some special effects

[Image Processing]

Hi, I am learning image proceesing nowadays. And I find that GIMP is really a nice 
place to visit. 

I have several questions. I like to implement some special effects by myself, such as 
'Colored Pencil', 'Chalk & Charcoal' in Adobe Photoshop. But I don't know how to do. 
Could anybody give me some advice about how to do? Thanks a lot!

Best Regards,

Bam


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