From: Alan Friedman <alan@greatarrow.com>

Date: August 31, 2009 7:31:08 AM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Colour Jupiter from Ray [4 Attachments]

Hi Ray,

The histogram shows in the capture window of AstroIIDC - very important tool. It is hard to evaluate the brightness of the image looking at the screen at nighttime. Gain and brightness are the same thing. Gamma (contrast) is the setting that you are referring to, and it is usually best left neutral (at 1.00), though there are times that I fiddle with it a little. Increasing the contrast will lower the brightness of the image, but it will increase the visibility of cloud belt features on Jupiter and this might be an advantage if you attempt to align frames on a feature such as the GRS or a festoon or barge within Jupiter's cloud bands. This advantage does come at the expense of lost information when the contrast is boosted. Sometimes I shoot below 1.00 (down to .90) when imaging solar prominences as the faint parts seem to become more visible as contrast is reduced. 

As I mentioned before, I often shoot at quite high brightness values - 700-950 - as I am usually working at a long focal length and at the limits of the available light for my aperture.

best regards,

Alan

On Aug 31, 2009, at 8:33 AM, Ray Byrne wrote:

Hi Guys,

On Saturday/Sunday I took some movies of Jupiter in pretty bad seeing
but actually better than the last few weeks. Out of them I got one OK
result which I've posted in the photos section on our site. When I
came to do the colour processing (it was in the small hours) I got
muddled-up somehow and and kept getting a mono result. Frustrated and
impatient I sent the LRGB set to my mate Mick Hyde to do the colour
bit for me which is the result you'll see.

Now he uses the same gear as me but being a PC/Windows guy uses the
K3CCD Tools/ Registax combo for capture and processing and remarked
that my LRGB set were very dark. To quote Mick he said " Ray, There
you go. The images were very dark though, I had stretch them with
curves in PS. I think you need to check your histogram whilst
capturing and boost the gain a bit." Two things about this what would
be the equivalent in Astro IIDC of the histogram he's referring to?
and should a fiddle with the gain? As regards the gain I always keep
that set to 1.00 and use brightness instead, but of course the more
you increase the brightness the noisier the resultant image is it
seems, should a adjust the gain? Here are reduced sized files before
processing in PS:

(actually this is the first time I've seen them in daylight they are
very dark)

ATB

Ray Byrne