Histogram anomoly

[turfpit]

Robin

On Saturday/Sunday (12/13 July 2025), I was out imaging a 98% waning moon. SC version used was 4.1.13332. Using an Altair 183M, 0.63x reducer, Baader 610nm red pass filter on a Celestron C8. For lunar, I usually aim for ~60% saturation on the histogram.

The log graph shows 65% and the horizontal bar 49%. I elected to use the reading from the Display Histogram which seemed to be ~60%.

Capture-Histogram-bug.JPG (65.24 KiB) Viewed 2124 times

Playing back the capture in SER Player, the graph was ~175 (fluctuating) which is ~60%.

SER_Player_histogram.JPG (9.89 KiB) Viewed 2124 times

The images captured turned out OK.

Any thoughts?

Dave

[admin]

Hi Dave,

the bars that show the histogram range at the bottom are calculated from the 0.001 centile to the 99.999th centile, meaning that about 1 pixel in 100000 will be beyond the extremes of the bars on each end. With your 183M, that works out to be about 200 pixels at each end. Remembering that your graph has a logarithmic vertical scale, it will only be a few levels near 49% that are actually contributing strongly to that count - most of the tail between the low 50s% and 65% will be just a handful of pixels at each level.

This behaviour avoids the histogram bar going to 100% far too much when there are just perhaps a handful of hot pixels in the image.

cheers,

Robin

[turfpit]

Thanks for explaining that Robin.

The 65% on the log graph and the 175 on the SER Player are consistent (65% v 68%), so I know to ignore the horizontal bar for lunar/planetary work.

Dave