Now you've got me thinking. I could be way outside the box here
Quote:
|
I thought that the histogram was a representation of the range of brightness levels (0-255) across the bottom axis (X-axis) and a representation of how many pixels of intensity “n” fell into each brightness level (Y-axis).
|
That's about how I understand it as well, the histogram is a measure of the range if brightness levels across the x axis and the y is the number of electrons at each level.
But a large hump in the middle, as I understand it, represents lots of pixels that have their well half full, ie they haven't reached saturation yet. The closer to saturation the further to the right a particular well will appear. So if the aim is to have the chip exposed for a flat so that it reaches between 1/3 and 1/2 full well capacity then a good sharp spike between those ranges would tend to indicate that. The Histogram is giving you a graphical representation of the numeric distribution of the images electrons based on intensity, not physical pixel site.
An example of this would be the more spread out the hump more your vignetting. You can see by the image that there is vignetting around the edge, ie less electrons per pixel. This is shown in the histogram by the tail to the left.
Maybe I'm way out, but it seems to work.
