PhotoPerfect Manual

Measure Hot Pixel Reference

Where long exposure times are involved (over 2 seconds), a large number of bright points appear (so-called hot pixels, which are caused by the way the camera sensor functions). The effect is like a starry sky, but not necessarily what you want. To solve this problem, another shot is taken immediately before or after the true picture, but with the lens fully obscured (e.g. with lens cap. This image contains only the hot pixels, which can then be subtracted from the proper image.

To this end, first set the hot pixel reference:

Measure hot pixel reference
The (black) reference image must be loaded. The histogram displayed shows the number of image points per brightness value (black to white = left to right). The display can be scaled using the left, vertical slider. The great majority of the points will be on the left side (black). Now it is a question of setting the lower, horizontal slider (which moves the red mark) to a threshold from which no longer black, but hot pixels are recognized.

Correct hot pixels
For this, the reference must already be set and the image to be corrected must be loaded. If the threshold value was set too far to the right, then not all the hot pixels will disappear. If it was set too far to the right, then all the hot pixels will disappear, but  also the image will become altogether less sharp.