Saturday, January 5, 2013

Recreating a Stamp - Color to Alpha in GIMP

I want to go through a process of how I got...
from here...
to there.
It all started when I read an article of how to create a watermark in GIMP. For that, I used the text editor and created variations of @xindilini. I hadn't even figured out how to save the resultant paintbrush at the time. Then I remembered my chop. It is a customized stamp with my Chinese name carved in stone. The one I had in mind was the one that would produce a negative image of the characters.

I took a picture of the imprint with a webcam and started playing with the image in GIMP. After loading the image file, I created a new layer of the specific area so I could rotate it arbitrarily. Autocrop Layer. Autocrop Image.

Tried a few options from the Colors > Auto and settled for Stretch HSV. This would stretch the image contrast to cover the maximum possible range.
Now we are ready to use Color to Alpha. You can select this from the Layer > Transparency menu or directly from the Colors menu. Both will do the same thing. Other than the red inky parts are transparent because the default colour is white. If you want to change it you can click on the rectangle as shown in the following image.
I put it through one more pass to get the red to pop out some more. That is the by using Maximum RGB from the Colors menu. This will reduce the image to pure red, green, and blue. For this purpose, make sure the option "Hold the maximal channels" is selected.
You can now save the layer for later use. I took it one step further by combining it with calligraphy of my name. Since I am a bit out of practice, I traced it out by hand. Converting the image mode from RGB to Greyscale, I could use it for a watermark on dark or light images alike.
I really liked playing around with Color to Alpha. Can't wait to try it with other stamps or cutouts.

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