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question of reading pixel

asked 2018-01-16 03:09:20 -0500

Weifa Gan gravatar image

when reading pixel of image,using this sentence: (unsigned int)img_pyr2.at<uchar>(y, x) I don't know that why use the data type,uchar. when i changed uchar to int,it will be error;

i just learn opencv,pleace help me to understand. Thank you.

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answered 2018-01-16 03:43:33 -0500

kbarni gravatar image

For each image type you have the according data type: uchar for CV_8U, Vec3b for CV_8UC3, ushort for CV_16U, int for CV_32S, float for CV_32F etc.

Always use the according data type:

Mat image(100,100,CV_8UC1);
uchar pixel=image.at<uchar>(10,10);

(you don't need a second type cast: pixel=(uchar)img.at<uchar>(10,10);)

The pixel access in OpenCV is quite well explained in the docs.

It's also good to learn the pointer (line) access.

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thanks your help

Weifa Gan gravatar imageWeifa Gan ( 2018-01-16 05:43:29 -0500 )edit
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answered 2018-01-16 03:42:18 -0500

VxW gravatar image

you also have to learn C++, see e.g. C++ Templates

<uchar> is a template parameter and means that img_pyr2 must be of type uchar

if you would like to convert an uchar image to int you should use img_pyr2.convertTo(img_pyr_int, CV_32S);. Afterwards you can access the pixels via img_py_int.at<int>(y, x)

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thank you very much!

Weifa Gan gravatar imageWeifa Gan ( 2018-01-16 05:42:03 -0500 )edit
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Asked: 2018-01-16 03:09:20 -0500

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Last updated: Jan 16 '18