So, the following picture has been making the rounds today, and well-nigh breaking the internet.
The question is: Is this a white dress with gold stripes, terribly underexposed, or is it a blue dress with black stripes, terrible overexposed? I had opted for the former, especially after I found the white version of this dress. However, the answer, as it turns out, is neither over- nor underexposure!
The first step towards answering this is to make sure that your screen is somewhat color-calibrated. In other words, use an ICC profile, as discussed here. This will take out much of the variability.
Next, consider the features of this photo. It has what appears to be an over-exposed background, no clear reference point (e.g. a white board, a human face, etc) to which one can calibrate his/her vision. This is the crux of the illusion.
If you were to look at the histogram, you’ll find that it is somewhat overexposed, but not terribly. However, any photographer can tell you that JPEGs (or any other popular formats) are typically compressed, so that it fits on an 8-bit (x 3 channels) file. That means that once saved, pushing the image around is going to cause a lot of artifacts, not all of which can be easily understood.
I suppose this was what happened, when somehow this image was adjusted (perhaps to show the fine details of the lacey bits?). I imported the JPEG into lightroom and played with it a bit, and found that a small -0.5EV adjustment was necessary to bring in some highlight details (but not much, due to the compression). Next, white balance was adjusted to get the most natural colors (e.g. not overly yellow or purple or green). The resulting image looks like this.
Since black is never truly black, excessive yellow compensation made the lace details look brown. Again, the key to the confusion is the lack of reference objects to calibrate the image. If you shoot film or manual white balance on your camera, you will be VERY familiar with the greenish fluorescent images, the bluish shadows, and the reddish/orange indoor (tungsten) images. But our eyes almost never notice these except in the most extreme of cases. Such is the wonder of human vision!