What is ISO ?
In your camera ISO is a key factor ( Shutter speed and Aperture are two others) that is used to control the amount of light in a picture.
Fact about ISO
The acronym ISO stands for “International Organization for Standardization”, that creates various technology and product standards. . However, camera ISO does not directly refer to the organization !
The two film standards namely ASA and DIN were combined into ISO standards in 1974 (later revised for both film and digital photography), they were referred to as one word “ISO” from that point on. Although ISO initially defined only film sensitivity, it was later adopted by digital camera manufacturers with the purpose of maintaining similar brightness levels as film.
What does ISO do ?
When in reference to your digital camera, the ISO is your camera’s sensitivity to light. ISO is displayed in a number like this: 100, 200, or 400. Essentially, when you adjust your ISO, you’re changing your camera’s sensitivity to light (i.e., you brighten or darken your image).
Most of the digital camera sensors have a base ISO value of 100. At a Higher ISO settings, the light falling on the sensor is electronically boosted resulting in a brighter picture. So generally ISO is increased in a low light situation , whereas ISO is ideally kept at low value when there is a good amount of available light.
ISO sensitivity can be set manually by the photographer or automatically by the camera ( Refer your camera manual for the apt settings). The ISO values commonly start from 100. Below are ISO common values examples :
ISO Value in full stops
100 200 400 800 1600 3200 6400
When the ISO value is increased the light falling on the camera sensor electronically boosted to create brighter images. But as the ISO sensitivity increases the noise in the picture also increases.
High end DSLR/Mirrorless have higher ISO ranges extending to 51,200 and 102,400. Also the base ISO is lowered to 32 or 50 in some high end cameras , so as to improve the quality of the image.
How does ISO affect Image Quality ?
When ISO is increased the Image sensor gets heated up due to the electronic boosting of light, which results in a phenomenon of Noise in the sensor. This causes electronically created pixel values, which is Noise in your picture. The image will look grainy and not so appealing. New age cameras offer good noise correction , but always lower ISO settings produce better image quality than one with higher ISO value.
The extended ISO values in the camera are achieved by software simulation of the actual image captured by the sensor. Thus in extended ISO value the image is more of software generated pixels.
ISO Noise can be corrected in Post-production ?
Yes , to some extent the noise in an image can be reduced in post production using various tools and AI apps. However too much noise processing results in artificially created pixels thereby decreasing the natural looks of the image.