A method for tooth region segmentation, executed at least in part on data processing hardware, the method comprising: obtaining an original digital tooth image that has a plurality of color channels; generating an adjusted image by adjusting intensity values of the original digital tooth image to a reduced range between a minimum value and a maximum value, wherein the adjusted image comprises at least a green channel image (Iwgreen), a red channel image (Iwred), and a blue channel image (Iwblue); selecting a channel image from the red, green, and blue channel images, the selected channel image having a higher signal-to-noise ratio than the other two channel images; and when the selected channel image is the green channel image (Iwgreen) or the blue channel image (Iwblue), identifying one or more tooth regions according to a ratio image (IWrgratio) formed by the ratio of the red channel image (Iwred) to the selected channel image; and the identifying one or more tooth regions, comprising: (i) applying a threshold method to the selected channel image by selecting pixel intensity values higher than a predetermined threshold value to generate a threshold selected channel image (Iroi0); (ii) filling one or more holes of the threshold selected channel image (IroiO) to form a processed threshold selected channel image; and (iii) identifying the one or more tooth regions by identifying and removing one or more gum regions determined by color image processing of the ratio image (IWrgratio) from the processed threshold selected channel image. obtaining an original digital tooth image that has a plurality of color channels; generating an adjusted image by adjusting intensity values of the original digital tooth image to a reduced range between a minimum value and a maximum value, wherein the adjusted image comprises at least a green channel image (Iwgreen), a red channel image (Iwred), and a blue channel image (Iwblue); selecting a channel image from the red, green, and blue channel images, the selected channel image having a higher signal-to-noise ratio than the other two channel images; and when the selected channel image is the green channel image (Iwgreen) or the blue channel image (Iwblue), identifying one or more tooth regions according to a ratio image (IWrgratio) formed by the ratio of the red channel image (Iwred) to the selected channel image; and the identifying one or more tooth regions, comprising: (i) applying a threshold method to the selected channel image by selecting pixel intensity values higher than a predetermined threshold value to generate a threshold selected channel image (Iroi0); (ii) filling one or more holes of the threshold selected channel image (IroiO) to form a processed threshold selected channel image; and (iii) identifying the one or more tooth regions by identifying and removing one or more gum regions determined by color image processing of the ratio image (IWrgratio) from the processed threshold selected channel image. (i) applying a threshold method to the selected channel image by selecting pixel intensity values higher than a predetermined threshold value to generate a threshold selected channel image (Iroi0); (ii) filling one or more holes of the threshold selected channel image (IroiO) to form a processed threshold selected channel image; and (iii) identifying the one or more tooth regions by identifying and removing one or more gum regions determined by color image processing of the ratio image (IWrgratio) from the processed threshold selected channel image.