iStockphoto - Stock Photography Training Manual

4.0 Quality Standards

4.6 Noise & Noise Reduction

As lighting conditions become less desirable, photographers adjust by bumping up their ISO to capture more light. Boosting the ISO kicks more electricity through your camera's sensor allowing it to see more light, but this extra electricity heats up your sensor and can introduce pixel discoloration, or noise. These discoloured pixels begin to appear speckled throughout darker areas of your image. The higher the ISO, the warmer the sensor, and the more noise that can appear.

Noise is becoming less and less of an issue as digital cameras and software (RAW converters for example) continue to develop. A typical modern camera body should have no problems with a decent reproduction for an outdoor daylight shot at ISO 400. And it is always better to use a higher ISO and get a proper exposure than to try and fix the exposure later by pushing up the curves.

Curve and contrast editing of these underexposed images has introduced noise even at low ISO settings.

Be careful with night skies and even-toned images. Also watch out of focus and background areas.

Tips:

Use low ISO settings if possible.
If you need to raise your ISO, be sure to nail your exposure on the spot. It's better to use a high ISO to get the right exposure than to try and fix it in post-processing later.
Underexposed shots will most likely introduce some visible noise after editing, especially when bringing up detail in darker areas.
Shoot RAW. The latest RAW editing and conversion programs give you lots of options, as long as the exposure of your original shot is close.

Noise Reduction

If you do end up with visible noise, there are applications and programs out there to help remove it. Always use these carefully and sparingly. Noise reduction programs can be very hard on image detail and if you aren't familiar with the software you can quickly destroy an image and leave it worse than when you started.

Unacceptable:

Extensive noise reduction has killed all the detail in these examples, leaving them soft, smudgy, and plastic looking, with no proper definition.

Original ISO 2500 image with visible noise.

“Luminance” noise reduction, used here, can be too severe. We've lost detail and structure.

“Chrominance” noise reduction works far better, however here some grainy left overs are still visible.

In this example, we gently combined Chrominance and Luminance to remove noise, yet retain detail and definition.

Tips:

First, only use a noise reduction program if you absolutely have to. Modern camera sensors are very good. ISO 400 is beautiful, just make sure your exposure is correct and be careful with your post production. And a little bit of visible noise is preferable to a plastic, damaged de-noised image.
When you have too much visible noise, start the reduction process carefully. Chrominance noise reduction will generally give you a more pleasant, "grainy" look. This is better than Luminance de-noising, which destroys detailed in a particular polished looking way. Generally, some grain is fine.
You may end up using both methods. Proceed carefully, apply small amounts at a time, and observe your detail structure along the way.
Downsizing may improve the overall appearance – you don't always have to work with your camera's maximum native output pixel size. A good looking downsized 8 MP image is better than a lousy over-edited 20 MP image.

Previous | Next

1.0 iStockphoto's Standards

2.0 Account Information

3.0 Image Requirements

4.0 Quality Standards