Enfuse is a command-line program used to merge different exposures of the same scene to produce an image that looks very much like a tonemapped image (without the halos) but requires no creation of an HDR image. Therefore it is much simpler to use and allows the creation of very large multiple exposure panoramas. … Read more
March 5, 2008
January 21, 2008
“sketch” images
A tutorial on using the GIMP to create “sketch” images. Great for creating coloring pages for kids, as one person pointed out.
Here’s a Photoshop version of the above, sent by my brother, David.
December 22, 2007
Lens correction with Fulla
I’d like to draw your attention to a little command-line tool that I’ve run across that is very good at doing one thing: lens correction. It uses the panorama tools library (yes, the same excellent one by Helmut Dersch, now a full open source project) to do lens corrections based on (my research is weak here) mathematical models for optimal lens behavior. I installed it on Ubuntu easily by:
$ sudo apt-get install hugin-tools
The man page describes it thusly:
“Apply radial or flatfield vignetting correction as well as geometrical radial distortion and transversal chromatic abberration correction.” (sic)
I mostly use it to correct for the barrel distortion and vignetting that occurs using my zoom lens at the widest setting. It sounds like it can correct for some types of chromatic aberration as well. The extra cool feature of this tool is that it can read the camera make and model from the EXIF data and look up the necessary coefficients in a database (just some flat text files) stored in your home directory. It’s a little tricky to get the database set up and to figure out the correct string to use, but from then on out it’s dead simple to use. Here’s an example:
$ fulla -p -a -m 'CASIO COMPUTER CO.,LTD' -l Standard -o R20070202-172308-cor.png R20070202-172308.jpg
Casio EX-P600, Lens Standard @ 7.100000 mm
PTLens coeff: a=0.020742 b=-0.051562 c=0.000000 d=1.030820
correcting image: : |
Before and after. Click on the pictures to view them in Flickr and then select “All Sizes” to see the effect of the barrel distortion and correction better at larger sizes. I’ll post another example later that shows the vignetting correction.
The only other limitation is that the camera database does not seem to have been updated in a while. For example, I found my main camera, the Casio EX-P600 in there, but not my newer Fujifilm F31. The author of the database, which was for a separate project (ptlens), took that project closed-source and encrypted the database at some point. If anyone knows of a source for an up to date database with newer cameras i’d love to hear about it.
