ImageIntegration can't integrate 2 images?

[nunopc]

Hi,
When I try to to integrate 2 images with Image Integration I get this message:

"Cannot execute instance in the global context.
Reason: This instance of ImageIntegration defines less than three source images."

Why it isn't possible to integrate 2 images?
Thank you and best regards,
Nuno

[aworonow]

ImageIntegration, per se, can do some fancy statistics to determine the value to assign to each pixel (e.g., Winzorized Mean). From just two images, however, about the only relevant statistic one can compute is the mean (average). If you align the two images (using DynamicAlignment) then just average the two images using pixel math: (Image1+Image2)/2. Averaging even two similar images provides some noise reduction ( 1/sqrt(2) ), so it's probably worth doing.

Cheers.

[pfile]

you can also just add one of the images twice to ImageIntegration.

rob

[aworonow]

Probably want to double-up on both frames, so the average is correct. Also be sure to set "No Rejection."

Alex

[nunopc]

Thank you for your replies.
Both images were already calibrated, cosmetized and registered.
I ended up copying the 2 images and do the integration of the 4 in pixinsight.

On the other hand I also tried to do the integration step in DSS (average):
- It works on 2 images.
- Got more SNR in the result: compared to average in PI.
- Got better results in cosmetic correction.

I would appreciate your comments, because I'm am still convinced that I'd better leave the integration step to DSS, though I'd like to keep it in PI...

Thank you and best regards,
Nuno

[ChoJin]

did you assign any weight on your images with PI?

[nunopc]

Yes: "Noise evaluation".

[Andres.Pozo]

[...]
On the other hand I also tried to do the integration step in DSS (average):
[...]
- Got more SNR in the result: compared to average in PI.
[...]

The registering process of DSS uses a worse interpolation algorithm than PixInsight. When registering the images DSS blurs the images more than PI. This blur reduces the noise of the images and the apparent effect of a better SNR in DSS that PI. This SNR improvement is at the expense of bigger stars and less fine details. There are better tools in PI for noise reduction than blurring the image by a bad interpolation.

Some time ago I made a comparison of PI with another application that has the same behavior than DSS:
http://pixinsight.com/forum/index.php?topic=6065.msg41157#msg41157
(Please, click on the image in that link to watch the animation).

[nunopc]

Hi Andres,
Thank you for your reply. It makes sense and helps me deciding a long time dilema and which way to go.
Still what would be your advice to integrate 2 images in PI? I can always duplicate each image and integrate the four images. But if I can circumvent the PI limitation this way, why doesn't PI integrates 2 images using this method automatically? Is there any downside to it that PI is avoiding?