johnpane
Well-known member
One-shot color images have inevitable chromatic misalignment, caused by some combination of the optics and atmospheric dispersion.
Some users attempt to correct for this in the integrated image using ChannelMatch. This does not work ideally because the chromatic errors vary across subframes (e.g., atmospheric dispersion varies as altitude changes during subframe collection), so once the image has been integrated the chromatic errors cannot be accurately corrected. Moreover, the chromatic errors are a combination of linear offsets (from atmospheric dispersion) and radial scaling (from the optics), requiring careful adjustment of both scale and offset.
Ideally, the corrections wold be done on individual subframes, using the full capabilities of StarAlignment. The user could separate the channels of each subframe, align the red and blue to green, then recombine the channels. That could be scripted to avoid the tedium of repeating these steps for each subframe, but I think this approach would not flow through in a CFA Drizzle workflow.
I propose that StarAlignment be enhanced to offer an option for OSC images, where it separately aligns each of the three color channels of each target frame to the reference frame (the green channel of the reference frame if it is a color image such as one of the subframes). StarAlignment could store all three transformation matrices in the Drizzle files so that DrizzleIntegration could replicate the channel alignment during the CFA Drizzle process.
Some users attempt to correct for this in the integrated image using ChannelMatch. This does not work ideally because the chromatic errors vary across subframes (e.g., atmospheric dispersion varies as altitude changes during subframe collection), so once the image has been integrated the chromatic errors cannot be accurately corrected. Moreover, the chromatic errors are a combination of linear offsets (from atmospheric dispersion) and radial scaling (from the optics), requiring careful adjustment of both scale and offset.
Ideally, the corrections wold be done on individual subframes, using the full capabilities of StarAlignment. The user could separate the channels of each subframe, align the red and blue to green, then recombine the channels. That could be scripted to avoid the tedium of repeating these steps for each subframe, but I think this approach would not flow through in a CFA Drizzle workflow.
I propose that StarAlignment be enhanced to offer an option for OSC images, where it separately aligns each of the three color channels of each target frame to the reference frame (the green channel of the reference frame if it is a color image such as one of the subframes). StarAlignment could store all three transformation matrices in the Drizzle files so that DrizzleIntegration could replicate the channel alignment during the CFA Drizzle process.