the process even if rewarding is really simple.

The tutorial require G'MIC installed ...and that you know how load and save images in Gimp
I use also XnView (Free from http://www.xnview.com ) also because has a nice automatic function that work well even in batch and so speed up my workflow...but XnView is not strictly needed and i will explain also how do only with Gimp (if you prefer so )

the goal is to transform QUICKLY a sketch or a old incision as

I

Please see also at original size here https://www.rijksmuseum.nl/en/my/collec ... P-H-1086,0
See at original size is important because show well the sketch, in this case the incision patterns, that the process will transform in a smoother painting



Even if rendering will be slower i suggest you to try this with large images :
just to give a idea most of that here https://www.rijksmuseum.nl/en/mijn/verz ... ix/disegno
(download require login, registration is free ) would work well if used at original size

I will upload my XCF and make a G'MIC "Fav" with the value i used

But the point is not just to copy what i did but make your own
so i invite you to browse for some images, starting old prints from incisions (most here https://www.rijksmuseum.nl/en/mijn/verz ... ix/disegno should be adapt , that side and the google art project are very good places to search for large and high res reproduction)
While you get ready i will start to upload the real tut ,this was the intro

Supposing you don't mind use also Xnview ( That may be used with Wine in Linux and allow to use most PS filters in Linux ...)

1) Be sure the image mode is NOT greyscale but RGB :
in Gimp Image> Image mode > RGB ,if you are browsing with Xnview Image >RGB
(if "RGB" is grayed out, fine, image is already in RGB mode)
Don't forgot this because in "greyscale" mode most of Gimp (or even Xnview) tool and filters would not work as expected or not at all

2) CROP AWAY all the white (or black) border around the image:
that border if present would deceive automatic contrast or level adjustments with well defined white or black area that are external to the area to edit

3) in Xnview Image> Automatic Contrast will most of the time improve the contrast.
If not or if not sufficently you may try also Image> Automatic Level

If you prefer do with gimp are so many alternatives one of most simple COLORS>Level , there click "auto"

So now the skull i chose as example should look so



But what is important is the image texture because is what we will modify and is well visible here at 100% zoom



Now ,paste the image in gimp , open GMIC and change "Output" option (highlighted in the screenshot below )from default to "New Layer", and open Artistic> Dream Smoothing



And we already are close but instead then black we have a not too dark brown
No bad but we want more depth and contrast and some shadows closer to absolute black ...see are no black here



So CTRL+ L to open layer window, there make 2 duplicate of the BG layer (THE ORIGINAL IMAGE ) move one on top, apply a generous gaussian blur (i used 15, again note we are talking of large images, would be MUCH less for little image)change mode to Multiply , multiply because i want also darken, and lower layer opacity



Do the same for the second dup of the original, blur it and move on top
but this time chose "Soft Light" as layer mode , again lower opacity of this layer and



Gmic Presets used : here in this first example the first but in next example in next post i will use also the 2nd
(to use paste on a text editor and save as "gmic_faves" (no quote no extension),whatever are your gmic definition files



sorry the xcf even zipped is 16MB , here the link
https://docs.google.com/file/d/0B3PfZ2r ... sp=sharing

3) a similar technique but adapted to a different drawing, again a BW illustration of a old book derived from a incision "Landschap met het embleem over de Dood en Cupido, Johann Sadeler (I), 1595 - 1600

"

NOW



Just few minutes and i will edit this message to add screenshot link for the xcf and so on ...

EDIT : sorry i must take a break now
BUT here is the XCF that should be almost self explanatory, consider only the visible layers
https://docs.google.com/file/d/0B3PfZ2r ... sp=sharing
I will edit later to add screenshots and few notes

PS

Here i am explaining a simple and almost automatic procedure ;
in this case , for this image , toggle off visibility of the sky using a layermask, and replacing it with a much more smoothed version would enhance the effect, but would also require some manual work

Well i took a break from the break to share this because is even more easy :

This



From



1) Image/Scale Image
break the "chain" scale down only width
i shrink about 10% , more would make the trick too obvious because humans would start to look really too tall, or would require manual corrections (As to crop and paste back the humans figures that can't be stretched so much as buildings or landscape, no without make the trick obvious

2) Stretch the contrast, here is really easy because are no colours to consider, not even intermediate grayscale , is as lineart , lines are gray in the original and should become much darker
I used
Color>Level
( gimp offers so much other ways to do it ..)

3) GMIC
CHANGE "OUTPUT" OPTION from default to "New Layer"
GMIC>DETAILS>Smooth[ anisotropic]
as setting i simply used the "Fav"
DON'T CLICK OK ! instead click APPLY, and do not close gmic or move layers

4)Change gmic filters , again you may use my preset that is for
GMIC>Artistic > Dream Smoothing

5) simply change layer mode of the top layer in Soft Light , in this case i left opacity at 100%

GMIC PRESETS USED (SAME THAT BEFORE; DO NOT INSTALL TWICE ! )



With this process the original layer remain unchanged as BG , and may be used to tone down the effect by simply moving it on the very top and lowering its transparency as needed
( I DIDN'T HERE ! But may be done to make the effect less intense )

XCF https://docs.google.com/file/d/0B3PfZ2r ... sp=sharing

In another topic you may found a very different version :
that illustration are derived from incisions, so works well for engraving effect, as the silver engraved version here
( viewtopic.php?f=11&t=8517&start=0 )

There is 1 step more (= Lighten Effect filter ) but the basic are here

And here i want show another possible interesting effect

Again we start from a good (or at least very large... ) reproduction of a old illustration



as in my last example
1 we apply , WITH GMIC OUTPUT ON "NEW LAYER(s)" the "Anisotropic smooth" preset and the Dream Smoothing presets (always the same , again don't add twice


2 we change mode of upper layer, here i used "Overlay" at full opacity (100) the "{Smooth [anisotropic]}" layer was on top + new layer from visible and ...




No bad , not bad at all
But look better !
And when looking remember that often are the most simple tricks the most effective ...
As example Color>Invert result will look very bluish,
so Color/Level get the "Black" eyedropper of the level tool and click on the darkest blue, then activate the "grey" eyedropper and do the same on the color you want to become close to a middle gray ...Click ok
and



that makes quite a difference with the original ... that again was



Dood van de zonde brengt een nieuw mens tot leven, Dirck Volckertsz Coornhert, 1550

https://www.rijksmuseum.nl/en/my/collec ... I-6544X,12