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I have seen a lot of very different tutorials about how to remove blue lines from a scanned drawing. So I ask myself what is the best way in term of simplicity and quality to do this in Photoshop (CS3 and above).

And also, is the choice of the blue color really the best, or there are other better colors in order to obtain a clean final drawing with the sole black lines?

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  • @Joonas, can you tell me a bit more what you're thinking of? Nov 25 '21 at 14:07
  • @PetaspeedBeaver, I dont know how to answer that. It's a link to basically the the same answer as Cai's answer in this post. The idea, if I were to elaborate it a bit, is that if you sketch with say a blue pencil and then do cleaner lines on top of that with any other color, you can use B&W adjustment to turn blue color to white super effortlessly. If you do line art with the same color as sketch, it's way harder to get rid of the sketch lines as the only thing you have to go on is that sketch lines are probably lighter in color.
    – Joonas
    Nov 25 '21 at 14:19
  • @Joonas, Haha, sorry for the weird question ... and great thanks for trying to explain it to me. The reason for me asking was that I missed the important fact that what you wrote was a LINK TO A QUESTION :) Nov 25 '21 at 20:18
  • @PetaspeedBeaver :)
    – Joonas
    Nov 25 '21 at 20:23
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To remove blue sketch-lines in Photoshop, follow these steps:

Source: https://oomizuao.deviantart.com/art/removing-blue-sketch-lines-251501190

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    If that image came from oomizuao.deviantart.com/art/… and you're not oomizuao, you should probably credit your source Jun 21 '13 at 15:20
  • When I read this I keep saying to myself that there must be a simpler way to do this and still achieve good results ... :) Nov 1 '21 at 20:49
  • Please edit this post to prevent link rot and respect author's rights.
    – curious
    Nov 2 '21 at 15:33
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Another solution:

Image > Adjustments > Black & White.

Make colors blue and cyan as clear as you want until the blue lines disappear.

And that´s it.

(This solution works only on RGB mode.)

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I've found the following method to be simple and effective:

  1. Decompose the image so that each channel is on its own layer.
  2. Discard all layers except the blue one, where the blue pencil will be almost invisible.
  3. Adjust threshold, curves or levels until the last residues of the blue pencil is gone.

Choice of pencil: Note that this method depends on that the pencil used has a pigmentation that almost only affects the blue component of the RGB image. You can try different pencils, and will notice that pencils with a little red in them (the ones that draw towards violet) will not work so good. Also make sure to always make you lines very light.

An example: The image below samples a few blue pens.

enter image description here

It's then decomposed in Gimp using Colours--Components--Decompose, and the R and G components are scrapped, leaving only the Blue: enter image description here

And made black and white with Colours--Threshold. It can then be converted to a 2-bit (black and white) image if you want to use an indexed image format to save it.

enter image description here

Note that the pencil that has some red in it doesn't work good.

And also, is the choice of the blue color really the best, or there are other better colors in order to obtain a clean final drawing with the sole black lines?

If you're going to use my method, you have to use a pencil containing either a pure red, green or blue pigment. Of these colors, I'd suggest blue, since it's a color that tends to not draw you attention too much. Blue is the color often used in landscape painting to show something is in a distance for example, and it's commonly used in film lighting to make backgrounds less prominent in the image. I think blue is a good choice of color for many reasong.

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