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I scanned a calligraphy using color mode thinking I would capture more details, which I did along with much noise. Now, I would like to remove the background (white) and make it transparent. While doing so, it is difficult to keep some of the details. Appreciate any guidance on how to do this effectively, I have over 60 of these scan to process. Attached one example for illustration purposes.

Please note the details I would like to keep include the thin lines that fades into the supposedly white background. Image reduced for fast upload.

Thanks.enter image description here getting close trying to do this

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  • Hi. Welcome to GDSE. Why do you want to make it transparent? What is it going to be used for?
    – Billy Kerr
    Dec 21, 2019 at 23:58
  • To fill with a different background, like light green, pink, blue, etc. Part of a Calligraphy book.
    – bei
    Dec 22, 2019 at 0:34
  • Then you likely do not need transparency, and only need to change the layer blending mode to multiply to overlay on top of a background image. You can change the white to pure white using a levels or curves or levels adjustment.
    – Billy Kerr
    Dec 22, 2019 at 1:01

1 Answer 1

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  1. If you look at the histogram, the whites are not completely white and the black is not completely black. So you can make a first pass with the Levels tool:

    • In the input area, drag the rightmost handle to the left, slightly past the peak in the histogram that materializes the background color. Anything whiter that the position of the handle will becomes pure white.
    • In that same area, drag the leftmost handle to the right under the first values of the histogram, anything darker will become pure black.

  2. Making the white transparent is easy:

    • add an alpha channel if there is not one already (Layer>Transparency>Add alpha channel)
    • add a layer filled with a test color/pattern under your layer
    • use Color>Color to alpha. In Gimp 2.10, there are two useful sliders to control what happens, and on your calligraphy raising the transparency threshold to 0.1 and decreasing the opacity threshold to 0.6-0.7

enter image description here

PS: I don't know what you want to do with the transparent image, but since your image is black and white, you can overlay it on about anything by putting the layer in Multiply mode. The white being 1., it won't change the image below, and the black being 0. it will set the resulting image to 0., in other words, to black.

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  • Thanks for the prompt reply. Will play around with the recommended instructions in GIMP. Plan to put the calligraphy over a light background, like pink or beige or light blue, etc. But, still would like the details to carry over. Questions: 1) Should I have scanned it using black/white setting with the scanner? or grey-scale? 2) The goal is to capture as much the details as the original, but to replace the white calligraphy paper background with color of choice.
    – bei
    Dec 22, 2019 at 0:19
  • Greyscale is OK. Color won't bring you much, because you would expect the three colors to be equal. You have have to convert to full RGB in Gimp before you can use color on other layers. If the paper is grainy and you want to avoid the texture in the digital image, scan twice, rotating the image 180° for the second scan. Then in Gimp rotate it back, put over the first scan, align them (Difference mode is great of this), and set top to Lighten only. This removes the shadows caused by the slightly on-the-side lighting in the scanner.
    – xenoid
    Dec 22, 2019 at 0:46
  • Thanks again. Would like to keep the texture with black (ink) region for effect. Probably will stick to the color scan for now unless there is a big advantage to re-scan.
    – bei
    Dec 22, 2019 at 0:59

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