Does ISO effect Image sharpness?

AfternoonTea · May 20, 2013

I know sharpness has many factors such as lenses, sensor, resolution. I also know that A smaller ISO setting has less noise than a higher setting so a smaller ISO in theory gives apparent sharper images than a higher ISO value. Lets say if we were to narrow it down to a controlled environmental setting. Lighting is perfect, and lets fix the F-stop to the same setting, and its sweet spot.

Our camera is on the tri-pod; We are in focus, depth of field, white balance, everything is set . The only thing we need to change is the ISO, and Shutter speed which can compensate to our perfect lighting and no compromise with F-stop is needed.

My question is does ISO really effect overall image sharpness?

Before posting this I read many things, and previewed tons of photos on flicker and compared there specs. Does ISO matter in terms of sharpness with the controlled. Obviously ISO 1600+ will look very noisy. So lets stay around ISO 100 or less - 800.

I typically like ISO 100 (in good lighting, and compensate the shutter) since its the least noisy on my camera, but will bumping it up (causing more noise) effect its sharpness? I read that ISO noise does not effect sharpness that a sharp picture is a sharp picture, and its (not literally since its cause by technical things) almost like noise (grain) added over a picture.

waterbeef · May 20, 2013

Noise caused by high ISO ruins a photo.
Sharpness is meaningless to a ruined photo.

Benco · May 20, 2013

Depends whether you want a given level of noise in the photo, applying a lot of noise reduction to high ISO photos will soften them.

spmakwana · May 20, 2013

ISO have nothing to do with sharpness of photo, more ISO the more noise.

runnah · May 20, 2013

waterbeef said:
Noise caused by high ISO ruins a photo.

Well that is just subjective.

Anyways. It's all about finding the balance in the given situation. Just leaving the ISO on 100 and expecting sharp images will give you bad results, and vice versa with high ISO. So read up up on which lighting situations call for which ISO.

CaptainNapalm · May 20, 2013

High ISO does not take away from image sharpness. Post processing to reduce the noise caused by high ISO setting does.

DSRay · May 20, 2013

It seems to me, the best way to answer your question is to try it; you'll never know until you do.

curtyoungblood · May 20, 2013

I tend to push my ISO abilities to the edge, and I do tend to feel like it is difficult to get really crisp photos at a higher ISO. However, this could be related to the quality of the light, AF having trouble in low light, etc.

TCampbell · May 20, 2013

If you're shooting in JPEG, then the answer is yes. If you're shooting in RAW then the answer is "maybe" -- it depends on what you do in post processing.

When you shoot in JPEG, the camera will automatically reduce noise. You can often see this happen at specific thresholds. For example... I've seen ISO/noise graphs which show the camera going from 100, 200, 400 with each step having progressively more noise (albeit a small amount) and then at 800 suddenly the camera has less noise than it had at 400. That's because at 800 the camera kicks in a specific aggressiveness of noise reduction. It'll go up a few more stops and then kick in an even more aggressive reduction.

Noise reduction has the side-effect of softening an image.

However... if you're shooting in RAW then there's no built-in noise reduction. Any noise reduction that occurs would have to be done in post processing by you. You can decide whether or not you perform noise reduction and how aggressive you want to be. Technically any level of reduction will soften the image somewhat... but no reduction leaves aberrant pixels which you generally don't want to see. I don't fully cook out the noise... I tend to just try to process it down somewhat (and to do that, I use a plugin named Imagenomic NoiseWare Pro -- which offers more control over how the noise gets reduced.)

KmH · May 20, 2013

AfternoonTea said:
Does ISO effect Image sharpness?

No. At least not directly.
Many DSLR cameras today perform quite well at ISO 1600+
But you probably don't yet understand what sharpness is, a combination of acutance and resolution.

Acutance is about how quickly image information transitions at an edge. Lens quality and post processing affect acutance. Image sharpening alters/enhances acutance.
Resolution is about the camera image sensor's ability to show closely spaced details.

Image noise comes in several forms and can be an issue even at ISO 100 if an image is under exposed, or has dark (underexposed) areas.

At higher ISO settings making sure the exposure is accurate helps minimize image noise.
For digital images, at any ISO setting, the best results are generally attained when we Expose-To-The-Right (ETTR) on the histogram.

Tutorials ? Sharpness
Digital Camera Image Noise: Concept and Types

ETTR
Optimizing Exposure

Tailgunner · May 20, 2013

CaptainNapalm said:
High ISO does not take away from image sharpness. Post processing to reduce the noise caused by high ISO setting does.

I'm really new but this makes sense to me. I mean you loose a certain degree of sharpness using glass to begin with and offset this with the sharpness settings in your post process software. So it only makes that you could offset some ISO differences with the same sharpness feature.

amolitor · May 20, 2013

Random remarks, in no particular order:

Resolution depends on the lens and the sensor. ISO doesn't matter, and neither does exposure. If I underexpose by 20 stops, I have just as sharp an image as when I expose correctly -- it just happens to be rendered entirely using black pixels.

Acutance is a different story, and the overall psycho-visual perception of "sharpness" is quite another story as well. The sharp but entirely black image exhibits no actuance at all, and does not appear sharp at all, of course.

Noise can actually increase the perception of sharpness, up to a point, and under certain circumstances. Noise can also increase the information content of an image, in certain cases, and in certain pretty specific ways. Information content isn't the same thing as sharpness, but it related.

HughGuessWho · May 20, 2013

Using high ISO in and of itself does not effect sharpness. However, high ISO will introduce noise. The removal of that noise with noise reduction software will soften an image. Therefore, High ISO and image softness are indirectly related, I guess you could say.