How to blur text in image?

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Dominik Mattioli
Dominik Mattioli on 10 Jun 2021
Commented: Johndel Chan on 26 Jan 2022
I'd like to blur only the text found in some images (potentially-sensitive medical information). I'm struggling to remember how to convert bounding boxes into matrix indices, or whether there is a function that does the following.
img = imread('businessCard.png');
imgOCR = ocr( img )
for idx = 1:numel( imgOCR.Words )
bbox = imgOCR.WordBoundingBoxes( idx, : )
subImg = imcrop( img, bbox )
K = medfilt2( subImg )
%%% How to insert K back into img? something like:
% newImg = iminsert( img, bbox, K );

Accepted Answer

Image Analyst
Image Analyst on 10 Jun 2021
Somehow you need to create a mask defining where the text is. Once you got that, blur the entire image, and blur the mask also. Then get the new larger mask and assign the blurred image to the original image in the blurred mask. In short, something like
windowSize = 15; % Whatever.
kernel = ones(windowSize, windowSize) / windowSize^2;
% Blur the mask and the image.
blurredImage = conv2(double(grayimage), kernel, 'same');
blurredMask = conv2(double(mask), kernel, 'same');
newMask = blurredMask > 0; % Mask is now bigger since it got blurred.
% Replace original pixels with blurred pixels.
grayImage(newMask) = blurredImage(newMask);
It would be easier to simply erase the image in the mask than to blur the text and replace it.
grayImage(mask) = 0;
Johndel Chan
Johndel Chan on 26 Jan 2022
@DGM Thanks for the help and I really appreciate the explanation you gave for each solution that you provided! The script now works on my end too. Being partly new to image processing, it seems like I have a lot more to learn about it.

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