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So, I took this shot indoors (bright sunny outside) using on a Nikon D5200 with A priority and Auto ISO:

Light by a door on the right and a silver reflector on the left

Photo looks ok when zoomed out. But when I zoom 1:1 in LightRoom, I see some blue specks in the photograph (bottom right) and also a very grainy picture.

Blue specks on bottom right & grainy picture at 1:1

Camera settings were as below:

Camera Settings

I read somewhere that the graininess/noise could be an artifact of high ISO (1600). Is that true? Also, what could be causing the blue specs? What range of ISO would be optimal for this kind of indoor shoot?

Is there a filter available in Lr for removing this noise?

UPDATE: Those blue specs disappear with the Luminance (Develop->Detail->Noise Reduction) set to a value of 40.

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The blue specks are read noise that is being amplified when you try to pull details out of shadows that are pretty much pure black.

Noise is a result of low signal-to-noise ratio (SNR). In the case of digital photography signal is determined by the amount of light allowed to hit the sensor. Noise is a combination of constant read noise caused by the electronics of the sensor and other electrical components between the sensor and the analog-to-digital convertor and photon shot noise caused by the random nature of light.

The reason that noise is often attributed to using a high ISO is because higher ISO settings are used to allow proper exposure when less light is allowed to strike the sensor. As the amplification of the signal is increased to compensate for less signal, so is the noise.

The way to avoid noise in a photo is to provide more light to the sensor. This can be done by either a) using a wider aperture or b) exposing for a longer period of time. A tripod or other stabilized mount for your camera will allow a much longer shutter time than hand holding the camera.

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Yes, you will get noisier images at higher ISO numbers, and the blue specs are also noise.

The best ISO for an indoor shot depends pretty much on the available light and subject. For a still life, if you can use a tripod, you can use a lower ISO.

But if your subject was a cat, you'd need a faster shutter speed and/or flash, hence reducing the light and maybe requiring a higher ISO.

In other words, the answer to your question is a hearty "it depends."

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