The web page below measures reflected light. However, the basic idea is the same as measuring fluorescence in microscope image. Click here for a primer on measuring fluorescence in micrographs.
Looking at two chairs, I noticed that they appeared to be very different intensities. The one on the left looked much brighter than the one on the right. I figured that a photo wouldn't capture this, but it does an okay job, although looking at the chairs in situ, the difference is far more dramatic. In real life, the chair against the wall looks far brighter than the one in front of the window.
Measurements of the intensities of each chair back shows that they are, in fact very similar, essentially the same. Measurements 1 and 2, in a scale from 0 to 65535, are very close and the chair against the window may even be brighter.
Other intensity measurements are shown in case you want an idea of the range throughout the image.
The main point of this exercise is that human visual perception of intensities is highly variant based on local contrast conditions but a good camera or other detector is uniform across the field and as conditions change with time. Want to measure intensities? Use a computer.
Yes, the camera had uniform response of pixels across the field (although don't know if gain is strictly linear and, as shown by screen snaps, gamma not linear-- not essential for this problem). The photo was taken with a Sony RX100II camera and the raw mode image was converted to 16 bits with all sharpening and noise reduction settings off and contrast linear. The color image was converted to grayscale by a median projection of the three colors using ImageJ 1.52. The picture shown below was rescaled using bilinear interpolation and all measurements were done on the original median projected image.
Try this.
1. Rank the average intensities of the four squares below from brightest to darkest.
2. Are all the squares uniform intensity? Another way of asking this is, are they flat or do different parts of the squares have different brightnesses? If any squares vary in intensity, which ones are they?
