Method for increasing signal to noise ratio

#1. Field of the Invention

#The present invention relates to a method for increasing signal to noise ratio, and more particularly to a method for increasing signal to noise ratio that can automatically detect saturation output voltage of photosensors via adjusting exposure time or illumination intensity so as to obtain optimum output voltage of the photosensors.

#2. Description of the Related Art

#The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

#FIG. 1 shows a flow chart of the method for increasing signal noise ratio;

#FIG. 2 shows a flow chart of how the method of this invention is utilized in a scanning procedure; and

#It is to be understood and appreciated that the method for increasing signal noise ratio described below do not cover a complete system and method. The present invention can be practiced in conjunction with various software and hardware that are used in the art, and only so much of the commonly practiced components and steps are included herein as are necessary to provide an understanding of the present invention.

#The present invention will be described in detail with reference to the accompanying drawings. It should be noted that the drawings are in greatly simplified form.

#Referring to FIG. 1, a flow chart of the method for increasing signal to noise ratio in accordance with one embodiment of the invention is shown. Under common circumstance, the out voltage of photosensors such as charge coupled devices (CCD) or complemental metal oxide semiconductor sensors is lower than the input voltage of the analog to digital converter (ADC). The method for increasing signal to noise ratio of the invention is used to find out the actual saturation voltage of the photosensors and then increases the output voltage of the photosensors by increasing exposure time tint or lamp illumination to near the actual saturation voltage of the photosensors so that the signal to noise ratio can be increased and image quality can be upgraded. First of all, after step 102, original exposure time tint T0 or original lamp illumination LX0 is set in step 104. Since illumination energy E equals the product of exposure time tint T and lamp illumination L, increasing either exposure time tint T or illumination L will increase illumination energy E. Next in step 106, a white target chart is scanned and the photosensors convert the light which it receives into an electric charge. The magnitude of the charge depend on illumination LX0 (the intensity of the light) and exposure time tint T0 set forth. Then the charges from the photosensors are converted into analog voltages via the analog amplifier. Finally, the analog voltages are digitized to form a maximum data D0 by the analog to digital converter for digital image processing. If a 8 bit analog to digital converter is utilized, data D0 is from 0 to 255. In step 108, maximum data D0 is compared to 255 if a 8 bit analog to digital converter is utilized. If maximum data D0 is smaller than 255, then exposure time tint Tn or lamp illumination LXn should be increased and the white target chart is scanned again in step 110. The magnitude of the charge now depends on illumination LXn+1 and exposure time tint Tn+1. Then the charges from the photosensors are converted into analog voltages via the analog amplifier. Finally, the analog voltages are digitized to form a maximum data Dn+1 by the analog to digital converter for digital image processing. The maximum data Dn+1 is then compared to the previous maximum data Dn (starting from D0) in step 112. If the maximum data Dn+1 is not larger than the previous maximum data Dn, that means that the output voltage of the photosensors has been saturated and exposure time tint Tn or illumination LXn generating the maximum data Dn is saved in step 114. On the contrary, if the maximum data Dn+1 is larger than the previous maximum data Dn, that means that the output voltage of the photosensors has not been saturated and the process goes back step 110 until the output voltage of the photosensors is saturated.