关于评价彩色图像质量的相关定义，如常用的MSE和PSNR，与灰度图像稍有区别，在图像的滤波、加密恢复等可以用得到。-Associated definitions on the evaluation of the color image quality, such as the commonly used MSE and PSNR slight difference with the grayscale image in the image filtering, encryption can be

If we know some properties of the image, than thresholding process only needs to ensure this property is satisfied. In a printed text image, if we know the ratio of area between the sheet and character, then we can choose satisfied threshold value