MATLAB: How to convert pixel size to inches

pixels

I have an image of my experimental specimen. I know the dimensions of my specimen. I have taken a picture of my specimen. Now, how can I convert pixel information from the image to get the dimensions of my specimen? Basically, I can measure pixel distance and want to correlate to real life dimensions.

Best Answer

You need to have an object of known length, such as a ruler or some other calibration standard, in your image. Then measure its length to get a calibration factor with units of centimeters (or whatever) per pixel. Then when you have some other length, just simply multiply by that calibration factor to get a length in units of centimeters. If you have an area, multiply by the square of that factor to get the area in cm^2.

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MATLAB: Function estimateWorldCameraPose() or extrinsics() for fisheyeParameters is missing. Is it possible to change these functions for fisheye

fisheyeIntrinsics can't be used directly. Instead, you can use undistortFisheyeImage function to produce both undistorted image for further processing and a "virtual perspective" camera intrinsics. See syntax which returns "camIntrinsics"

The new camIntrinsics can then be used in workflows involving a pinhole camera. It is a virtual pinhole camera created from the original fisheye camera. This new intrinsics object (non-fisheye) can then be fed into estimateWorldCameraPose.

MATLAB: Convert unorganized point cloud (MX3) to organized point cloud (MXNX3)

You do not need to convert a pointCloud to organized form to use the pcfitplane function.

Here is an example:

% Read an unorganized point cloud
ptCloud = pcread('teapot.ply');
% The point cloud is unorganized, since Location property is M-by-3
disp(size(ptCloud.Location))
% Use pcfitplane
maxDistance     = 0.5;
referenceVector = [0 0 1];
model = pcfitplane(ptCloud, maxDistance, referenceVector)
figure
pcshow(ptCloud)
hold on
plot(model)

If you are getting an error, could you please send reproduction steps and the release of MATLAB you are using (use the ver command).

Best Answer

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MATLAB: Convert unorganized point cloud (MX3) to organized point cloud (MXNX3)

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MATLAB: Function estimateWorldCameraPose() or extrinsics() for fisheyeParameters is missing. Is it possible to change these functions for fisheye