 NexImage : Tips for Advanced Users
The NexImage is a webcam that has been customized for planetary imaging. And it does an outstanding job, offering a compact ready-to-go camera and all the software necessary to take great planetary images, as seen on this site. But like all webcams, the NexImage can be optimized to work even better if you are interested in doing so. Below is a description of how to optimize the Celestron NexImage to get the very most out of your camera.
A good online resource for NexImage is the NexImage Yahoo Group.
Celestron's NexImage Solar System Imager is remarkably similar to the Philips ToUcam Pro, at least on the inside. Amateur astronomers have determined how to modify the ToUcam hardware for long exposure imaging and how to modify the internal settings for improved image quality. These same tweaks can be made to the NexImage camera and some information on how to do this is given below.
RAW Color Mode
There are three aspects of the default operation of the ToUcam Pro (and NexImage) that can cause the image quality to be degraded:
- The color information in the image is reformatted, resulting in a small loss of detail.
- The image is compressed to reduce the bandwidth to the PC.
- The default image processing settings can result in over-bright colors and loss of fine detail.
Philips and Logitech webcam owners have determined how to modify the internal settings of the camera (via a software application) to address these issues. The tweaks for the ToUcam Pro also work for the NexImage camera and do improve the resulting images substantially. Etienne Bonduelle's Astro Bond site has an excellent description of how to make these changes, which are completely reversable. The pertinent details of and notes about that process are included below.
Modifying the Settings
Warning: Although this process is reversable, care should be taken when following the instructions to make sure that no damage is done. Celestron did not develop this process or the applications used to make the modifications -- the camera is your own responsibility.
- Download and install the application to modify the camera:
http://www.burri-web.org/bm98/stuff/wcrmac-1.0.79.zip
- Download the latest macros and copy them into the macro folder for WcRmac:
http://astrosurf.com/astrobond/BERaw.zip
- Run an application that accesses the webcam. K3CCDTools or AMCAP is fine.
- Run WcRmac, connect to the camera, and click on "get current and save as" under the binaries tab to save your NexImage's current config.
This is important in order to restore your camera to the original settings.
- Select the "Set Color RAW mode" under the Macros tab and click on "Run checked."
- Go back to your webcam application and in the camera control properties window, set the defaults back to factory settings.
Using RAW Mode
Now you're capturing images in raw mode and the preview won't show the colors correctly (unless your application supports it). To capture in raw mode:
- Capture the video to an AVI as normal. You must keep the frame rate at 5fps and you must not use RGB24 mode or else compression will be re-enabled. Use IYUV or I420 mode.
- Load the AVI into AviRaw (http://arnholm.org/astro/software/aviraw/). Select "Raw Color" and click on BG or RG to properly display the colors. If the colors do not look right, then try a different setting. Leave the processing at "11-DeBayerToRGB".
- Use AviRaw's "Save As" menu to save the converted AVI to a new file.
- Load and process the new AVI in Registax or the image processing package of your choice.
Restoring the Original Settings
To restore the NexImage camera to the original settings:
- Run an application that accesses the webcam. K3CCDTools or AMCAP is fine.
- Run WcRmac and connect to the camera.
- From the Binaries tab, select your saved binary with the original settings and click on "Load into cam" to restore them.
- Go back to your webcam application and in the camera control properties window, set the defaults back to factory settings.
Important Notes
- Compression will be re-enabled and will stay enabled if you change the frame rate away from 5fps or if RGB24 mode is used. There may be other settings that cause compression to turn back on. The only way to disable compression is to use the "restore factory defaults" button in the camera properties window. When compression is enabled in raw mode, there will be corruption in the color information and pixellation will be seen in some areas of the image. It is sometimes a subtle effect, so it may be best to restore factory defaults at the beginning of each session.
- The debayering algorithm (raw conversion) differs from application to application and so you may want to try a few methods before deciding which to use.
- Autoguiding applications like GuideDog may not yield accurate results when used in raw mode. It is easy to undo these changes, so I recommend switching back to the original settings when using applications that process the image directly.
Optimized Color Mode
Optimized color mode is a tweak to the camera's internal settings similar to RAW color mode. However, only the default levels are changed with this mode and so compression and color channel formatting can still cause some image degradation. The process for making the modification is the same as RAW color mode except that a different macro is used. See the Astro Bond pages for more details on this mode.
Long Exposure Modification
Webcam owners have modified their cameras so that exposures are controlled directly via the parallel port instead of using an automatic frame rate. This allows exposures of arbitrary length to be taken, making the camera usable for imaging deep-sky objects. Some acquisition and processing packages like K3CCDTools support these long exposure modifications.
Freddy Diaz is a NexImage owner who has modified his camera for long exposures. The modifications are fairly simple and are outlined on his web page.
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