John Davidson

Message:

I've been trying to use Imagick to turn PDF files in my PHP application into PNGs so that I can get Tesseract OCR's PHP library to scan only handwritten text in the documents. The handwritten text areas are surrounded by a black border in the documents, and there's a chance that they could be slightly tilted since some of the PDFs are scanned.

Is there any way that I can use Imagick to create images of only the bordered boxes from the PDFs? I've tried looking at the Imagick docs and tried using despeckleImage() and then trimImage(), but I was only able to trim a little bit due to some fuzz pixels in the image.

The box with the handwritten text is the one I want to get an image of so that I can scan that text in it. This imgur link has both scans I've been working with. The first one has no fuzz at all, but the second one is a scan with fuzz. I'm not sure how to even approach the problem since there are so many functions in the library, so if you guys have any ideas it would be much appreciated.

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My Answer:
One approach you could take is to use the Imagick library to detect the black border surrounding the handwritten text areas in the PDFs. Here's a general outline of how you could do this:

1. Convert the PDF file to an image using Imagick.
2. Use the getImageHistogram() method to get a histogram of the image colors.
3. Loop through the histogram to find the color that corresponds to the black border.
4. Use the floodFillPaintImage() method to fill the area surrounded by the black border with a different color.
5. Use the trimImage() method to trim the image to the area surrounded by the black border.

Here's some sample code to get you started:

php
// Load the PDF file
$pdf = new Imagick('path/to/your/pdf/file.pdf');

// Convert the PDF to an image
$pdf->setImageFormat('png');
$pdf->writeImage('path/to/output/image.png');

// Load the image
$image = new Imagick('path/to/output/image.png');

// Get the image histogram
$histogram = $image->getImageHistogram();

// Find the color corresponding to the black border
$blackColor = null;
foreach ($histogram as $pixel) {
$color = $pixel->getColor();
if ($color['r'] == 0 && $color['g'] == 0 && $color['b'] == 0) {
$blackColor = $color;
break;
}
}

// Fill the area surrounded by the black border with a different color
$image->floodFillPaintImage($blackColor, 0, $blackColor, 0, 0, false);

// Trim the image to the area surrounded by the black border
$image->trimImage(0);

// Save the trimmed image
$image->writeImage('path/to/output/trimmed_image.png');


This is just a starting point and may need to be adjusted based on the specific characteristics of your PDF files. You may need to experiment with different methods and parameters to get the desired result.