I've been trying to draw some shadows for this month's TIF project and been quite unable to get the distortion to look right. I have previously tried to work with images in Corel Photopaint but have never had much success using the Edge finding tool in order to grab an outline.
However, recalling the experiments in colour replacement I did last month it occurred to me that I could create a black and white image in GIMP from which I could obtain an outline. (Similar tools are available in Photoshop but they may be listed under different menus.) Here's how I went about it.
This is my starting image, already cropped from a bigger picture:
First I indexed the image Image>Mode Indexed and chose to limit the palette to 6 colours:
Then beginning with the lightest shade I edited each colour to white until only the darkest area remained which was edited to black. (Sometimes it's best to edit more than one colour to black depending on the shading in the original image.)
This left a fuzzy image with unwanted areas of black in the foregound:
A quick whizz round with a paintbrush cleaned up the image enough, to be able to move on to the next step:
I used the Difference of Gaussians tool. In GIMP this is in Filters>Edge-detect>Difference of Gaussians to create the outline below, which I scaled to fit my 12" x 12" work. It didn't matter that the edges weren't even, I smoothed those out when I cut out the template.