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.
On the Blue side
- 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.
Blue Channel
- 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.