Windowing and Binning

Windowing and binning methods is different for the blue and red detectors. Windowing and Binning are used to decrease the CCD readout times on both the Red and Blue channels. Below, we describe various methods, their benefits, and possible pitfalls. At the bottom are speed test results for different windowing and binning setups.

On the red side, windowing is not possible. Binning is possible. The pane xy values are always expressed in units of unbinned pixels.

On the blue side, windowing and binning are dependant. When operated without binning (binning factor of 1x1) the maximum value for xy windows is 2048. When the binning factor is N, then the maximum value is reduced to 2048/N. Binning by powers of 2 is essential to success, and if binning is changed, you must window the ccd to the corresponding size. You cannot window the blue mosaic across the two CCDs. To window a section, you will have to window on one of the CCDs. See the windowb section below for details on how to do this.

The CCD... subwidgets available from the XPOSE GUIS on the red and blue side have functions that alter the windowing and binning.
- Binning 1x2 - bins only in the spectral direction. This will also reset the window appropriately. Decreases the readout time.
- Binning 2x2 - bins in both spectral and spatial directions. This will also reset the window appropriately. Decreases the readout time, but adds an image artifact.
- Window full frame mosaic (1x1) - resets to binning 1x1 and full frame mosaic (re-windows to full frame).
- Two amp readout on blue CCD0 (left) - selects only the left most CCD
- Two amp readout on blue CCD1 (right) - selects only the right most CCD
Blue side windowing: windowb is a script that may be used to window the blue side. The script is called windowb and takes four arguments (x, y, w, h). The x and y are the starting pixel and the w and h are the width and height of the desired readout region. You cannot window across the two chips, and the script will complain if the desired window spans both chips.
```
 windowb xpix ypix width height
```
The WIN... subwidgets available from the XPOSE GUIs on the red and blue side allow manipulation of the CCD readout window and binning. The blue side may not be windowed, unless the readout is for a single chip. To bin data on the blue side, "Two amp readout" on the left or right must first be selected. If you try to sub_window the blue side or you try binning without setting "Two amp readout," the blue side crate will be lost after the first readout and will require rebooting. See XPOSE for more information.

Speed Test Results

Wall clock times for a 1 sec exposure. Wall clock times include time needed to erase, expose, and redout the CCDs.

54s - Window Full Frame & 1x1 binning.
54s - Windowed in the spatial direction only (100 pix width) & 1x1 binning
36s - Window Full Frame & 1x2 binning
23s - Window 1/2 Frame & 1x2 binning

Note that time is not saved by windowing in the spatial direction (across columns) on the Blue channel CCD. To save time by windowing, the number of rows read must be reduced.

**LRIS-R Mark IV Readout Times**
Number of Amps	Binning	Readout Time*
4	1x1	54s
4	2x2	24s
2	1x1	97s
2	1x2	55s
2	2x1	65s
2	2x2	39s

*Elapsed time for 0 sec exposure, including erase, expose, and readout phases.