how to crop an image id-card only ..?

how to crop an image id-card only ..? using regionprops.

[Malta]

help me....!!

Answer 1

[Walter Roberson]

First you threshold based on brightness. regionprops() and look for the one with the largest Area. Fill the inside of the pixel boundaries for that. The result will be a mask that you can use to extract the ID card from the color image.

[Malta]

Can you give an example of source code regionprops to my problem ..?

[Walter Roberson]

regioninfo = regionprops(ThresholdedArray, 'Area');
[maxarea, maxidx] = max([regioninfo.Area]);

The blob #maxidx is now the largest region.

[Malta]

what if the id-card that I use is not fixed ..?

[Image Analyst]

If by fixed you mean always in the same location, it does not matter. regionprops() will find the blobs in the binary or labeled image regardless of where they are locataed in the image, or how they are oriented.

[Walter Roberson]

And also regardless of if they are a constant size.

What you do need to worry about is the thresholding method, if they can be different colors. You are, for example, likely to have problems with a pure black ID-card that lights up in black with black letters.

Answer 2

[Image Analyst]

Get a monochrome image, for example by looking for white, if the cards are always white. Then threshold and find the largest white blob. This is done in my Image Segmentation Tutorial: http://www.mathworks.com/matlabcentral/fileexchange/25157-image-segmentation-tutorial-blobsdemo

If you want to get a perfect rectangle from the blob, get the filled object and then use http://www.mathworks.com/matlabcentral/fileexchange/34767-a-suite-of-minimal-bounding-objects