Once I was searching for GIMP tutorials to convert a photograph to a pencil sketch. Almost all tutorials I found used same technique which I think can be roughly summarized as finding edges in the image and inverting the colors. Though the results were fine they seemed to lack something, and then I thought of adding the diagonal pencil strokes.

I used GIMP 2.6.2 and a 1024x768 sized image.

Original Image:


Final Image:


Following are the steps (including the ones I learned from other tutorials)

1] Open the image in GIMP

2] Duplicate the layer

3] Gaussian blur the top layer. I used the blur radius as 5 pixels.

5] Invert colors of the blurred layer, and set its transparency to 50%.

6] You should have something like this.

 
7] Merge down the top layer.

8] Open colors | Levels, set the minimum and maximum input levels as 100 and 155 as below.


 
9] Desaturate the layer

10] Open Colors | Levels, adjust the input levels so as to get something similar to the following


 
11] Now Duplicate this layer. Hide the top layer and select the second one.

12] Select Filters | Blur | Motion Blur. Select blur type as Linear, length as 10 angle as 135. Repeat motion blur with angle changed to 315. You should get something as:



13] Unhide the first layer set its transparency to 20%. Merge down the top layer with the blurred layer.



14] Select Colors | Contrast. Increase the contrast slowly till image looks more like a pencil sketch. I increased the contrast to a value of 15, to get the following result


 
15] Now we need to add some more random pencil strokes. Add a new transparent layer of size 512x384 i.e. of half width and height of the image.

16] Select Fileters | Noise | Hurl. Select a random seed. Set randomization% to 10 and repeat to 1. This should add some random dots to the layer.

 
17] Select Layer | Scale layer. Scale the layer to image size select interpolation as cubic. Move the layer if necessary to overlap the image correctly. You will have something like this



18] Select Colors | brightness and Contrast. Set Brightness to minimum and Contrast to maximum.

19] Now again apply motion blur on this layer as previously. But keep the length as 20.

20] Again merge down the blurred layer.

21] Now, Select Colors | Brightness-Contrast. Reduce the brightness and increase the contrast to get something like this:

 
22] Now you can apply canvas from Filters | Artistic | Apply Canvas, to give it a more realistic look. Here is the final image that I got after applying canvas:

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