Python - 删除来自图像边界的黑色像素

Question

I am very new to Image processing and I am trying to cleanse pictures similar to picture 1 of the Black Pixels originating from the border of the Image.

The Images are clipped Characters from a PDF which I try to process with tesseract to retieve the character. I already searched in Stackoverflow for answers, but only found resolutions to get rid of black borders. I need to overwrite all the black pixels from the corners with white pixels, so tesseract can correctly recognize the character.

I cannot alter the Bounding Boxes used to clip the Characters, since the characters are centered in different ares of the BoundingBox and if i Cut the BoundingBox, i would cut some Characters like seen below

My first guess would have been to recursively track down pixels with a certain threshhold of black in them, but I am scared of computing time in that case and wouldn't really know where and how to start, except for using two two-dimensional arrays, one with the pixels, and one with an indicator whether i already worked on that pixel or not.

Help would be greatly appreciated.

Edit: some more pictures of cases, where black pixels from the edge need to be cleared:

Edit: Code-Snippet to create Border Image:

    @staticmethod
    def __get_border_image(image: Image) -> Image:
        data = numpy.asarray(image)

        border = cv2.copyMakeBorder(data, top=5, bottom=5, left=5, right=5, borderType=cv2.BORDER_CONSTANT)

        return Image.fromarray(border)

Answer 1

Try like this:

• artificially add a 1px wide black border all around the edge
• flood-fill with white all black pixels starting at top-left corner
• remove the 1px border from the first step (if necessary)

The point of adding the border is to allow the white to "flow" all around all edges of the image and reach any black items touching the edge.