Image noise is random variation of brightness or color information in images. Image noise is to some an enemy even a source of stress and to others it just doesn’t matter since the content of the image is king. Multiple noise reduction software such as Neat image, Denoise, Noise Ninja exist to control this image variation at a cost of sharpness, saturation and other degradation of the image.
What is ISO?
ISO is an international standard of sensitivity to light. Your camera’s sensor “sees” more light as the number goes higher. You will see more light at ISO 3200 then at ISO 100. The dark side is the fact that you will get more digital noise in your images at higher ISO. I don’t pay much attention to digital noise since I want my image. The audience will see the emotion or moment rather than the digital noise. You also have to be careful since higher ISO will cause a softer (not as precise and defined) looking images.
Why would you use a higher ISO?
You need a higher ISO to “see” more light inside and during sporting events to freeze subjects movements. Higher ISO in possible because the electrical current that passes through your sensor is higher and make the sensor more sensitive to light. You need to keep your shutter speed at a minimum of 1/125th of a second to proper achieve portraits. For landscape and architectural photography, I would strongly suggest to use a tripodand use longer exposition.
How can you hide digital noise?
You can either use software to reduce digital noise if it’s unacceptable. Adobe LightRoom 5 is a great software for file editing and noise reduction.
I have my own trick that I have developed over my years of experience of shooting.
To hide digital noise, insure that you use proper white balance and that you over expose your images by at least 1/3 of a stop. Improper white balance can cause you to underexpose your images by a full stop. Overexposing the images by a small amount gives you the latitude to bring the exposure down in Lightroom or Photoshop. When you underexposed your image, you’re adding image noise when adding exposure in software. With this technique I am confortable shooting images at 6,400 ISO without having serious image degradation.
Both the following images have been taken at ISO 2500.
You need to learn about your best ISO to use the performance of your sensor to it’s limit. In a Canon DLSR you want to use 160, 320, 640, 1250, 2500, 5000, 10000, etc. For a Nikon DSLR, you want to use 200, 400, 800, 1600, 3200, 6400, 12800, etc.