Creating a Pencil Image using Gimp 2.6
Gimp is a wonderful and powerful Image manipulation tool, of which I can only but scratch the surface with this or these tutorials. It can manipulate a large variety of Image types and convert them to most any format you may want. Besides the more obvious scale and crop facilities, it also boasts a large number of different filters which extend the Gimp capabilities still further. We will look at at least one such filter in Gimp.
Ensure you have already installed Gimp Version 2.6 it may be possible to accomplish this in the previous version of Gimp we don't know. Gimp 2.6 which at the time of writing this article was the most upto date version available, you should also ensure that this is now running on your Desktop window. With Gimp running, open a new Image that you would like to turn into a Pencil line drawing the image itself can be in colour but the Pencil lines may be rather faint and indistinct. There are many many ways Pencil line drawings can be perfected from, this is only one method, for the Images we strongly urge you to use large sized greater than 2048 x 1400 with a resolution where possible of at least 300 or more, use high definition images where ever possible.
Load your new Image
* Colours >> De-saturate
Turn the loaded picture into monochrome image you can do this using the desaturate option, actually having tried this, this step may not be necessary but as this accepted method works I have decided to include it, you should however take the opportunity to use whatever achieves best the results.
* Filters >> Edge-Detect >> Difference of Gaussians...
This will produce an image similar to the one displayed below, do not worry that the square in the centre is black or adjust of the settings on this run, you can adjust them later if needed. The second image in the series depicts the pencil drawing created this is fainter than we would like but there is something we can do to this. What we can do is to duplicate the existing pencil drawing, to achieve this select the pencil drawing in the layers edit box move your mouse down to the bottom of this edit box and look for the duplicate icon, this has no effect on it's own to the pencil drawing. Be sure to select the top most image on the Layer edit box stack, move your mouse to the Layer mode option "Normal" this will be already selected change this to "Multiply", and you guessed it, it multiplies the two images together, this makes a much stronger image, follow the screen shots to assist you.
As a line drawing the method above works just fine and if this is an example of your completed image we can stop here. Essentially we have a very simple means with which to achieve a line drawing that mimics the original image or photograph, it is slightly more than a three stage process but not that much more. We can now take this image one step further and as you can see from the main picture above we can make the subject a bit more interesting by incorporating both the original image and the line drawing. So how do we merge these two drawings without compromising either image.
Something a bit more fancy
In our Layers edit box we need to flatten our original pencil or line drawing, at the moment the way the image has been left above is that we have two separate but identical images in the Layers edit box, before we take things further we need to condense this down to one image. To flatten this image to just one image you need move your mouse to the Layers edit box if Layers is not yet selected please select it, then right click on the top most image in the stack in this case called background copy and use the right hand mouse button and select from menu flatten image. We then import the same original photograph with which we made the line drawing from into the Layers edit box using drag and drop this places the original photo image above the line drawing. Shifting this image underneath the line drawing could be accomplished by draging the photo image to below the line drawing or as in the example shift the image in the stack by selecting the original photo image and press the down arrow in Layers edit box.
Now we have all the components we need in place within the Layer edit box we can think about how to achieve the blend of these two images to achieve what we want. To manage this unusual look we need to think how we might go about achieving this blend. We could make one layer more transparent than the other and achieve the blend that way, however this has two obvious disadvantages the first and most obvious is that as we make a layer more transparent it not only makes transparent the background but the foreground also, the second disadvantage is that it also effects the whole image not just one part of it. Clearly it is possible to obtain this effect so how do we do it. In order to achieve this effect we need to use a Layer mask on the top most image in the stack then paint with a brush for example in black the parts of the image we wish exposed or in this case transparent.
As we can now see we have not two but three image boxes in the Layer edit box where once there was only two, each of which can be selected as desired. The two image boxes that are on the same layer stack line are the line drawing and the and the layermask itself. We can now go to the tools selector and select a brush tool we must make sure the colour for the brush is blank and white the reason for this is that when the colours are used black provides transparency and white restores the line drawing image back to the way it was for the areas that are coloured using the white. After we have selected the brush it may be necessary to adjust the properties of the brush it's size perhaps should be about 4.75 this is adequate and circle for the brush shape, this It should be stressed that the colours that are selected do not get transfered to any of the images used but the layermask.
Be sure to have black selected as your colour and do not change the image stack after layermask has been added otherwise when you paint on top of the image you will have a nasty black line. Select one corner of your picture and move your brush in that area on top of the main drawing itself the lower photo image is then revealed.
Tip's and Suggestions
* Using levels of grays or even different colours on your 'Layer Mask' will alter the level of transparency when used to paint with on the layermask, so full transparency will be "black", meaning using the black colour will make fully visable the image that is one layer beneath the pencil drawing, using white reverses the effect back to the original line drawing. However by changing the colour to something other than "Black or White" you can filter the level of transparency for the drawings that are merged.
* In this tutorial we have only talked about using the brush which gave us a reasonable level of control, however any of the tools that paint with can used to equal effect. We can also use in conjunction with this the shape tools which are also available on the "ToolBox Dialogue". Create some shapes using rectangles, circles and anything else you fancy to mix and add character to the image you are developing with use of these shape grays and colours.
There are a lot of possibilities using layermask if you can master it, it is a little confusing I know (paint using black and it is transparent, huh!!) but well worth the effort in learning how to use it. This itself has a lot possibilities you could take a photograph of components in your car and make your own manual. All you need do then is put your car back together afterwards. This process is a lot of fun to do and not really that complex it goes a long way to show just how powerful Gimp actually is.