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detailed pencil drawing to white background

Oct 9, 2014, 20:46 (This post was last modified: Oct 9, 2014 20:47 by misterroy.)
Post: #1
detailed pencil drawing to white background
My wife is an artist and she likes to work in pencil. The pencil wont scan, but it can be photographed. The background always goes grey. She wants to maintain the detail she can achieve with the pencil, but loose the grey. I have managed before, but it is very hit ans miss as I do not know what I am doing. She draws in pencil, takes a photo in daylight, then I am handed the image to lighten.
Can I have some pointers?
Thanks.
A typical image is below:


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Oct 9, 2014, 22:36
Post: #2
RE: detailed pencil drawing to white background
  • I'm surprised it doesn't scan.... what is the problem? because the photo has plenty of problems:
    • Huge vignetting (dark corners)
    • Some distorsion: zoom to about 3/4 of the zoom range to shoot from as far away as possible (don't go full zoom because this is where vignetting happens (but I think your lady is using the wide-angle side of the range)
    • Shooting in daylight has little purpose for a B&W picture, you just need uniform lighting (lamp sufficiently far from the drawing)
    • Lack of contrast (gray background): this is the camera applying its standard algorithm for people and landscapes to a black and white image. Try to use some manual mode.
    • Excessive image sharpening by the camera firmware: if you zoom on a black line, you will often notice that it is surrounded by two clear lines... these get in the way of any processing you can apply.
    • "Pixel soup" and noise
    All this to say that not scanning also has its problem if all you have is this antique camera. The Canon SD300 is 10 years old technology. You'll get a better picture with a smartphone camera.
  • Otherwise, two simple techniques:
  • The "Levels" tool:
    • You notice in the Histogram that there is a huge peak in the middle: this the gray pixels in the background.
    • Drag the "Whites" handle (far right) to the right sie of the peak
    • Drag the "Blacks" handle (far left) to the left size of the peak
    • Tweak the middle handle for better contrast
    [attachment=4097]
  • The "Curves" tool:
    • Make an S-shaped curve on the left of the peak.
    • Put its top around the middle of the peak
    • Adjust the position of the foot of the S for better contrast
    [attachment=4098]

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Oct 10, 2014, 06:40
Post: #3
RE: detailed pencil drawing to white background
Thankyou, that has to be about the most useful reply I have had on a forum. I have access to an A3 scanner at work and it does a great job of everything except pencil. The detail from the drawing is lost.
thanks again.
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Oct 10, 2014, 07:36
Post: #4
RE: detailed pencil drawing to white background
I'm surprised by this, my personal $100 scanner doesn't. Office scanners have default settings that may not make them ideal for this kind of work, unless you find how to override the settings: they usually have too much contrast (when it's not plain black/white) and the image is produced as a very compressed JPEG. Get a scanner for Christmas, even a cheap entry model will do a better job than your camera.

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Oct 10, 2014, 09:11 (This post was last modified: Oct 10, 2014 11:49 by rich2005.)
Post: #5
RE: detailed pencil drawing to white background
Another way.

You can get a result reasonably easily but you will need an extra plugin G'mic
http://gmic.sourceforge.net/

First some preparation.
1. Convert the mode from RGB to Grayscale http://i.imgur.com/MuhReLZ.jpg
2. Enhance the lines Filters -> Generic -> Erode http://i.imgur.com/lAYzudV.jpg

Then with G'mic
3. Using Repair -> Repair scanned documents. Play with the settings, I increased black level to 50 http://i.imgur.com/m59Wfyf.jpg

4. Gives this. http://i.imgur.com/FbXRqhn.jpg Up to you to repair the edges. Some detail is lost but probably as good as you might get.

edit: another "by rote" possibility

Still a little pre-processing Filter -> Generic -> Erode to firm up the lines

then this script whitebalance.scm http://registry.gimp.org/node/72 using a dark gray foreground colour picked off the image.

One side still has a cast and the edges are to fix, otherwise very straightforward.

screenshot http://i.imgur.com/zGLeaqn.jpg

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