Definition and formation of pixel noise
Resolution is used to measure how much of a bitmap image data quantity parameters, usually expressed in pixel.In short, the resolution is the ability
of a camera to interpret images, which is the number of camera image sensor.The maximum resolution is the capability of a camera to interpret images.,
that is the highest number of pixels of the camera.The picture we see iscomposed of multiple pixels(box) as shown in figure 1-4.
（ Figure1） （ Figure 2）
When we enlarge a photograph, we can more or less find some shouldn't exist foreign pixels, this is what we say point noise.
What is the definition of a noise?Noise is how to form ?How to eliminate the noise?In the following, we first explore the process of camera iimaging.
As shown in the above, camera collected the light and transfer to the sensor.Photosensitive material on the sensor prosess the light information and then trasnfer to the DSP(Digital signal prosess).DSP complete the photovoltaic (A/D conversion).However, due to the photosensitive material on thesensor is too sensitive, even in a dark environment, it also can sense some light.As you know, the light human eye can see is limited,.Human can only see the light of wavelength between 380 and 780.So,even in the dark environment, there are a lot of light we can't see. As long as the photosensitive material on the sensor can perceive the light whether or not the human eye can see,itwill converts the light into the signal,.This result the noice inthe image!
How is noise generated? What are the reasons?
1. long exposure time of noisy image
This most appear at night, the darkness of the night sky in the image will become the bright spot.The reason is that the charge-coupled device (CCD charge coupled device)cannot handle a slower shutter speed brought about by the huge workload, which led to some particular pixel out of control.In order to prevent this kind of image noise, in the part of the digital camera is equipped with a known as the function of "noise reduction".If you use the noise reduction function,before recording the image,it will use digital image processing method to eliminate image noise,So it will take a little exrea time before save the image!
2.image of JPEG format compression results the noise
Because of the JPEG image still seem to be very natural after reducing the image size ,you can use special methods to reduce the image data.At this point, it will process the imgage in more than 8 * 8 pixels around as a unit.So especially between the edge in 8 x 8 pixels and the next8 x 8 pixel unit,the combination will not be natural.Image Noise generated by compression of JPEG formats is also known as Mosaic Noise.The higher the compression rate, the more obvious the image noise.Although after the reduction the image, the noise will be looknot to come out,after enlarging,printing and color compensation,noice will be very obvious. This kind of image noise can be solved asmuch as possible through the use of high quality or usingother method except JPEG format to record images.
3. image noisy by the fuzzy filtering
Image noise caused by Fuzzy filter is same as JPEG, which is courseed during the processing of image.Sometimes it is coursed in the process of digital camera internal processing, sometimes in the process of using image retouching software.For small size image, in order to make the imagemore clear and emphasize its color edge, it will produce image noise. Clear processing is the digital camera function of emphasizing on the edge of the image color and image editing software"fuzzy filter (Unsharp Mask)"function. In a different style of digital camera also have some function for emphasising the edge of the whole image color.After processing the image will have other colorline on the outside ofthe edges.
So, how to eliminate the noise?
It is almost impossible.We can only improving the material quality, improve the quality of imagingalgorithm but can not completely eliminate noise.So far, people have developed so me of image quality evaluation method, noise is one of the evaluation of the project.Some camera, mobile phone manufacturer also aware of the importance of image quality, spent big price to do image quality evaluation,from the direction of product improvement.