Compose: Effortless, Signal Evolution-Tracked Composite Creation and Processing

In conjunction with the Composite module, the Entropy module can be used to boost detail in, for example, Synthetic L+SHO datasets, while availing of signal evolution Tracking. Here O-III was boosted, while Tracking kept noise propagation under control.

The Compose module is easy-to-use, but extremely flexible compositing and channel extraction tool. As opposed to all other software, the Compose module allows you to effortless process, LRGB, LLRGB, or narrowband composites like SHO, LSHO and more composites, as if they were simple RGB datasets.

In traditional image processing software, composites with separate luminance information (for example acquired through a luminance filter, created by a synthetic luminance frame, or a combination of both), require lengthy processing workflows; luminance (detail) and color information needs (or should!) be processed separately and only combined at the end to produce the final image.

Through the Compose module, StarTools is able to process luminance and color information separately, yet simultaneously.

This has important ramifications for your workflow and signal fidelity;

• Your workflow for a complex composite is now virtually the same as it is for a simple DSLR/OSC dataset; Modules like Wipe and Color automatically consult and manipulate the correct dataset(s) and enable additional functionality where needed.
• Because everything is now done in one Tracking session, you get all the benefits from signal evolution tracking until the very end, without having to end your workflow for luminance and start a new one for chroma/color; all modules cross-reference luminance and color information as needed until the very end, yielding vastly cleaner results.
• The "Entropy" module can consult the chroma/color information to effortlessly manipulate luminance as you see fit, while Tracking monitors noise propagation.

Synthetic luminance dataset are created by simply specifying the total exposure times for each imported dataset. With a click of a button, synthetic luminance datasets can be added to an existing luminance dataset, or can be used as a (synthetic) luminance dataset in its own right.

Finally, the Compose module can be used to create bi-color composites, or to extract individual channels from color images.

Usage

Creating a composite is as easy as loading the desired datasets into the desired slots, and optionally setting the desired composite scheme and exposure lengths.

The "Luminance" button loads a dataset into the "Luminance File" slot. The "Lum Total Exposure" slider determines the total exposure length in hours, minutes and seconds. This value is used to create the correct weighted synthetic luminance dataset, in case the "Luminance, Color" composite mode is set to create a synthetic luminance form the loaded channels. Loading a Luminance file will only have an effect when the "Luminance, Color" parameter is set to a compositing scheme that incorporates a luminance dataset (e.g. "L, RGB", "L + Synthetic L From RGB, RGB" or "L + Synthetic L From RGB, Mono") .

The Red, Green and Blue buttons load a dataset in the "Red File", "Green File" and "Blue File" slots respectively. The "Red Total Exposure", "Green Total Exposure", "Blue Total Exposure" sliders determine the total exposure length in hours, minutes and seconds for each of the three slots. These values are used to create the correct weighted synthetic luminance dataset (at 1/3rd weighting of the "Lum Total Exposure"), in case the "Luminance, Color" composite mode is set to create a synthetic luminance from the loaded channels.

Loading an dataset into the "Red File", "Green File" or "Blue File" slots will see any missing slots be synthesised automatically if the "Color Ch. Interpolation" parameter is set to "On". Loading a color dataset into the "Red File", "Green File" or "Blue File" slots will automatically extract the red, green and blue channels of the color dataset respectively.

There are a number of compositing schemes available, some of which will put StarTools into "composite" mode (as signified by a lit up "Compose" label on the Compose button on the home screen). Compositing schemes that require separate processing of luminance and color will put StarTools in this special mode. Some module may exhibit subtly different behaviour, or expose different functionality while in this mode.

The following compositing schemes are selectable;

"RGB, RGB" simply uses red + green + blue for luminance and uses red, green and blue for the color information. No special processing or compositing is done. Any loaded Luminance dataset is ignored, as are Total exposure settings.

"RGB, Mono" simply uses red + green + blue for luminance and uses the average of the red, green and blue channels for all channels for the color information, resulting in a mono image. Any loaded Luminance dataset is ignored, as are Total exposure settings.

"L, RGB" simply uses the loaded luminance dataset for luminance and uses red, green and blue for the color information. Total exposure settings are ignored. StarTools will be put into "composite" mode, processing luminance and color separately but simultaneously. If not Luminance dataset is loaded, this scheme functions the same as "RGB, RGB" with the execption that StarTools will be put into "composite" mode, processing luminance and color separately yet simultaneously.

"L + Synthetic L from RGB, RGB" creates a synthetic luminance dataset from Luminance, Red, Green and Blue, weighted according to the exposure times provided by the "Total Exposure" sliders. The color information will consists of simply the red, green and blue datasets as imported. StarTools will be put into "composite" mode, processing luminance and color separately yet simultaneously.

"L + Synthetic L from RGB, Mono" creates a synthetic luminance dataset from Luminance, Red, Green and Blue, weighted according to the exposure times provided by the "Total Exposure" sliders. The color information will consists of the average of the red, green and blue channels for all channels, yielding a mono image. StarTools is not put into "composite" mode, as no color information is available.

On synthetic luminance generation

For practical purpose, synthetic luminance generation assumes that, besides possibly varying total exposure lengths, all other factors remain equal. E.g. it is assumed that bandwidth response is exactly equal to that of the other filters in terms of width and transmission, and that only shot noise from the object varies (either due to differences in signal in the different filter band from the imaged object, or due to differing exposure times).

When added to a real (non synthetic) luminance filter source, the synthetic luminance's three red, green and blue channels are assumed to contribute exactly one third to the added synthetic luminance. E.g. it is assumed that the aggregate filter response of the individual three red, green and blue channels, exactly match that of the single luminance channel.

Channel assignment and coloring

As of StarTools 1.6, channel assignment does not dictate final coloring. In other words, loading, for example, your SHO dataset as RGB, no longer locks you into that choice.

Uniquely, thanks to the signal evolution Tracking engine, the Color module allows you to remap the channels at will, even far into your processing.

So, if for example you wish to switch your SHO imported dataset to a OHS rendering instead (or even complex channel blends), you can do so in a couple of clicks. The same goes for a HOO bi-color. Also see the Color module documentation for more information.

Popular coloring

Popular narrowband composite coloring

Hubble / HST / SHO

The Hubble Space Telescope palette (also known as 'HST' or 'SHO' palette) is a popular palette for color renditions of the S-II, Hydrogen-alpha and O-III emission bands. This palette is achieved by loading S-II, Hydrogen-alpha and O-III ("SHO") as red, green and blue respectively. A special "Hubble" preset in the Color module provides a shortcut to color rendition settings that mimic the results from the more limited image processing tools from the 1990s.

H-alpha and O-III bi-color

A popular bi-color rendition of H-alpha and O-III is to import H-alpha as red and O-III as green as well as blue. A synthetic luminance frame is then created that only gives red and blue (or green instead of blue, but not both!) a weighting according to the two datasets' exposure lengths. The resulting color rendition tends to be close to these bands' manifestation in the visual spectrum with H-alpha a deep red and O-III appearing as a teal green.