Processing colour in unbalanced exposures

[Lawrence]

I'm puzzled about a quotation in the colour processing module:

"StarTools enables you to keep M42's colour constant throughout, even in its bright core. No fiddling with different exposure times, masked stretching or saturation curves needed. "

In M42 the trapezium stars are bleachd out in any normal exposure length so to maintain them as 'real' one has to take a separate exposure. The above suggestion implies that one exposure fits all. I am still a beginner with ST so I would appreciate a further explanation if possible?

TIA

Lawrence Harris

[admin]

Hi Lawrence,

StarTools will attempt to recover color in pixels that have not been overexposed in any of the channels. The "bleaching out" so often seen is an artefact of processing techniques; it is not inherent to the data. Stretching the data as a whole will cause colors to be stretched/compressed as well. This causes desaturation in the highlights and distortions elsewhere. By separating luminance and color and only stretching luminance, this distortion of coloring can be avoided.

Making a high dynamic range composite is never done to recover coloring, rather it is done to recover detail. Depending on how deep you'd like to go, a single exposure of M42 may indeed be enough.

I hope this makes sense,

[Lawrence]

Hi Lawrence,

StarTools will attempt to recover color in pixels that have not been overexposed in any of the channels. The "bleaching out" so often seen is an artefact of processing techniques; it is not inherent to the data. Stretching the data as a whole will cause colors to be stretched/compressed as well. This causes desaturation in the highlights and distortions elsewhere. By separating luminance and color and only stretching luminance, this distortion of coloring can be avoided.

Making a high dynamic range composite is never done to recover coloring, rather it is done to recover detail. Depending on how deep you'd like to go, a single exposure of M42 may indeed be enough.

I hope this makes sense,

Yes, it does. Thanks. I'll look back at my data.

Lawrence