The Cone - A colour question

[Bolts_Tweed (Mark)]

Gday

Forget this image it is just to show what I am discussing (it is just a RGB waiting for Lum). I have been musing about colour of images of faint dust lately and i'm in a quandry. I get this result with standard RGB setting and I am now taking Ha channels to form a Ls with Ha+R and I have found myself wringing the neck of images with Ha channels to make them red (see http://www.leyburnastronomy.net.au/mbfox.htm for what I mean) and for the life of me I am having trouble understanding why I do it. It must be because they have a Ha component and my brain says they must therefore be red (i.e. HII region) but I am not sure that is the case.

I recently imaged the full moon in HaR, HaR,G,B to improve contrast and I dont force it to red. I decided to check my bible and guru on colour (David Malin) because he is the only person I know that used greyscales on his plates to try for true colour and some of his images show this region in a brown lighter than mine and some show it in birght HII red. So I am lost. Also see Gendlers image of this area.

If I have a strong Ha (red) component and an equally strong G & B component it is going to be white - the presence of a Ha component doesnt immediately make an object red but if the Ha is strongly dominant over the G & B it will be a shade of red. This image is from exposures adjusted for filter effects so i'm lost.

So I am starting to think this slightly reddish brown colour might be closer than the strong red I usually see this area imaged in (myself included so this isnt a criticism in any form) with the subtle red of the HII region near the newer stars that cause the refletion nebulosity.

Just the musings of old fool with too much time and too many clouds to do anything else.

Mark

[jase (Jason)]

Mark,

Colour is subjective and by no means of the imagination am I going to attempt to bring resolve to such a matter. In many cases it comes down to what and how the imager wishes to portray in an image. I know others will have thoughts on this topic.

There are minimal rules with narrowband imaging so will not cover these here, but getting a HaRGB blend right takes some work. Firstly, ensure you've got an accurate G2V weight ratio for your gear. If you don't, you're wasting your time to begin with.

Secondly, produce a straight RGB combine image using these G2V weightings. Gradients and other anomalies aside, a straight RGB is as close and as pure you'll get in terms of accurate colour. As soon as you add a luminance or Ha layer, the colours shift. Take a good long look at the colours of the straight RGB as this is ultimately what you want to replicate once you've added a Ha or luminance blend to it. The point of adding Ha data to the red channel is to simply colour the Ha data in luminosity layer. Nothing more, nothing less. How much you need to blend depends on how intense the Ha data is.

While it is ever so tempting to operate at 100% opacity with the Ha luminance for maximum detail, you'll find it hard balance/restore the colours back to what you saw with the straight RGB image. Try dropping the opacity percentage of the Ha luminance, flattening, boosting the saturation, then relayering the Ha luminance again at a higher percentage. There are a few other tricks to handling this.

The point here is what ever you see in your original straight RGB image should be your goal to portray in the final composite. Stretch it via DDP to get a feel for the dusty areas as opposed to the stronger Ha emission elements in the image. Anyway, this is the methodical process I utilise. I'm sure others will share their own.

Cheers

[Bolts_Tweed (Mark)]

Thx for the reply Jase

Yeah colour I agree is a taste thing. Some like Bach some like Led Zepplin but its all music and who's right. NB i agree too - I mean I love some of Tom Davis' and Eddie T's nb stuff - different palettes but both great.- but I am really thinking that the presence of a Ha channel doesnt instantly make an object red for me anymore. I can see the house light through the 6nm filter and thats a perfect example of what I am trying to explain.

I have G2 calibrated the filters and thats what put this notion in my head. . I tihnk I am going to follow my nose with this colour thing.

Thx for the Ha Lum tip - I haven't tried changing the opacity before - I usually try and replicate RGB colour after pasting in the Lum but this sounds like a good idea. Will see how I go with full Lum data this moon.

Mark

[AlexN]

Another thing that really helps with keeping the colour balance looking nice is to blend the Ha with the red channel 70:30 and using that as R, instead of using Ha as a L channel.

The 3rd option is to layer the Ha in as a L layer, then copy the colour layer, paste it into the image again, and make that layer reside between the Ha and the colour data, set its blend mode to multiply and adjust the opacity to taste. at 100% it will make the image pretty ugly usually.. I find anywhere between 30% and 70% does the trick depending on the image...

Ps - Your Cone image is looking really nice.. If I recall correctly it was a little garish when you first posted it!