it's a instance: Mat src = imread("linuxconfig_logo.png", IMREAD_COLOR); Mat gray, hsv, ycrcb, j; cvtColor(src, gray, CV_8UC2); cvtColor(src, hsv, CV_8UC3); cvtColor(src, ycrcb, CV_8UC4); imshow("src", src); imshow("gray", gray); imshow("hsv", hsv); imshow("ycrcb", ycrcb); waitKey(0); my sublime replys: terminate called after throwing an instance of 'cv::Exception' what(): OpenCV(4.0.0-pre) /opt/opencv/modules/imgproc/src/color.hpp:253: error: (-215:Assertion failed) VScn::contains(scn) && VDcn::contains(dcn) && VDepth::contains(depth) in function 'CvtHelper'. src has 3 channels and 8bit. Can somebody tell me what'wrong ? i just have learnd it, yesterday. Sry for my EL.