Staralignment creates transparent images

[Nocturnal]

Hi,

I tried to star align 4 TIFF files Neil Flemming uploaded here:

http://www.flemingastrophotography.com/astropics/interim/M82.zip

When I use Staralignment it seems things work fine:

StarAlignment: Processing view: _4_20090520003149
_1_20090520003020:
Extracting CIE L* component: 100%
Structure map: 100%
Detecting stars: 100%
14 stars found.
_4_20090520003149:
Extracting CIE L* component: 100%
Structure map: 100%
Detecting stars: 100%
24 stars found.
Matching stars...
13 putative star pair matches.
Performing RANSAC...
13 star pair matches in 73 RANSAC iterations.
Root mean square error:
drms  :  0.403 px
Peak errors:
dXmax :  0.586 px
dYmax :  0.679 px
Transformation matrix:
     +0.9961     -0.0016     +0.9230
     -0.0011     +0.9959     +0.3642
     -0.0000     -0.0000     +1.0000
Generating registered image: _4_20090520003149_registered
Homographic Projection / Bicubic Spline Interpolation: 100%
Registration successful.
0.937 s

but the resulting image is transparent (shows grey/white blocks). Let me know if you can't reproduce this.

PS I asked Neil's permission before posting this.

[Nocturnal]

Neil further mentioned this:

You might want to mention that the TIFs came from "Deepsky
Imaging".  Seem to be some sort of compressed format. 
Windows Picture and Fax Viewer seem to handle them, but not
many other products.      ...Neil

PI loads them fine but somewhere the staralignment goes wrong.

[Juan Conejero]

Hi Sander,

You have detected a (minor) bug in StarAlignment. It will be fixed in version 1.5.x (due this week).

Each of these images have an alpha channel, which is useless because it defines no transparency (all alpha pixels = 1). The bug is that StarAlignment is setting alpha channels to pure black in all registered images, despite the original alpha channel contents. This is why they look completely transparent. But of course, the registered images have their RGB channels intact.

Workaround: Remove the alpha channels. You can do this after running StarAlignment:

- Define a ExtractAlphaChannels instance (Image category): Channels: "All alpha channels", Mode: uncheck "Extract alpha channels", check "Delete alpha channels". Apply this instance to all registered images (you can use an ImageContainer).

Thanks for catching this one

BTW, what is the purpose of registering these (webcam?) images?

[Nocturnal]

Hi Juan,

thanks for checking this out so quickly. It was merely an exercise because DeepSkyStacker couldn't handle the files either. This was discussed in a DSS thread today that you probably haven't seen yet.

As I understand it these are subs captured from a Mallincam. Neil wants to use DSS Live to integrate the images, well, live during outreach star parties I think. So there's no *need* for PI to deal with these images but I was curious to try and poof! things broke

Thanks for fixing this but there's no urgency.

[Juan Conejero]

thanks for checking this out so quickly

You know, SA is one of our crown jewels, so each time I see the words "StarAlignment" and "bug" in the same paragraph, I jump like a spring