Image segmentation is the key and important process in the image analysis. In general, thresholding technique is used for the gray level image segmentation and when it comes to apply for the color images, the RGB color image is separated in three gray level planes and then it is applied on these gray level planes or else the color image is directly converted to gray level image and then it is applied on this converted gray level image. This paper addresses the issue of computation time requirement to carry out these three gray level plane image segmentations through the generation of gray level image without using any inbuilt function of tool or platform. The data fusion approach is proposed which is based on the trichromatic coefficients. A single gray level image is formed from the available IR, IG, and IB gray level planes using the trichromatic coefficients. Obtained results are compared on the basis of bilevel and multi-level thresholds. Otsu bilevel threshold of obtained gray level image differs with the Otsu bilevel threshold of converted gray level image by 11%. Obtained gray level image by proposed approach is visually near about similar to converted gray level image. Error between the thresholded images of proposed approach and converted image is less. Obtained multi-level threshold values are close with the multi-level threshold of converted image.