Grain from a Sony A7iii

Started 3 months ago | Questions thread
FingerPainter Veteran Member • Posts: 9,594
Noise is NOT...

gezzamondo wrote:

i took some photos the other day using these settings

f/5.6 70mm 1/160sec ISO 200

I shot slightly under exposed due to shooting directly into the sunset and so i can recover the shadows in lightroom

but when i increased the shadows i noticed a lot of grain even though i only shot at ISO 200

Noise is not:

  1. the same thing as grain
  2. caused by the ISO setting.
  3. caused by lightening an image in development

Details follow below.

Is it normal for it to be so grainy from the sony at those settings?

In that light, yes.

See examples below including histogram

The histogram of the first one indicates you could have exposed a couple stops higher. Had you done so, it wouldn't have been as noisy.

I suggest you read the articles here on DPR about the causes of noise, and how to avoid it.

1. Grain is a physical property of film, due to the coarseness of the light-sensitive particles in the emulsion. B&W films with a higher ISO rating have larger pieces of silver halide so they can react better to diminished light. These larger pieces create a grainier look.

Noise in digital images is not grain. It is not a physical property of anything. It is variation in the digital values of nearby pixels. Most of the variation in pixel values is due to the fact that there is a natural random variation in the arrival rate and colour of photons reaching your camera.

2. When you take a photo of a given scene at {f/5.6, 1/160}, the photo will have nearly the same noisiness if you take it at ISO 1600 as if you take it at ISO 100. That's because both photos will capture about the same amount of light. The noisiness of a digital image depends primarily on how much light was captured by the image.

In fact, on many digital cameras, the image taken at ISO 1600 might be slightly less noisy. On your a7III, the photo taken at ISO 1600 will have about 5/6 stops less noisiness in the shadows. It might blow some highlights though.

Many people associate a higher ISO setting with more noisiness because they use their camera in an auto exposure mode in which they set the ISO manually, but the camera sets the exposure by altering one or both of the shutter or aperture settings. In these modes, if you raise the ISO, the camera responds by reducing the exposure, either by speeding the shutter or narrowing the aperture. Speeding the shutter or narrowing the aperture reduce the amount of light the camera will capture. It is the reduction in light capture that is the cause of the increased noisiness.

Because noise and grain are different things with different causes, they have different solutions too. You avoid a grainy image in film by using a film with smaller particles - one with a lower ISO rating. The way you avoid the noisiness effects of variation in light on digital images is to capture more light. That way, the variations tend to cancel each other out or get hidden.

To make digital image with as little noisiness as possible, use the slowest shutter and widest aperture that don't blow important highlight detail.

Your ISO 200 images are noisy because you didn't capture very much light in them. Using a negative EC or deliberately under-exposing makes an image noisier, because less light is captured.

3. Lightening a digital image in software after capture does not make the image noisier. Operations like bringing up the shadows just apply a fairly simple multiplication to digital values of pixels. Nearby pixels will be increase by about the same factor. That means the variations between them - what we see as noise - won't change.

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