Specify ROI in readBarcode

I have an image with data in text on the image. I expect the same data to be in the barcode at the edge. This should be about 30 decimal digits of data. When I run readBarcode, I get "44083724", format EAN8 and location:

611.5000 40.0000

372.5000 40.0000

264.5000 40.0000

225.0000 40.0000

I think that there are three barcodes at the left of the photo. readBarcode is finding the first and then quitting. I suspect that the location is the end points of the three barcodes.

I ran drawrectangle over the region of the bar codes and got the position 5.0000 0.5000 33.0000 335.5000.

I think the solution is to run readBarcode and specify an ROI for each of the three barcodes on the left edge. I can't seem to do it though. The documentation isn't clear on how to get the ROI from the location or position.

Answer 1

[Abhinav Aravindan]

The "readBarcode" function appears to be recognizing the colour variations near the text as a barcode, rather than the barcode strip on the left side of the image. Plotting the location yields this information.

% Read Image
I = imread("RP 292 H17.png");

% Read Barcode
[msg,detectedFormat,loc] = readBarcode(I);
disp("Barcode format: " + detectedFormat)
disp("Message: " + msg)
disp("Location:") 
disp(loc)

% Plot detected locations
imshow(I)
hold on
plot(loc(1,1), loc(1,2), "r|", "MarkerSize", 25, "LineWidth", 2);
plot(loc(2,1), loc(2,2), "r|", "MarkerSize", 25, "LineWidth", 2);
plot(loc(3,1), loc(3,2), "b|", "MarkerSize", 25, "LineWidth", 2);
plot(loc(4,1), loc(4,2), "b|", "MarkerSize", 25, "LineWidth", 2);
hold off

Output:

It is not clear what the three barcodes on the left strip are, as there does not seem to be any demarcation. However, if you wish to read barcodes in specific regions of the image, you can specify the ROI in the format [x, y, width, height] as an input to the “readBarcode” function. To determine the ROI, you can adjust "loc" accordingly or use “drawrectangle” to interactively select the region and obtain the parameters as follows:

roi = drawrectangle; 
pos = roi.Position; 

For more barcode localization methods, please refer to the link below.

https://www.mathworks.com/help/releases/R2022b/vision/ug/localize-and-read-multiple-barcodes-in-image.html

The following code snippet demonstrates usage of ROI with “readBarcode” :

% Read Image 
I = imread("RP 292 H17.png"); 

% Read Barcode at ROI 
roi = [5.0000 0.5000 33.0000 335.5000]
[msg,detectedFormat,loc] = readBarcode(I, roi); 
disp("Barcode format: " + detectedFormat) 
disp("Message: " + msg) 
disp("Location:")  
disp(loc) 

Output :

The output string being empty suggests that either the barcode might not be valid, or its format may not be compatible with the “readBarcode” function's capabilities. Troubleshooting steps can be found in a related MATLAB Answers query provided below.

https://www.mathworks.com/matlabcentral/answers/733268

Please refer to the below documentation links for more detail:

https://www.mathworks.com/help/releases/R2022b/vision/ref/readbarcode.html

https://www.mathworks.com/help/releases/R2022b/images/ref/drawrectangle.html