How to convert from CV_16S to CV_8U || CV_16U || CV_32F? cvtColor assertion failed

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Hi,

I am having trouble converting a Mat to gray scale using the following (more details below)

cv::cvtColor(result, gray, COLOR_BGR2GRAY);

result is a Mat. It is the output of image stitching (from the sample: https://github.com/Itseez/opencv/blob...):

Mat result, result_mask; blender->blend(result, result_mask);

result Mat properties:

• result.rows 2310
• result.cols 5545
• result.type 19
• result.channel 3
• result.depth 3

I am trying to convert this Mat result to grayscale as a first step in another cropping function:

cv::Mat gray;
cv::cvtColor(result, gray, COLOR_BGR2GRAY);

but fails at the assertion on line "cv::cvtColor(result, gray, COLOR_BGR2GRAY);":

OpenCV Error: Assertion failed (depth == CV_8U || depth == CV_16U || depth == CV_32F) in cv::cvtColor, file C:\builds\master_PackSlave-win32-vc12-shared\opencv\modules\imgproc\src\color.cpp, line 7343

If I imwrite the result Mat above, and imread it back in like so:

imwrite(result_name, result);
Mat toCrop = imread(result_name, CV_LOAD_IMAGE_COLOR);
cv::Mat gray;
cv::cvtColor(toCrop, gray, COLOR_BGR2GRAY);

Then there are no errors

toCrop Mat properties after reading back in are:

• toCrop.rows 2310
• toCrop.cols 5545
• toCrop.type 16
• toCrop.channel 3
• toCrop.depth 0

Any ideas on how to get this working without writing and reading, using the original Mat result to convert to grayscale? I believe the depth is the issue. The result is I've been searching how to do a conversion of the depth but no progress..

Thanks for your support