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Sunday, February 24, 2008

GIMP - finding edges

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.

5 comments:

JANE said...

I came acoss your blog through the TIF webring. Must have been the weekend of shadows! I don't kow about you but it was great to see the shadows... yeah , SUN, whats that??? LOL Enjoyed looking at your blog, thanks for sharing!

sharon young said...

Hi Linda
i've never used Gimp, but I know a couple of people who have and like it, it looks like a clever porgram, it certainly did a good job on the shadows. Very impressive, i'll have to have a look and see how it's done in PS.
Looking forward to seeing where you go from here with it.

Lee said...

Thank you for the short GIMP tutorial, as well as inspiration! I have it installed, but every time i open it I get woozy thinking about it. I will try a short, finite project and see if I can make it do something interesting. Or at least, get myself to something besides panic!

margaret said...

A technophobe's way of doing this is to put a sheet of paper over the screen and trace the shadows ... then photograph the tracing to get the digital image for printing. But one day I'm going to have to bite the bullet and learn how to do it properly!

Linda said...

Thanks for the comments, some of you have 'no-reply' addresses so I'm responding here. I loved the mix - from Margaret's technophobe's response, which I've used often but .... I'm working in the evening when there is no sun to Jane's comment about seeing it. I agree Jane - a bit of sun makes a huge difference.

Lee give GIMP a go - because you don't have to have too many memu's open at a time you can pick and choose what you want. Sharon I guess if you can do it in GIMP you can do it in PS with bells on!