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.

  1. The CCD... subwidgets available from the XPOSE GUIS on the red and blue side have functions that alter the windowing and binning.
  2. 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
  3. 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. 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.