Astro photo processing instructions here...
Celestron C-8 SCT
Gary Honis modified Canon 450D (Baeder Mod)
MonoMods monochrome Canon 450D (Debayered, Baader filter, LPF1 removed)
ONAG On-Axis Guider
Starlight Xpress Lodestar Autoguider
Canon EF 200mm f/2.8L II USM
Olympus Zuiko 50mm f/1.8
Scopes: Meade SN6, 10" Dob, Meade LS6, 5" reflector, 8" reflector, 102GT
Mounts: LXD75 and LXD55
Camera: SBIG 8300M, Baader 7nm Ha, OIII, SII, LRGB
Personal website: http://www3.asiaa.sinica.edu.tw/~whwang/
Astrobin gallery: http://www.astrobin.com/users/whwang/
Quote:I use Photoshop to combine my stacks (I don't usually use different sub length, but I usually have stacks from several nights I need to combine). In Photoshop, you weight the stacks by assigning the opacity to that layer of the stack based upon how much of the total exposure time it represents of all of the layers below it. So, if I were combining your stacks in Photoshop, I would weight them as follows (I'll put the shortest subs on the bottom, but it doesn't matter the order).
Quote:It would be nice to find software which can automatically weight the subs based on SNR. It seems Theli does it, but it looks like you need to be a PHD to install and use it.Does anyone know stacking software which stacks based on weight derived from snr?
Quote:Hi everyone,It is correct that the images need to be weighted proportionally to their integration time. However, the effect of different ISO needs to be taken into account too. An image taken with higher ISO appears to have higher pixel brightness, so its weight in the stacking process would be artificially elevated.So, the proper weights should be proportional to the integration times, and inversely proportional to the ISO.Cheers,Wei-Hao
Quote:Scott, can you describe click-level steps to combine/weigh stacks in Photoshop?
Quote:If one were to do this in ImagesPlus how would it be done? Thanks
Quote:i'm new to photoshop and i'm wondering how to process in this scenario. do i simply add my layers (curves, levels, hue, etc.) on to the 'top' layer? in other words, do i just 'process' the top layer? do i merge them at some point? please excuse my ignorance! just started out using that program...
Quote:Hi Wei-Hao -After I made that prior post, I realized I was off on a different tangent- my apologies for that. I agree with you that the issue is SNR. Correct me if I am wrong. In your example of equal exposure but unequal ISO, both images start out with identical SNR. The ISO 200 has amplified the signal by 2, and the noise by 2, so the S/N is 2S/2N = S/N. Would this be correct so far?If I have two images that have the same SNR, wouldn't I want to weight them equally?
Quote:Of course, your ISO 1,000,000 camera would end up clipping, so you probably should use a lower ISO.:-)
Quote:Quote:Of course, your ISO 1,000,000 camera would end up clipping, so you probably should use a lower ISO.:-) That's true. You know what? I found my most comfortable ISO with Nikon D800 is 200, not the more commonly used ISO 800 or 1600. I have some images taken in the past month. Once I finish the processing, I will share it with people here.
Mach1GTO / G11/G2 (stock) / AT6RC / AT10RC / TMB92SS / Astrodon 50D / STT-8300M / FW8G-STT / PixInsight / etc, etc. Astrobin - Flickr