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Messages - jubeis

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Hi everybody,

We are always striving for best color rendition in astrophotography. With the Photometric Color Calibration, we have got a new, very useful tool to select the white point. For stars, most people would consider a G2V star as white reference, there have been many papers published in the past claiming that. However, is this really true? Is the sun a white star or a yellowish star? And what is the role of our atmosphere? When we look at historic publications of the last centuries, many observers described the colors of stars. They mostly found that A and F type stars are bluish white to yellowish white, G type stars are yellow and the like. A very popular book written by the famous David Malin and co-author Paul Murdin, "Colours of the Stars" (1984) is dedicated to this and other topics related to color, and furthermore contains a lot of references.

It is well known that human perception adapts to the color of light, therefore, a sunlit piece of paper always looks white to us, independently on the daytime and cloud conditions, meaning color temperature. On the other hand, when I observe Capella (spectral classes G8/G0, binary system), it clearly shows a yellow tint to me.

So what is the correct white reference point spectral class for stars? Really G2V, or perhaps A5, or F0? It would be very interesting to hear your opinions.

Juergen

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Hi Georg,

I get the white picture from any of the NGC 1808 grey images of the project, too, if I apply Auto STF. This only happens if the link channels buttons is activated (which actually makes no sense for grey images). If channels are unlinked, Auto STF behaves as usual. Some other attendants of the EPIC 2014 experienced that, too.

Juergen

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Bug Reports / Bug in CalculateSkyLimitedExposure Script
« on: 2013 August 14 17:35:21 »
Hi all,

There is still a major bug in the CalculateSkyLimitedExposure Script of PI 1.8 RC7 (Win 7). The script itself is working, but when I close the image, every time a "Fatal Error" box appears with the message: "Access violation: invalid memory write operation at address 000000000000040E". Not a major thing because you might not use this script very often, but nevertheless annoying.

Juergen

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Dear all,

I am quite new to Pixinsight but recently I made exactly the same  ringing experience with 2x2 binned subs as Jeff. Before I found the solution with bicubic spline and 0.1 clamping, too, I tried the nearest neighbor algorithm which was war from optimum but still acceptable. I am considering, however to reprocess the whole RGB set.

Regarding 2x2 binned vs unbinned RGB subs, I also think that it can be of advantage to go for more depth in the individual subs. I accidentally took a 10 min unbinned B sub along with my L subs and compared the S/N ratio with a set of 2x2 binned 5 min B subs of the same field. The unbinned shot had an S/N of 23, whereas the binned shots showed S/N numbers of 47 each. This clearly shows that I would have to invest much more total exposure time in case of taking unbinned RGB subs. Considering the maritime climate of NW Germany, there would always be a high risk of clouding or fogging in during a session.

- Juergen

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