MATLAB: Pixels to inch conversion

calibrationimage acquisitionimage analysisImage Processing Toolboxspatial calibration

Hello everyone, I need to convert the number of pixels into inches(cm)…I know the calculation but if the image is taken as a photograph, based on the camera distance number of pixels are varied…Then what is the relationship between number of pixels and camera focal length…Thanks in advace …

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See my spatial calibration demo, attached. It lets you specify some known distance in the image and then make measurements based off of that.

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MATLAB: Determination of stereo camera world coordinates with respect to calibration target

Matt's is almost correct. The extrinsics R and t represent the transformation from the world coordinates into camera's coordinates. So t is not the camera center. You have to rotate as well. The only problem with Matt's solution is that it does not follow the vector-matrix multiplication convention used by the Computer Vision System Toolbox. The camera center in the world coordinates is

c = -t * R';

because t is a row vector.

Also, you do not have to use one of your calibration images. You can calibrate your cameras and then take a new picture of a checkerboard, and use the extrinsics function to compute the R and t relative to that board. See this example.

MATLAB: Trasform focal length from pixel to world unit

During camera calibration you can only calculate the ratio of the focal length to the pixel size, i. e. the focal length in pixels. You cannot calculate the focal length in world units and the pixel size separately. The best you can do is look up the pixel size from the manufacturer's spec, and then calculate the focal length in millimeters.

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MATLAB: Determination of stereo camera world coordinates with respect to calibration target

MATLAB: Trasform focal length from pixel to world unit

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