IMAGE Team - The Pantheon project
The goal is to remove thin and nearly straight lines from image. For example, in the image below, the goal is to remove the horizontal lines that compose the table and the separation lines.
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| The original image. | The result image. |
This method is only convenient for binary and grayscale images because it cannot guarantee to recover the initial colors in case of color images.
The method uses a top-hat with a horizontal linear structuring element to remove the horizontal lines from the resulted image.
The size of the structuring element defines the length of the line to be removed. The top-hat removes the horizontal lines greater than the specified length of the structuring element used in the top hat.
Because, the top-hat yields an image of difference between the closing and the original images, it is necessary afterwards to add the mean value of the input image to recover the initial colors.
Removing vertical lines just needs a vertical linear structuring element instead of a horizontal structuring element.
The black top-hat with a horizontal structuring element of half-size 7 removes the horizontal lines greater than 15 pixels (=2*7+1).
A black top-hat is the difference between the closing (namely erosion of the dilation of the image) and the image. In this application, we use the inverse of the top-hat image since we want negative values for the difference.
Thus the processing is:
g(x,y) = f(x,y) - εH(δH(f(x,y)))
pany2pan bordereau.png bordereau.pan plineardilatation 0 0 7 bordereau.pan tmp1.pan plinearerosion 0 0 7 tmp1.pan bordereau1-1.pan psub bordereau.pan bordereau1-1.pan bordereau1-2.pan |  |
| bordereau1-1.pan: After the closing. |  |
| bordereau1-2.pan: After the difference between the image and its closing. |
To recover the initial grayscale values, the mean value of the closing is added to the previous result. This yields the final result.
pmeanvalue bordereau1-1.pan tmp2.pan paddval tmp2.pan bordereau1-2.pan tmp3.pan pclipvalues 0 255 tmp3.pan bordereau1-2.panbordereau2.pan | |
| bordereau1-2.pan: After mean addition. |
The same plan is used to remove the vertical lines greater than 21 pixels. The structuring element has been changed to a vertical line of size 10.
plineardilatation 90 0 7 bordereau.pan tmp1.pan plinearerosion 90 0 7 tmp1.pan bordereau1-1.pan psub bordereau.pan bordereau1-1.pan bordereau1-2.pan pmeanvalue bordereau1-1.pan tmp2.pan paddval tmp2.pan bordereau1-2.pan tmp3.pan pclipvalues 0 255 tmp3.pan bordereau3.pan ppan2png bordereau3.pan bordereau.png |  |
| bordereau3.pan: After vertical lines removal. |
Pandore script