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 is composed of multiple

pixels(box) as shown in figure 1-4.

                     （ Figure1）                                                                  （ Figure 2）

          
                       （ Figure 3）                                                                （ Figure 4）

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 the

sensor 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,it

will converts the light into the signal,.This result the noice in the 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 next

8 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 look not to come

out,after enlarging,printing and color compensation,noice will be very obvious. This kind of  image

noise can be solved as much 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 image

more 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 teh whole image color.After processing the image will have other color

line on the outside of the edges.

So, how to eliminate the noise?

It is almost impossible.We can only improving the material quality, improve the quality of imaging

algorithm but can not completely eliminate noise.So far, people have developed some 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.