Friday, January 23, 2009

Solar Image Processing: Registax

Actually, there's nothing special about solar imaging if we talk about using Registax. The usual practice for planet works perfectly for solar images.

First of all, you input your AVI. Your AVI should better be in RGB24 or Y800. Y800 is the better choice since it works with less hard disk space. It loads with less memory space too, and with the reduced data size, it works faster too.

Choosing the alignment point is important. Narrow band solar imaging is usually lack of contrast, unless you have a very good sky and a very narrow bandwidth filter. You will want to find a good alignment point where the contrast is maximum. A small and contrasty feature is the perfect candidate. A thin but long feature is bad usually except the both ends.

Automatic processing usually works, but in case where the seeing is very bad, or the final result is blurred due to poor image registration, you will want to disabled automatic processing.

If you have disabled automatic processing, you can choose how to select frames to be stacked. Discarding the poor quality ones are usually good, and you can also discard those frames which a big difference than the reference. Those frames with a big difference are usually a result of poor alignment (registration).

Next you have the stacked raw. Check if it's blur, if so, re-do the alignment or exclude some poor frames with the techniques I mentioned above.

Finally, adjust the wavelet. A good image will usually allow simple sliding the first level all the way to a point before noise become too ugly. If the raws are no good, choose level two or even lower levels.I usually save as BMP and then I will further adjust it with Photoshop/GIMP or whatever software that you love.

On stacking, you can choose the stretch the history in registax, but I didn't recommend it for solar imaging due to uneven illumination and non-uniform bandwidth across the whole field. Stretching the histogram could expose all those issues. We can do this with other softwares for better results.

Next time I shall talk about how to make your b/w image into false color image, and also how to do the final processing like to bring out the prominence in a surface detail exposure, etc. Comment and questions are welcome.

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