Research And Realization Of Auto White Balance Algorithm For Digital Camera

3-A algorithm （automatic focus, automatic exposure, automatic white balance）has been the core content for study since the digital camera has been invented.These papers mainly focus on the research of the algorithm of automatic whitebalance and try to achieve this. Color constancy of human vision is that peopleperceive the relatively constant color for a same object under different light sources.However, the photos taken by digital camera are in shades of red under low colortemperature, while they are in shades of blue under high color temperature,adjustments to white balance must be done in order to fix this phenomenon. Takenliterally, white balance is the global adjustment of the intensities of the colors. Nomatter which kind of color temperature of the light sources the white object is under,the color of the white object can be reversed into the original white.Under the research of existing achievement of automatic white balance algorithm,to overcome the failure of gray world method in the scene with single color and thefailure of perfect reflector theory when the high luminance pixel exists in image, thispaper provide a improved automatic white balance algorithm based on the judgmentof the color temperature. First, in order to make calculation more conveniently and getthe properties of light sources, divide the whole image into16*16macro blocks. Then,according to the provided limits of R/G and B/G under different color temperature todistinguish the different light source. If there are over50macro blocks belongs to onelight source, this light source is marked as100, and the other conditions are countedby function relationship. Misjudgment may happen if the light sources only estimatedby the limits of R/G and B/G. erroneous judgment of light source usually takeluminance as criterion; the erroneous judgment also has corresponding principle ofdeduction. The type of light source of the whole is judging by the final criterion, thelight source of the whole image got the highest point. Finally, calculate the gain of thewhite balance. According to Grey world theory, under one certain light source, thethree primary colors red, blue, green get the same gray value, set the gain of the greenchannel as256, calculate the gain of white balance of Rgain and Bgain.To assess adjustable effects of the white balance algorithm, testify this algorithmby transplanting it on the hardware platform based on NT96211. Adopted bothobjective and subjective method to estimate this white balance algorithm. The subjective method is using human eyes to observe pictures. The objective method is toanalyze the effect of white balance algorithm by using employed data of digital imageprocessing software. This two evaluations show that the white balance algorithm putforward by this paper improves at a large extent compared to typical algorithm. In themeantime, the main difference between this algorithm and general algorithm appliedin digital camera is that the parameters of white balance of this algorithm are obtainedby analyzing the data of current frame. The parameters of white balance used in thisalgorithm are based on the data of last frame. Hence, this advantage is more suitablein infrared monitor products.