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Old 04-06-2008, 12:37 PM
jase (Jason)
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Join Date: Sep 2006
Location: Melbourne, Victoria
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Clive, pleased to see you've worked out the root cause of the issue being auto RGB balance. In the processing game - anything listed as "auto" I intentionally stay well away from. The only exception this is if I've masked the background to neutralise or de-saturate it. I feel the images shown present the best M8 you've done to date. Colour is always a subjective topic of imaging. If we base the reference of a G2V star (identical our Sun) for colour balance, typically pleasing results will be obtained. They are pleasing in that they are familiar to the world around us. If our Sun was like star Procyon with a spectral type of F5IV, our images would look subtly different. Despite what people may believe, you still need to work hard for your colour data, even with OSC cameras. A good G2V star white balance is the foundation. Take note of the objects elevation while shooting and make adjustments to the blue channel to counteract atmospheric extinction. Sure, you can shoot a piece of white paper and adjust your balance. It will probably get you close. Depends on what level of technical accuracy and perfection your striving for. Long subs exposures will ensure rich data and allows you do to more with it - i.e. stretch it really hard to push colours.

The processing appears good. Round stars that aren't "crunchy". A quick look in Maxim shows most stars have an intensity shift from edge to edge - a good thing. The loss of colour on and around the hourglass neb is a little concern, but I can't comment to possible causes based on the data you've presented. Usually any form of data stretching needs to be followed up with a boost in saturation to stop loosing the information. Keep in mind that heavy use of saturation is the equivlent of a linear stretch on your data. Its not always the best way to deal with certain situations. You many need to make small and methodical stretches and saturation boosts to you reach a happy medium. Alternatively, you can use the shadow/highlights tool which will perform a non-linear stretch and manage colour saturation in one go. You'll find that using this tool, you shouldn't need to stretch too far. As you raise the black point, your colour data will get richer. Again, small and methodical steps. If you want to try something different in colour management, the use of the soft light blend can deliver great results especially with star colours. First take your combined image and perform a hard digital development (DD) stretch. Make sure the stretch is pretty hard; avoid blowing out the white points. I like what DD does do the stars. In most cases (unless you've got really bad data) DD provides a near spherical look to stars. You get a gradient from edge to edge with a white point at center. Nice. Make sure your DD doesn't sharpen in the process. Once you're happy with the stretch, make a hard saturation adjustment. I typically go around the 170% mark depending on how good the RGB data is. You don't want to introduce noise; again, long subs will allow you to handle this. Once done, the image will look rather unnatural. Open this in PS and layer it over your originally stretched image as softlight blend. You may need to alter the opacity to keep things in check. In addition keep an eye on the histogram (including RGB split). Softlight blend is a darkening function so black clipping can occur if not careful. There are a few other colour control techniques I use such as similar to the process above, but create a mask and blend it as color. Depends on the target and the drastic measures I choose to take in the quest for aesthetics. Anyway, keep at it. Process the image over and over. Take a break and come back to it with fresh eyes. Add some more data, and then try it again. While people maybe keen to release/post their images almost immediately after they’re acquired, in most cases it is evident that more time processing the data would have delivered a much superior result. I'm no expert, but I do know that it takes dedication and effort to get great results...so take your time Above all, enjoy it.

Last edited by jase; 04-06-2008 at 12:57 PM.
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