Can you take luminance with a OSC camera?

[swag72]

I read that Luminance is most important when using a mono camera, while the RGB stuff is just to overlay some colour into the luminance channel.

Can you then get luminance using a filter and a OSC camera? Maybe it is the same principle as Ha, where you are only really capturing 1/4 of the data due to the bayer matrix? But you can capture it nonetheless.

Just one of my off the wall thoughts!!

Edited May 4, 2011 by swag72

[martin_h]

Not realy....An OSC creates a false luminance within its self but you cant get at it..Binning at say 2x2 will give you mono but at lower resolution, so not worth it, because you need the highest resolution for the Lum.

[swag72]

What would you get if you put a luminance filter over the front of a OSC?

[MartinB]

Hi Sara, yes you can create a luminence with a OSC camera and it can but useful sometimes as well. All you need to do is convert your colour image to greyscale. You then treat your greyscale as your luminence and your colour as a combined RGB.

[Zakalwe]

What would you get if you put a luminance filter over the front of a OSC?

You could do that, but then only 1 in every 4 pixels are recording data (because of the Bayer matrix) which lowers the resolution

Having said that, at some point I am going to experiement with this. My CCD has a 6 megapixel APS sensor, so I still will have 1.4 megapixels recording data, albeit over a large area.

[MartinB]

Just to clarify, there is no such thing as a luminence filter! A colour image is made up of 3 components - hue, saturation and luminence. We have no trouble understanding hue and saturation. The luminence is the component of a picture which provides all the detail. It doesn't have a hue or any saturation, in other words it is a greyscale image. Normally, when doing LRGB image a filter is used, this can be a plain filter to make the luminence par focal with the RGB filters, it could be an infra red blocking filter or a light pollution filter. But you could also collect luminence data without using any filter at all.

For OSC you use your data both to provide RGB and L components. There's no need to do a seperate run to collect luminence. The different treatment comes in the processing. Apart from converting to greyscale you will apply some sharpening and probably some contrast tweaks to the luminence to enhance detail. With the colour you wouldn't apply any sharpening, in fact you could even apply a small noise reducing blur (but not to the stars!).

[ollypenrice]

Yes, there is some confusion here. An OSC camera with the usual UV/IR blocker is producing the best 'luminance' of which it is capable. I think Zakalwe is mistaken, here. If you put a Luminance filter in front of an OSC camera you will get what you would get without it, an OSC image with an interpolated luminance layer.

Various programmes will extract 'luminance' from an OSC image. For instance, in Ps you can go into LAB colour mode and one channel is the Lightness. This is worth processing differently as Martin says. It is like processing a luminance layer. You push for detail, contrast, sharpness (another word for contrast really?). In the other channels (colour) you are interested in saturation and noise reduction but not detail. One mono advantage is that you can collect this layer faster by letting all of the pixels collect all of the colours simultaneously.

I may be wrong on some of this because I am not a technical bod as an imager but I think in essence a luminance filter is just a UV/IR blocker, no?

Olly

[martin_h]

I may be wrong on some of this because I am not a technical bod as an imager but I think in essence a luminance filter is just a UV/IR blocker, no?

Olly

Yes it is.

[Zakalwe]

Yes, there is some confusion here. An OSC camera with the usual UV/IR blocker is producing the best 'luminance' of which it is capable. I think Zakalwe is mistaken, here. If you put a Luminance filter in front of an OSC camera you will get what you would get without it, an OSC image with an interpolated luminance layer.

Thanks Olly...you are, of course, correct. I was getting confused* with narrowband filters.

*It happens regularly.

[swag72]

Ahh, OK. As you know I do like to think about what is possible with OSC camera's and have asked a couple of similar and probably rather naive questions as I try to understand how I can improve my DSLR images, as I want them to be the best I can possibly get.

I too was probably confused with NB imaging, thinking that luminance was somehow similar to Ha capture. I didn't realise how intrinsic it is to the whole colour image as a whole when taken with OSC. I though that maybe it could be seperated out somehow to improve OSC images.

Well, it's back to the brain farts for me then!! Until I have another .............. Adios!!!!

[steppenwolf]

I though that maybe it could be seperated out somehow to improve OSC images.

Hold on, Sarah, don't go just yet!

As Olly has suggested, you can extract a 'form' of luminance channel and process it differently to the OSC data and then combine the data to produce a quasi-LRGB image so, give it a try.

Olly's method is good but if you don't have PhotoShop then you could just copy your image, convert it to greyscale and process it for detail just like the Lab suggestion. This is commonly done for producing colour saturated Moon images but it can also be used to good effect on DSOs.

[swag72]

Worth a try then sometime I reckon. How does making an image greyscale improve the overall image when you have layered it back in? I presume that you would use layers to get the 'luminance' back into the image? And just overlay it at an acceptable percentage?

[shaunster]

Overlay it and set blend mode to luminence in photoshop

Edited May 5, 2011 by shaunster

[MartinB]

How does making an image greyscale improve the overall image when you have layered it back in? I presume that you would use layers to get the 'luminance' back into the image? And just overlay it at an acceptable percentage?

Add back in as Shaunster says. You do things to a luminence layer that you don't want to do to your colour layer. The colour layer is purely for hue and saturation, not detail. It doesn't need sharpening, this will add chrominence noise which is best avoided. In the colour layer you concentrate on tweaks to hue and saturation.

[Vallantho]

In photoshop and maybe affinity, haven’t checked, you can switch to the L a b colourspace which gives you a luminance channel separated from the a and b channels which contain the colour information. So you could open a new copy of the document in L a b mode, make edits to the luminance channel, which is basically just adjusting contrast, noise reduction also works well on the luminance channel, then copy that into a layer on your original image and pick your blend mode to taste 

[Vallantho]

Just now, Vallantho said:

In photoshop and maybe affinity, haven’t checked, you can switch to the L a b colourspace which gives you a luminance channel separated from the a and b channels which contain the colour information. So you could open a new copy of the document in L a b mode, make edits to the luminance channel, which is basically just adjusting contrast, noise reduction also works well on the luminance channel, then copy that into a layer on your original image and pick your blend mode to taste 

Just realised this was a thread from 2011. Duh 

[Mexximus]

Dont worry Vallantho you have helped me 12 years later 😂