Saturday Jan 29, 2011

PnmBlend Disappearing Act

Recently I was working on an automated tool to create images of 19" racks with their content. I got a nice picture of the new Cisco R42610 rack, but with the doors off, it still showed the hinges. No big deal, but it made the picture a little ugly.

I wanted to let those hinges disappear and had to be able to make it a repeatable thing. Therefore I didn't want to do it with PhotoShop, but preferred to script it using NetPbm. Now, NetPbm didn't have the right tool for the job, so it was time to write my own. Wasn't the first time, ten years ago I wrote together with Alex the pnmtopng/pngtopnm converters and more recently I contributed "pnmmercator", a cartography application.

The result of my current effort is "pnmblend", a little utility that will take the top and bottom row of an image (or the left and right column) and replace everything in between with a fading (or gradient) from one to the other.

hinge 1   hinge 2   hinge 3   hinge 4   hinge 5

On the left you see the rack with the hinges still there. The next picture zooms in and the third shows the piece we've cut out to work on with "pnmblend". After that you see the output of my new utility and the last image is the result of putting it back in the original image using "pnmpaste".

This code isn't yet ready to be included in the official NetPbm package. For that I've to convert it from a 'pnm' to a 'pam' utility. Secondly, the current code isn't based on the NetPbm libraries, but is doing it all in itself. Which could in certain cases even be an advantage.

Update March 2011: This code was included in NetPbm under the name pamwipeout