Scanning pencil drawings

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Sgt. Groovy
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Scanning pencil drawings

Post by Sgt. Groovy »

Does anyone know how to get good scans out of pencil drawings, or have some references? I've googled up and down the net but I haven't found a tutorial.

By good scans, I mean getting the different shades of grey right. The upper picture below is the best I have managed so far, but if you compare to the lower one, which is a digital photograph of the same drawing, the scan misses the lighter shades of gray. I can adjust the scanner settings to get the lighter shades out, but not without the darker parts getting too dark and glogging up. I've tried every setting of the scanner, and all kinds of post-prosessing, but the best way I can get a pencil drawing to computer is digital camera. The problems with camera are that the maximum practical resolution is about 160dpi, I have to wait a sunny day to get enough light and they don't come out quite sharp.

What I would like to do is make images by first making a pencil greytone, where I can get sophisticated shading done fast and easily, and colour it on the computer.
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erminecomb.png
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BloodIssyl
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Post by BloodIssyl »

yeah, i dunno, i just live with the dissapearing of the lighter shades.

That drawing is INCREDIBLE though.
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vonHalenbach
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Post by vonHalenbach »

Maybe you can make a HDR-Photo out of your scanned images. You simply scan once with setting dark and once with setting bright. Then you have to merge them together with gimp (dont ask me how google for HDR image ). This technike is used by lowlight-photographers to get the best out of their pictures.
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Post by Shadow »

I gave up instead I do it all digital now.
Wheter I could see the pores of the paper or I lost the shading.

Nice drawing though.
... all romantics meet the same fate someday
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Sgt. Groovy
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Post by Sgt. Groovy »

Maybe you can make a HDR-Photo out of your scanned images. You simply scan once with setting dark and once with setting bright. Then you have to merge them together with gimp (dont ask me how google for HDR image ).
Thanks for the tip, this is basically the same problem. There is a GIMP plugin to extend dynamic range by merging a light and dark exposed version. It works, but not good enough for me, and there are too few parametres to change. I tried to blend on my own, by simply overlaying the darker version on the lighter one with the darken filter and 50% opacity. The result (image below) is better than my latest attempt with scanner, but not as good yet as the photo.

Mathematically, it should be a weighted average of the two luminosity values, with the weight factor determined by per pixel basis: closer to the darker value in the lighter (above midgray) areas, and closer to the lighter one in the darker areas. If I can't figure out a way to do this with the standard filters, I'm going to have to write my own plugin (I've made a GIMP plugin before in Python, it's not terribly difficult).

Another solution would be to not use white paper. I have a hunch that the poor graytone resolution in the lighter end is because the white paper just scatters too much light back and drowns the light grey signal. I bought some gray paper, and according to my first trial it seems I'm right. The scan looks pretty much like the real thing. I still get the full tonal range by using a white pencil (out of a colour pencil set) to make the highligts. The drawback is that on the grey paper the texture of the paper becomes more visible.
Wheter I could see the pores of the paper or I lost the shading.
The problems of porous or granular material can be alleviated by scanning first in higher resolution, applying a small Gaussian blur, and then scaling down to the desired resolution.
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erminenew.png
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Sgt. Groovy
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Post by Sgt. Groovy »

Whoah, it appears there is another HDR plugin for GIMP, using three exposure levels. Have to try that too.
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Sgt. Groovy
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Post by Sgt. Groovy »

OK, having played around with both of the HDR tools, I must conclude that the digital camera is still my best option for drawings on white paper. The reason is that my scanner simply can't see the lightest shades of grey, even with the lowest gamma setting, and no amount of dynamic range extension can bring out shades that simply aren't there in the original images.

Nevertheless, I have learned a number of useful things with this exercise, and will make a tutorial about it. I'll also make a tutorial about "scanning" with a camera, as there are a whole bunch of tricks to that as well.
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Sgt. Groovy
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Post by Sgt. Groovy »

Feh, colour me dumb. Actually, I can set the exposure low enough to get the lighter shades out of the drawing. The problem before was, that I was only changing the gamma and brightness values of the "enhancement" settings, which only process the data after it has been scanned. The setting for changing the brightness of the actual scanning head light source is in the another window of Xsane, titled "standard options" and the changes won't be seen on the preview until the "acquire preview" button is pressed again.

The image below has been scanned in three brightness settings, -2, 0 and 1, and combined with the "Python-fu -> Render -> HDR tone mapping" plugin (must be separately installed). It is now at least as good if not better than the photograph, and with a little trial and error it might get even better.
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Sgt. Groovy
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Post by Sgt. Groovy »

Tiedäthän kuinka pelataan.
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Tiedäthän, solmu kravatin, se kantaa niin synnit
kuin syntien tekijätkin.
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vonHalenbach
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Post by vonHalenbach »

Sgt. Groovy wrote:Tutorial up.
Thank you for your enlightening tutorial. This will help many more artists, to get their drawings into their computer with less loss and when they understood, that this technic is not limited to the scanner, they will start to make impressive photos with their digital camera. :)

In some good digital cameras is a funktion integrated to make many photos with different settings at once. This is called "bracketing". With bracketing you can shoot 3 pictures with different focus or different exposure settings in a row. Sadly, only expensive cameras have bracketing available.
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