Noisy image with Orion SSAG

[GoogleCodeExporter]

What steps will reproduce the problem?
1. A fresh install of PHD 2.4.1 on either Windows XP or Windows 7.
2. Reboot laptop for good measure.
3. Start PHD, and configure to use Orion SSAG using "On Camera" mount setting.
4.  Make sure dark frame library is not used and noise reduction is set to 
none.  Camera gain is set to default of 95.
5. Start looping 2.5s exposures.

What is the expected output? What do you see instead?
The image appears much noisier than with PHD1 regardless of the screen stretch 
setting.

What version of the product are you using? On what operating system?
I've reproduced the behaviour in both Windows XP and Windows 7.

Please provide any additional information below.
In Windows 7 I've tried both the SSAG v2 and v4 drivers and the effect is the 
same.  I've also gone through all the older versions (including development 
releases) and have discovered that up to PHD 2.2.2d the image appears the same 
as in PHD1.  From PHD 2.2.2e onwards the image is much noisier. I have tried 
enabling dark frames but this does not help.  I've enabled 2x2 median noise 
reduction which helps a little.  3x3 noise reduction is best, but this does 
reduce the number of dimmer guide stars available.  I've attached a document 
showing the difference, and with the settings I used which were the same in 
both versions.

Original issue reported on code.google.com by si...@caracol.co.uk on 4 Jan 2015 at 5:14

Attachments:

• ssag.docx

[GoogleCodeExporter]

Simon,

Prior to version 2.2.2e there was a bug in the calculation of the black and 
white points for the screen display gamma stretch. The difference is most 
pronounced when there is very little dynamic range, like your tests with the 
lens cap covered.  The bug caused the older versions to use an artificially 
wide dynamic range, hence a less pronounced histogram stretch and a darker 
display.

You will find that the camera data is exactly the same across versions and has 
not changed. You can confirm this by doing File => Save Image which will save 
the raw camera data (not the stretched version of the data that is displayed on 
the screen) and look at the histograms in a fits image viewer.

You can get a darker display on the screen (similar to what you saw in 2.2.2d 
and earlier) by sliding the gamma slider to the right.  The underlying data 
from the camera is the same, no more and no less noisy.

Andy

Original comment by andy.gal...@gmail.com on 4 Jan 2015 at 6:59

• Changed state: Invalid

[GoogleCodeExporter]

 Hi Andy,
Thank you for your reply. So far I haven't tried the latest version
on the stars as the weather hasn't been cooperative.  I did try
moving the gamma slider all the way over to the right which did make
the image darker, though it was just as noisy, and still very
different to older versions.  However, based on what you've said
this may be expected behaviour given the lack of signal with the lens
cap in place.  Once I have some clear skies to work with I'll give
that a try and report back, though looking at the forecast it's
likely to be a week or two.  In the meantime I'll try saving an
image from each version to compare the difference, as you've
described.
RegardsSimon  

Original comment by si...@caracol.co.uk on 4 Jan 2015 at 10:07

[GoogleCodeExporter]

Hi Andy,

This is just to confirm that I have just saved FIT files in PHD 1.14 and 2.4.1 
to compare the histograms.  You are quite right, they both appear very similar. 
 I shall look forward to giving version 2 a proper test under the stars.

Original comment by si...@caracol.co.uk on 5 Jan 2015 at 1:20