FITS images binned

[bomberbaz]

Simple question really.  I was under the impression that binning OSC camera's gave you results in mono, is this not the case 🤔

[vlaiv]

20 minutes ago, bomberbaz said:

Simple question really.  I was under the impression that binning OSC camera's gave you results in mono, is this not the case 🤔

Depends on how you bin them.

Binning is trading spatial information for improvement in SNR. You basically "stack" adjacent pixels, so it is form of stackin but instead of temporal "direction", like stacking multiple exposures, you use spatial direction - you sum adjacent pixels.

With OSC data you have two choices - you can pay attention which adjacent pixels you stack and preserve color, or you can just stack closest ones and then you destroy bayer matrix information and loose color.

If you take 2x2 groups of pixels and produce single pixel in output - you loose color information.

If you take 4x4 groups of pixels and produce 2x2 group of pixels in output with paying attention to only add relevant colored pixels together - you preserve information (and get the same result as if you used OSC camera with twice as large pixels but half of the pixel count in horizontal and vertical).

[bomberbaz]

2 hours ago, vlaiv said:

Depends on how you bin them.

Binning is trading spatial information for improvement in SNR. You basically "stack" adjacent pixels, so it is form of stackin but instead of temporal "direction", like stacking multiple exposures, you use spatial direction - you sum adjacent pixels.

With OSC data you have two choices - you can pay attention which adjacent pixels you stack and preserve color, or you can just stack closest ones and then you destroy bayer matrix information and loose color.

If you take 2x2 groups of pixels and produce single pixel in output - you loose color information.

If you take 4x4 groups of pixels and produce 2x2 group of pixels in output with paying attention to only add relevant colored pixels together - you preserve information (and get the same result as if you used OSC camera with twice as large pixels but half of the pixel count in horizontal and vertical).

Hmm this is what I did, 2x bin but still have a colour image. I have confirmed the binning in ASTAP but have a colour image. Seems something is not quite right.

[vlaiv]

56 minutes ago, bomberbaz said:

Hmm this is what I did, 2x bin but still have a colour image. I have confirmed the binning in ASTAP but have a colour image. Seems something is not quite right.

Everything is right if done properly.

Bin x2 simply means following:

- reduce width and height of the image by x2

- improve SNR by factor of x2

- average 2x2 pixels to produce single output pixel

(see there is everywhere number x2 present - similar thing happens with x3 bin and x4 bin and so on, except different number appears in each statement).

In order to get black and white image - following must happen:

You take group of 2x2 pixels of different "color" (different filter of bayer matrix) - and you average those to form output pixels.

But if you do following:

you take only red pixels (2x2 of them) and average them to red pixel, and you take 2x2 neighboring blue pixels and average those to one output blue pixel and you do the same with "top left" green group and "bottom right" green group - you preserve color information because you only average red with red, green with green and blue with blue pixels.

Only when you average red, green and blue pixels together do you loose color information (in top example).

 

[bomberbaz]

1 hour ago, vlaiv said:

Everything is right if done properly.

Bin x2 simply means following:

- reduce width and height of the image by x2

- improve SNR by factor of x2

- average 2x2 pixels to produce single output pixel

(see there is everywhere number x2 present - similar thing happens with x3 bin and x4 bin and so on, except different number appears in each statement).

In order to get black and white image - following must happen:

You take group of 2x2 pixels of different "color" (different filter of bayer matrix) - and you average those to form output pixels.

But if you do following:

you take only red pixels (2x2 of them) and average them to red pixel, and you take 2x2 neighboring blue pixels and average those to one output blue pixel and you do the same with "top left" green group and "bottom right" green group - you preserve color information because you only average red with red, green with green and blue with blue pixels.

Only when you average red, green and blue pixels together do you loose color information (in top example).

 

What I did vlaiv was 2x bin in ASI Air whilst taking the subs, this is why I cannot understand as they should be B&W given that 2x bin can only be given you only have the one red, one blue and two green, or am I missing something very simple. 

[vlaiv]

3 minutes ago, bomberbaz said:

What I did vlaiv was 2x bin in ASI Air whilst taking the subs, this is why I cannot understand as they should be B&W given that 2x bin can only be given you only have the one red, one blue and two green, or am I missing something very simple. 

And do you know what ASI Air did when binning the data? Did it perform operation that I outlined above? If so - color can be preserved.

Do have another look at my previous post - it explains two different ways of x2 binning that can be performed on OSC data. Both are bin x2 - and one is "naive" bin x2 - that is suited to mono data and destroys color information - while other is still bin x2 - but it is suited to OSC data and preserves color.

If you have color data in the end - second version was performed.

[bomberbaz]

2 hours ago, vlaiv said:

And do you know what ASI Air did when binning the data? Did it perform operation that I outlined above? If so - color can be preserved.

Do have another look at my previous post - it explains two different ways of x2 binning that can be performed on OSC data. Both are bin x2 - and one is "naive" bin x2 - that is suited to mono data and destroys color information - while other is still bin x2 - but it is suited to OSC data and preserves color.

If you have color data in the end - second version was performed.

I am not aware there is more than one bin option in ASI AIr, I shall have a look later

[vlaiv]

27 minutes ago, bomberbaz said:

I am not aware there is more than one bin option in ASI AIr, I shall have a look later

There probably is not, but ASI Air is aware that you are using OSC camera and can choose bin method based on that.

Only thing that you can do is select - bin x2, and it will apply appropriate bin method based on whether it detected an OSC camera or not.

[bomberbaz]

On 23/04/2023 at 18:59, vlaiv said:

There probably is not, but ASI Air is aware that you are using OSC camera and can choose bin method based on that.

Only thing that you can do is select - bin x2, and it will apply appropriate bin method based on whether it detected an OSC camera or not.

Thanks for your help in this thread vlaiv. I have been over this and other matters since but I think I am now getting a better understanding of how these things work. Sometimes they seem counter intuitive but when you thinnnk it through, it makes sense.