splitting & recombining channels

[lucchett]

Juan, that was exactly my first question:
split channels: channel extraction

combine channels: using the above three files give me an error (grey images)

I've found a work around for RGB: I duplicate RED, make it RGB and select it as target, then select the three gray splitted channels.

But don't know what to do for HSV..

Many thanks,
andrea

Howdy!

Sorry for not being responsive, but 1.5.2 has all of me right now.

To split channels: ChannelExtraction
To combine channels: ChannelCombination

In general, don't use LRGCombination for this task. This tool is strictly intended to perform LRGB combinations, as its name says. It applies nonlinear transformations which is not what you want.

You can also recombine RGB images using PixelMath, but ChannelCombination is easier.

Note that ChannelCombination can be applied to previews. This means that you can split HSV channels (for example), alter them, then try out the result on a preview (of an image with the same dimensions as the channels; you can either define a preview on the original image or use NewImage to create a new one of the appropriate size).

To split RGB channels, you have a dedicated menu item: Image > Extract > Split RGB Channels, also available on the Image tool bar.

Splitting RGB channels, registering them with StarAlignment and recombining, is in general the best way to fix lateral chromatic aberration. If the aberrations are really wild (so that they can't be described as translation + rotation + scaling), you may consider using DynamicAlignment instead, which allows for arbitrary deformations of any kind.

[Juan Conejero]

Hi Andrea,

the goal is to extract the luminance channel from one rgb, combine it with other luminance data and then make the LRGB.

To do this you don't need to split the RGB channels. These are your steps:

- Extract the luminance. For example, use Image > Extract > Luminance from the main menu.

- Process this luminance as necessary (combine it, etc.)

- Open the LRGBCombination tool. Select your new luminance in the L slot. Uncheck (disable) the R, G and B slots. Leave the rest of parameters with their default values. Now apply the process to your RGB image, and voilà

[Astrocava]

Hi Sergio

I can say that in my DSLR images, more frecuently when shotting near the horizon, channels are not perfectly aligned. I usually have red arcs only in one side of the stars. When I perform the new alignment, i have complete colour arcs in my stars.

This is also a typical problem where StarAlignment usually does a nice job. Color misalignment is due to atmospheric color dispersion in this case. This is a vertical displacement (normal to the horizon line) between channels, combined with a scaling effect (actually a vertical chirping effect, especially if the FOV is large). Since this can be described as a homographic transformation, StarAlignment works nicely (at least in all cases I've seen so far).

That's what I do, but I use LRGBcombination instead ChannelCombination.

  . Will need to reprocess some images, unless if L box is not checked it works like ChannelCombination.

Sergio

[Juan Conejero]

Hi Andrea,

I duplicate RED, make it RGB and select it as target

Clever

Note that you can also apply LRGBCombination to your RGB image directly, as I explained in my previous post.

But don't know what to do for HSV

- You start with a RGB image.

- Use the ChannelExtraction tool to obtain the H, S and V components.

- Process them as desired.

- Open ChannelCombination. Select the HSV space on the left panel. Select your H, S and V images in their corresponding slots (ignore the Target option). Apply the process to your RGB image.

[Juan Conejero]

That's what I do, but I use LRGBcombination instead ChannelCombination.

  . Will need to reprocess some images, unless if L box is not checked it works like ChannelCombination.

If you don't substitute the luminance and don't modify other parameters (weights, MTF, saturation, etc.) then the process does the same as ChannelCombination. So it seems you don't need to repeat your work

[Astrocava]

 8) Nice!