Testing the new DMx WB Auto white balance function in AstroDMx Capture.
This improved version of the DMx Auto WB function with automatic brightness compensation will be in the next release of AstroDMx Capture for all platforms, as will the 16-bit format RGB48 for cameras that offer it, such as Altair and Touptek cameras.
When capturing RAW data with cameras such as Altair and Touptek, The preview and captured images have a green tint as we have mentioned previously. To some extent, this can also happen with Atik colour cameras.
Altair describe this as normal and what would be expected when capturing true RAW data. The green tint can be removed in post processing.
However, as we have pointed out previously, sometimes the preview image is especially important, for example, for outreach work. Moreover, if one is doing live-stacking by combining AstroDMx Capture with DSS Live, it would be desirable to have white balanced data being live-stacked.
Nicola has solved this problem in two ways.
- Implementation of RGB48 capture. RGB48 is a 16-bit colour format for which there is a white balance control as there is in RGB24, the 8-bit format. The RGB48 format is generally not available in other capture software, and is not available for many camera types.
- Implementation of DMx Auto WB for RAW16 and RAW8 captures which works with Fully debayered data. The DMx Auto WB can be turned on or off for the preview and it can also be turned on or off for saving.
RGB48 for a camera such as an Altair or a Touptek can be selected when the camera is connected.
The format can also be changed from within the program when it is running.
This mode has a one touch white balance.
We used an Altair GP-CAM 225C camera at the focus of a Skymax127 that was mounted on a Star Discovery AZ mount. Using AstroDMx Capture for Linux, a 2000-frame SER file was captured of the Moon, which during the current lunation, is extremely low and was only just visible over the mountain opposite our site. As a consequence, seeing was very poor due to the low altitude of the Moon and the heat rising off the mountain. Nevertheless, conditions were good enough to perform a test.
Animation showing AstroDMx Capture streaming lunar data with the DMx Auto WB turned on and off
It can be seen that when the DMx Auto WB is on, the image loses its green tint and retains its brightness because the Brightness Compensation is turned on. Also, when the DMx Auto WB was on we set it to apply to save data.
AstroDMx Capture for Linux capturing lunar data as a 2000-frame SER file
Final image of the Posidonius, Hercules, Atlas, Mare Serenitatis region of the Moon
A closer look at the DMx Auto WB function
We focused a refractor fitted with an Altair GP-CAM 225C on the top of an electricity transformer pole across the valley, using RAW16 with AstroDMx Capture for Linux
There are three images in this animation.
- DMx Auto WB OFF (This shows a green tint)
- DMx Auto WB ON (Just for the display)
- DMx Auto WB ON (For display and applied to saved data)
When the DMx Auto WB is on, the Brightness compensation is turned on. If this is turned off, the white-balanced image will be dimmer than the un-white-balanced image.
The histogram shows the histogram of the data to be saved and is shown in closeup in the following image.
From Left to Right:
- DMx Auto WB OFF
- DMx Auto WB ON but not applied to saved data
- DMx Auto WB ON and applied to saved data.
The DMx Auto WB function is there for the imager to use or not, and if it is used, it can be applied to the saved data as well as the preview, or it can just be applied to the preview.
