What makes a good Luminance image?

[MattJenko]

Title says it all really. What are the attributes that you go for in processing Lum images and why?

[MattJenko]

I'll start and people can correct my inevitable simplifications and starting conclusions.

To my mind, luminance is as described by Robert Gendler: http://www.robgendlerastropics.com/LRGB.html and is an attempt to give back a level of detail that can get lost when combining individual colour channels and is as a result of how human perception works as we are very sensitive to changes in brightness as opposed to changes in hue and saturation. This means Luminance data should be high contrast and a Lum image should be the sharpest it can be and have a good range of brightnesses to accentuate the features you are interested in highlighting in the image, in proportion to the data gathered.

This to me means that a Lum image needs to be sharp, noiseless and should therefore be carefully processed across the board, as opposed to some of the RGB channels and additional data subs, like Ha when blended into the red channel. From some serious imagers on here, I have also found out that Lum is not really required for stars, and star-fields should be RGB only where possible, as a brightness layer is not required and can actually be counterproductive, in which case, stars in a Lum image should be as small as possible, if included at all.

Cheers

Matt

[andrewluck]

There's been some interesting discussions on this subject on the Pixinsight forums. Search for LRGB vs RGB. Juan's position is stated pretty clearly here:

http://pixinsight.com/forum/index.php?topic=1636.msg9297#msg9297

An interesting post.

Andrew