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Post by Deleted on Mar 18, 2014 19:28:22 GMT
Ok heres a topic for discussion....
Up until very recently this is something i didn't know about. Didnt have a clue. Didnt care to be honest. Im guessing anyone who has done any astrophotography will instantly know what it is and how it works. But for me it was just something i didnt go near. Hemmi walked me through it on NSN but i still didnt know what i was doing. I only ever play with the normal settings brightness, contrast, sharpness etc...
All i know so far is to move the left hand slider to the start of the peak in the graph to make the background darker.
Whats peoples thoughts on this? Got any tips on how best to use the histogram settings? Ive read playing about with it on certain objects brings out more detail etc...
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Post by Deleted on Mar 18, 2014 20:49:18 GMT
Chris,
You have the gist of it. I will give you some tips that I have learned over the years. I too am no expert but I can give you my experience.
First you want to look at the largest peak. If this peak is center to right, your gamma is to high. Lowering gamma should shift the peak left. Once the peak is left of center, then you can clip out the sky glow. You do this by moving the left slider to the being of the peak.
There is no perfect position, you just play with it till you get the best image.
Now this just reference Luminosity histogram, you can also adjust the histogram per color. Lets say your on a target such as M51 with lots of blue, but your image just appears dull and gray. You can try just clipping the red and green, and even increase the blue by sliding the right slider of the blue histogram left some.
Normally you would only adjust the luminosity histogram, but each color has its own histogram, so you could adjust each separately for the best image.
Playing with it is all I can tell you.
I'm sure someone on here with much more post processing knowledge can give you a better answer. All I know is what I have tried. But to me the histogram is the best tool in miloslick. It has the potential to really enhance the details in your image.
Now its time for someone who has a clue to chime in LOL
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Post by Dragon Man on Mar 19, 2014 6:21:51 GMT
Here's a nice simple way to understand a Histogram and where it needs to be with our cameras for Astronomy use. I have made a diagram using a real Histogram: ORANGE - shows where you preferably want the peak of the histogram. One third along the way along the graph is best with a small amount of zero reading at each end. BLUE - shows the areas affected in an image. The Dark areas (the dark sky), the Mid-tones (like faint galaxies and nebula), and the bright areas (like stars and bright nebula). GREEN - The sliders in Processing software. In Miloslick it is the controlled by changing brightness and contrast in the Video Settings tab. RED - The limit you should only go to. If you use the sliders or Brightness/Contrast and move these boundaries too far you do what is called 'Clipping'. You clip off too much data. The worst one is Black Clipping. It makes an image (or view) look too dark and lifeless. The best way to have a Histogram is to have the peak at 1/3rd along the graph, with the clip point before the start of the black peak, not on it. You can clip the brightness end slightly more to reduce skyglow, light pollution, over-exposure etc. Here is Miloslick showing the Histogram in the best position, and how to control it using the Video Settings sliders:
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Post by Deleted on Mar 19, 2014 10:33:08 GMT
Excellent info guys! Thanks for this. Im sure it will come in handy!
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Post by Deleted on Mar 19, 2014 11:09:16 GMT
Question...as i didnt know brightness and contrast changed the histogram... to date i pretty much always have contrast at 100% on everything i look at. Is that wrong?
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Post by Dragon Man on Mar 19, 2014 13:14:43 GMT
No Chris. I also like Contrast at 100% on most objects. But have a look at the Histogram and see how it sits. If the level on the right hand end is too high, just nudge the Contrast down a bit and have another look at the histogram. What you don't want is the level too high on the right hand end. But if your live view looks better with 100%, use it. I do Often I will drop it back on M42 to lower the core a bit. You can get away with the right hand end (the bright data) clipped a bit. Just don't clip the left hand end (the dark data).
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Post by Deleted on Mar 19, 2014 15:59:39 GMT
No Chris. I also like Contrast at 100% on most objects. But have a look at the Histogram and see how it sits. If the level on the right hand end is too high, just nudge the Contrast down a bit and have another look at the histogram.What you don't want is the level too high on the right hand end. But if your live view looks better with 100%, use it. I do Often I will drop it back on M42 to lower the core a bit. You can get away with the right hand end (the bright data) clipped a bit. Just don't clip the left hand end (the dark data). Lowering Gamma helps with this too. But if gamma is already at its lowest, yes lowering contrast helps move the peak left.
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Post by Deleted on Mar 20, 2014 12:05:33 GMT
Good stuff, Guys! Will have to play more. Had become "disproportionately scared" of (theoretical) ideas of over-doing the contrast? Also that (Watec) hardware Gamma "introduced noise". Maybe so, but I am now reverting more to my original ideas: Watec Hardware Gamma "Lo" (0.45), Gain ~50%; Software Brightness 50%... BUT now (once more) allowing software Contrast > 50%! Simply, my histograms were just way too narrow. Modest stretching resulted in a comb-like structure, reflecting the digitising - Ultimately FOUR (Not Fifty!) "Shades of Grey"? lol With only 8-bits to start with, once the data has gone, it's gone. Just taking more note of the *histogram*, on individual basis, rather than (supposed) "best" settings.
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Post by Dragon Man on Mar 20, 2014 15:28:14 GMT
Here is a great link to explain why a Histogram does what it does, how to get a good Histogram, and the explanations of weird effects like Chris Macavity's comb-like structure. www.astropix.com/PFA/SAMPLE3/SAMPLE3.HTM
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