Monthly Archives: August 2006

Just fix it

A couple days ago I found the most egregious error I’ve ever seen on wikipedia, not a graffiti issue, something that was wrong and had been wrong for a long time — since September 15 2004, on the DNA article. A picture of the chemical structure of DNA. It was in fact a “featured pictures” candidate for September 2004; it’s a little funny that all the comments about it failed to see the structure was wrong (a little sad, too).

Below is my marked-up version that points out all the errors (click it to get more resolution).

What I noticed, the immediate problem, was the base-pairing. In this picture the oxygens of guanine and cytosine were paired with each other, instead of with NH2. It looks like the author simply rotated a DNA strand 180 degrees and lined them up, not noticing that this actually fails to orient the bases appropriately. Maybe the problem is inherent in flattening a three-dimensional structure. Maybe it’s because the ribose connections of paired nucleotides are not opposite to each other, and this causes a “minor” and “major” groove in the backbones.

Anyway, I used ChemTool and GIMP to make a new picture and replaced all instances of the wrong-structure diagram with my new picture (in the articles DNA, Francis Crick, and GC content).

It took a long time, but I disapprove of people who complain about wikipedia errors without correcting them.

HDR Photos

On Thursday I was browsing the NY Times website while working ridiculously late, and I read this article online about “high dynamic range” photography. The problem: cameras saturate with too much light, failing to capture the full range in a scene. IE, with a short exposure the sky might be visible, but the foreground is so dark that it becomes a silhouette. On the other hand, with a longer exposure, you can see the foreground but the sky becomes a saturated white. By combining a series of photos taken at different exposures, and then remapping the values, you can create pictures which capture the land and sky. It’s beautiful stuff, you can see more in this Flickr HDR Photography group.

After reading this tutorial, I learned how to do a quick-and-dirty blending in GIMP to create reasonable “HDR” photos with a couple of layers and a mask. You define the saturated areas in the “overexposed” photo as the mask that instead exposes parts of the “underexposed” photo, thereby combining the two. I went outside (we live next to a picturesque pond) with my tripod and took a couple photos — unfortunately, my camera (a Canon PowerShot A95) doesn’t have automatic-exposure bracketing (“AE-bracketing”), so I had to adjust the exposures by hand. This means things moved around a bit in the photo, as a breeze was blowing.

The end result was still stunning.

Here is a medium exposure photo I took. The sky is saturated with white, and some of the foliage is lost in shadows.
Here the photo is very overexposed. You can see the foliage better, but the sky is completely white.
And in this one it’s very underexposed. The sky is vivid blue, but the rest is black.

Finally, here’s what I got using the quick and dirty manual masking method, combining the over-exposed and under-exposed photographs:

I love this, it’s beautiful. The next camera I buy will have to have AE-bracketing.