is at f/8, so everything is in focus, and the subject is further away, so less pixels to make out details.


what quality setting is your camera set at? what noise reduction setting is it set at?

 

[ElNico]

In the first shot, look how little detail there is on the sequins or hair. But I think it appears to have more fine detail, simply because the subject is much larger in frame and the background is out of focus.

the rest of the shots, the aperture is at f/8, so everything is in focus, and the subject is further away, so less pixels to make out details.

This is why I included the fourth image; it's not a closeup, but is another one that I thought looked smoother compared to the second and third.

It's looking like it was just my imagination. Maybe an illusion due to the harshness of the lighting.

what quality setting is your camera set at? what noise reduction setting is it set at?

Quality is 16mp. As noted above, that was reduced by 1/4 when I resized the images. Noise reduction is set at Standard, the middle of three settings.

I see a lot of jpeg artifacts/compression in all four.

Possibly due to my resizing them and then resaving in jpeg.
In general, how do I avoid jpeg artifacts/compression? I have no idea, except for just not saving in jpeg. I normally save images in PNG for this exact reason, but in this case I didn't because the goal was to reduce the file size, and saving in PNG makes the file size much larger than jpeg.

 

[Braineack]

"noise reduction" should be relabeled as "detail destruction".
keep it off.

png is great, but if your camera is first saving them compressed and lossy...

 

[ElNico]

Good to know, thanks.