What is Grain, noise and pixel density?
The digital equivalent of film grain is noise, and you will find noise in every image captured by a digital camera. Noise is generated when heat from the electronics free electrons from the image sensor; these are ‘thermal electrons. The smaller the CCD sensor in the camera or the higher the ISO, the more likely you are to have large amounts of noise. When the size of the sensor remains the same, but the megapixel count keeps climbing, with more and more transistors sitting side by side there is less room for excess heat to escape and this can result in increased noise being generated. This can be an issue with some compact digital cameras as some manufacturers try to keep their size small, while increasing megapixel count and adding features. The higher the sensitivity of the CCD (the ISO) the more noise it generates.
Lots of cameras have built-in noise reduction algorithms that generally are very capable of
reducing the noise. You can also remove most noise in post-production with built-in noise reduction functions or by using specialized plug-ins. The noise generated also differs greatly from camera to camera but generally you will find more noise at high ISOs and with long exposures
Optical and digital zoom
With optical zoom, the lens elements move around to zoom in or out by changing focal length. A digital zoom combines optical zoom with a technology called ‘interpolation’ or ‘re-sampling’ to provide new levels of zoom. When you use digital zoom, and you hit the outer limit of the optical zoom area, the camera then starts its digital zoom software which crops in on the detail you’re zooming in on. The result is an image with a crop of the maximum optical zoom image, which has been ‘interpolated’ back to full size. This in most cases results in the degradation of the overall image quality by increased pixelation and muddiness. You should only use digital zoom under special circumstances, such as when it is impossible to move any closer to the subject. On most cameras you can disable this feature, so you don’t use it accidentally.
Image stabilizer
Another feature often mentioned when digital cameras are advertised is optical image stabilization (OIS). You may have seen its effects without realizing it, as more and more cameras now come with image stabilization. If you are photographing in low light conditions and are unable to use flash, the resulting images may show signs of camera shake. Optical image stabilization is designed to counteract this, enabling you to take sharp pictures in low light.
The camera achieves this by a moving element in the lens compensating for small movements (shake) detected by solid state positional devices.
Bit depth
A bit is essentially the smallest unit of data: It is either 0 or 1, black or white, on or off. 8 bits is a byte and can therefore represent 256 different states, 2^8th. To make matters more complicated, 8 bits is sometimes also referred to as 24 bit, as it is a composite of red, green and blue.
Most of the digital world operates in 8 bit – your monitor and printer for instance. If you are shooting in the RAW file format newer cameras can produce images in either 12, 14 or 16 bit depending on the camera used.