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Alex Pratt

登録日: 2012.01.17
記事: 29

記事日時: Wed Sep 23, 2015 12:38 am    記事の件名: Contrast 引用付きで返信

Hi SonotaCo,

The Night Sky Observation Guide recommends setting gamma OFF (=1.0) to obtain good contrast of the night sky.

Our team's cameras are set to gamma off (1.0). Some stations use PCI capture cards, others use USB capture devices. Both of these types of capture devices have brightness and contrast controls.

I use high contrast settings on my PCI card (camera) and USB device (camera 2). Some of my colleagues prefer to use low contrast settings. I like rather high contrast, otherwise the video clips and still images are flat grey, with little contrast.

What is your recommendation?

Clear skies,

Site Admin

登録日: 2004.08.07
記事: 9791
所在地: 139.67E 35.65N

記事日時: Wed Sep 23, 2015 7:15 am    記事の件名: Re: Contrast 引用付きで返信

It is difficult to say generally.
Sensitivity and the S/N is surely important but brightness and contrast is not so important. The optimal setting will depend on the purpose, sysem and the condition of the night sky.

Yet, in general, I am thinking any additional modification to the video signal will cause loss of information.
They can improve the looking of the video for human eyes, but may decrease the automated detection ability.
So I am not recommending the use of gamma or other level controls.
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Alex Pratt

登録日: 2012.01.17
記事: 29

記事日時: Fri Sep 25, 2015 10:30 pm    記事の件名: Contrast 引用付きで返信

Hi SonotaCo,

Thanks for your comments.

I did a quick check and the S/N from low-contrast and high-contrast cameras were very similar.

I will investigate this further.

Clear skies,


登録日: 2007.10.19
記事: 154

記事日時: Thu Oct 08, 2015 2:32 am    記事の件名: 引用付きで返信

If you use a Watec or similar camera connected via a capture device, the settings on the camera should be adjusted to the local conditions. If the light pollution is bad, gamma = 1.0 is fine. Else it is better to increase. The gain should not be too high, it only enhances noise visibility and loss of highlights. The capture device settings should not be too contrasty, respecting the range of values of the camera. The SNR is fixed, you may see changes in noise level, but signal scales similarly.
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