Quote:
Originally Posted by Paul Haese
Thanks Jase,
No reducer but I have a flattener. Can you tell me how to bring out the saturation in those star types. Always more to learn.  |
This is a tough one Paul. You're in with a chance of NGC3579 given there are subtle blue hues present. The use of the colour range tool is not going to help however as the fuzziness range will pick too much. I think in this scenario, I'd duplicate the layer, apply curves to the blue channel to bring out the highlights. Blend the layer back as "Lighten colour". You are likely to need to mask the highlights and drop the opacity however. Once you've got a distinctive blue, the colour range tool may then be more successful and selection to bring up the saturation further. Alternatively, If you only want to fix up a few of the brighter stars you could simply go to channels, highlight the blue channel, then click on RGB eye so you see all channels (RGB), but only the blue channel is selected. Then use the sponge tool with saturation selected. Run over the stars that look blue to boost their saturation. In the process, you can also desaturate the red and green channels (also using the sponge tool), but be careful as this can be quite drastic and sometimes difficult to balance Would suggest altering (lowering) the opacity and flow of the sponge tool - keep an eye on the white point as it can turn a weird hue that results in some effort to restore. Zoom right it and avoid touching the saturated areas if possible.
NGC5128 is a different story. There isn't much in the way of blue stars to begin with. The subtle blue fold beside the dust lane is present, but not much with the stars.
I can't help but think that your long exposures has all but saturated this information. Its probably worth checking for it though...perhaps use DDP to validate this as it will manage the stellar profile very well i.e. the bell curve shaped histogram across the star compared to a table top (where you've hit saturation). This is present in the NGC5128. Even the small angular stars reach the 256 level and table top out, thus are saturated (see attached). A bell shaped curve will provide better colour saturation as the star reaches the top of the curve. Table topped stars are usually crunchy, sharp or abrupt in appearance. Not often are they totally void of colour however, but contain a small tight ring around the saturation. The idea of the bell curve is the expand the tight ring into a gradient towards the star centroid. A large bell curve will look like the star is out of focus...this should clearly be avoided.
If you've lost the colour information (unlikely), I'd still recommend going deep, but take a few 300s subs to manage the stars. This is a common technique used with astro CCD's to manage the stellar profiles. Managing stars is probably one of the more complex components of imaging. I still get it wrong, but when you pull it off, the aesthetics of the image really shine.
Apologies for the Mr. Squiggle type unhappy face in the attached.
