Blotchy, grainy, crunchy, “not clear” – I’ve heard a lot of way’s to describe photos that look, let’s say “less than smooth” when looked at closely.
On a photo or the back of a camera’s LCD screen of course one might not notice grain but under 100% examination one might turn with disgust from what they see. Luckily most of the time views don’t look that close.
Look at a magazine photo under a magnifying glass and you’ll see a lot of “grain” that you don’t notice from a foot away. Same with a billboard.
But if the grain is noticeably visible from a normal viewing distance, it is going to distract from the overall quality of photograph.
What is Grain?
In the days of film photography, light sensitive film was made from crystals of silver nitrate in the case of black and white film or light reactive chemicals in the case of color film.
The finest or smallest grains created the smoothest film negatives but at the cost of a “slower film”. Film with an ASA or speed rating of 50 or 100 would have the finest grains of light sensitive material but would require more exposure. These would typically be considered outdoors films.
Larger crystals would create faster films of say ASA 400 or more noticeable grain in the negatives. Fast films for sports or lower light conditions such as ASA 800 would require less light but the grain would be very noticable.
In digital photography the sensor has a certain number of receptors on it that collect photos. Think of them as little buckets. At lower ISOs such as 100, they work efficiently to collect the photon. The grain is basically these tiny little receptors.
Higher ISOs crank up the voltage to these little buckets and results in spill over causing artifacts, blotches and crunchy spots.
Conditions that create more grain and other degradation of the image include:
- Using high ISO
- Using a camera with a small filter
- Using “digital zoom” instead of optical zoom. Optical zoom uses the lens. Digital zoom is basically multiplying the existing information – so it is making up stuff that isn’t there.
- Underexposed areas will produce blotchy areas such as in the shadows.
You can avoid or reduce grain by making sure there is enough light on your subject so you can use lower ISOs. Also slightly overexposing to make sure the shadow areas have enough light.