Frame acquisition allows to define how SkyGuard works with the guider camera to capture frames.

 Before setting the acquisition parameters, you must first configure at least one instrument and connect.

To connect the instrument, click on the  button.

 When guider is exposing the acquisition settings are disabled, to change them you must stop exposing

Exposure allows to define the exposure time in seconds. By default the exposure time is set to 3 seconds.

Binning allows to define the pixel binning. By default 2x2 pixels.

Block compression allows to define how the frame will be divided to reduce the amount of memory used. By default the block compression is not used and set to one.

This option is useful with large guiding chip.

Raw image allows to display the raw frame in the current image when this options is unchecked the frame processed by the algorithms is displayed instead.

To see how the algorithm see the guider frame, you can toggle the raw image check box while guiding.

 SkyGuard 32 bits is able to work with frame up to a mega pixels, if your guider camera resolution exceed a mega pixels the following error message will be displayed when start exposing.

To reduce the size of the guider frame there are three tools available:

1. Increase the binning

2. Use block compression

3. Define a sub-frame (cropping)

4. Or any combination of the above

Increase the binning

SkyGuard is able to combine hardware and software binning. That means if your binning settings is not supported by the guider camera SkyGuard will use hardware and software binning together to bin the guider frame according your settings.

 If the guider camera support a max binning of 4x4 pixels and you want to use get 8x8 pixels. SkyGuard will configure the camera with a 4x4 hardware binning and will compute a 2x2 software binning to reach 8x8.

Hardware binning is usually much faster than software binning.

When the software binning is used, the following message box appear:

 SkyGuard computing resolution is 10th of a binned pixel. If a large binning is of any concern for guiding resolution then using block compression or sub-frame may be a better solution.

Use block compression

Block compression is a trick that allow to fold the frame on itself by lowering its size without losing any information nor pixel resolution.

To illustrate how block compression is operating, we took a guider frame of 2048x2048 pixels containing four objects distributed in each corner (A, B, C and D).

With a block compression divider of 2, the guider frame size is divided by 4 leading to eventually a compressed frame resolution of 1024x1024 pixels without loosing any information (objects A, B, C and D are still in the image)

Define a sub-frame (cropping)

Cropping allows to define a sub-frame inside the guider frame to reduce its resolution by losing information and keep the same pixel resolution.

Cropping and block compression gives the same result in term of final pixel resolution but block compression avoid any information loss. To reduce the frame size we recommend using block compression when one wants to keep the all information (pattern) of the raw frame.

Start exposing

Once acquisition settings are correctly defined, the guider camera exposing can be started.

To start exposing, click on the  button.
It should be understood that starting guider exposure does not mean that any correction will be sent to the mount yet.

Frame progressing and guiding error calculation will take place and be displayed however active auto-guiding required to star guiding.

 Fixed pattern noise, if an issue, can be handled using dark frame subtraction. By default SkyGuard uses a 2x2 pixel median filter for removing hot pixels and image local artifacts. If the mount can be moved by SkyGuard (with manual move for instance) but it does not register any motion this is usually a strong indication that hot pixels may overwhelm any guider frame actual astronomical patterns.

Since hot pixels (and other local image artifacts) do not move SkyGuard may fail to detect any image motion.
The median filter 2x2 default setting should be enough to deal with hot pixels, if not it can be increased, larger values lead to slower frame processing.

When start exposing, SkyGuard is checking the configuration to ensure that all actions have been taken to prevent hot pixels and fixed pattern noise issues, if any, as much as possible. If the configuration is not optimal, the following warning message box is displayed:

Using dark frame subtraction to remove hot pixels, especially with an un-cooled camera, may fail while temperature changes since those pixel amplitudes are usually related to the sensor and electronic temperature. We do recommend to use the median filter for processing the hot pixels.

To remove pixels, there is two tool available, the first one is the best :

1. Apply a median filter on the guider output frame in order to remove hot pixels

2. Subtract a dark frame from the guider output frame (see above warning)

To adjust configuration prior starting exposing, you must click "No", to start exposing click "Yes".

When guider camera exposing is running, the  button switch to  button and the  button is enabled.

For each new guider frame the current image background is refreshed, the frame number is incremented, the auto-guiding errors and status, as well as the evaluation of the SNR level are displayed in the HUD.

Stop and Pause exposing

To stop exposing, you can either click  or  buttons.

To pause exposing, click  button.

When exposing is paused, click  button to resume.

Unlike when using the pause exposing button, resuming after having used stopping or disconnecting buttons, SkyGuard will retake a guider reference frame.