Image capture and display controls
Image display control page
These controls affect the display of the currently focussed
image. The image scaling factor slider bar changes the scaling
factor for the image intensity from 1 to 2000. Note that the
response of the slider is logarithmic rather than linear so that
changes in intensity appear more or less linear to the eye with respect
to the position of the slider (the eye has logarithmic response).
The intensity bias varies from 0 to 65535; this bias is subtracted from
the pixel intensity during display. As for the intensity slider,
the response of the bias slider is logarithmic. If exact values
for the scale and bias are required, they can be entered in the edit
boxes to the right of the sliders.
Clicking "Autoset contrast" causes Pyxis to evaluate the image
histogram in the central part of the image and determine "optimum"
display parameters based on the histogram. When an image is first
captured and automatically displayed, the scale and bias settings are
selected using the same criteria (if "autoset contrast" is checked in
the acquisition settings). "Auto sky subtraction" estimates
the planar component
of the sky background and subtracts it from the image.
Clicking on the coloured palette bars applies the associated palette to
the image. This is useful for quickly changing between different,
frequently used palettes (e.g. grayscale and blackbody). The
palette files associated with the four "quick-select" palettes are;
"QuickPalette1.pal, QuickPalette2.pal, QuickPalette3.pal,
QuickPalette4.pal". These palette files may be edited so that
Pyxis loads your preferred set of custom palettes on startup. See
"Palettes" for more information. Note
that changes to these files will not appear on the coloured
palette bars until Pyxis restarts.
The image displayed to the left of the quick palette selection control
is a 10X zoomed view of the vicinity of the cursor on the image.
Acquisition
settings
Integration time: The
integration time is either the time from clearing to reading the CCD,
or the time the shutter is opened when a shutter is used. The
shortest practical integration time using a Uniblitz shutter is 50 ms.
Frame delay: This is the time
to wait between the end of reading one frame and the beginning of
integration of the next frame. This is useful for long time-lapse
image sequences or to allow the Peltier cooler to recover the CCD
temperature between frames (in the case where the Peltier cooler is
shut down during readout).
Number of frames: The
number of frames to capture in one sequence.
Clearing scans: The
number of full image area clears to perform before the integration
period of each image frame.
Open each frame in a new window:
Toggles whether each newly captured image is displayed in a new child
window or whether the last opened child window is used. It is
preferrable for reasons of speed to uncheck this option.
Disable window close prompt:
If the number of child windows open equals the maximum number of
windows that should be open, and if the previous option is checked,
then the acquisition of a new image will cause the oldest window to be
closed to allow for the new child window. Unless this option is
checked, then a prompt will appear warning the user that any changes in
the image to be closed will be lost. Check this option to avoid
this prompt from appearing.
Turn off cooling during readout:
Selecting this option turns off the high-power Peltier cooling supplies
during readout of the CCD. With the current switch-mode supply,
turning off the Peltier power results in a readout noise reduction at
the output of ~2-3 electrons. It is recommended that this option
be checked.
High thread priority:
Gives the image acquisition thread highest priority in the
application. It is recommended that this option always be checked.
Enable shutter:
Determines whether the shutter is being used in the exposure.
When acquiring dark frames this option should be unchecked.
Dispaly images:
Determines whether captured images are immediately opened and
displayed. For example, this option may be selected when a series
of fast exposures is acquired to increase the frame rate.
Auto-set contrast/intensity:
Automatically calls a routine that uses a histogram of the central part
of the newly captured frame to determine optimum display bias and
intensity scale. Normally this would be checked, however in
certain cases it is useful to use a fixed bias and intensity for each
image so that changes can be readily seen from frame to frame.
Dark frame file: A dark
frame file can be selected to correct for the CCD thermal count.
The"Apply dark frame correction" box must be checked for the dark frame
correction to be automatically applied on frame capture.
Apply flat field correction:
A flat-field frame file can be selected to correct for pixel
sensitivities in the CCD.
The"Apply flat-field correction" box must be checked for the flat-field
correction to be automatically applied on frame capture.
Image descriptors
File prefix: The prefix part of
the save file name.
File postfix: This is a
numeric extension that is always appended to the file prefix. An
underscore is placed between the file prefix and the numeric
postfix. If "Increment postfix" is checked, then the numeric
extension is incremented every time a new image is captured. The
complete filename consists of <file prefix>_<postfix
#>.<file type extension>, where the file type extension is
either "fit", "pxi", "bmp" or "png", depending on what format the file
is saved as.
Increment postfix: When
checked, the postfix number is incremented every time an image is
acquired.
Processed file postfix:
If the image is to be processed prior to saving (i.e. processing
involves one or both of dark field and flat frame correction) then the
file name consists of, <file prefix><processed file
postix>_<postfix #>.<file type extension>
Save processed image: If
checked, the image is processed and only the processed image is saved.
File format: The format used to save the file.
Description: A
description of the image.
Filters: Filters used to
obtain the image. Check "Apply from filter wheel" to
automatically apply the filter description from the current filter
selected using the filter wheel rotator.
Subframe selection
The captured CCD subframe coordinates may either be entered directly on
this form or selected by dragging a selection frame on a previously
captured image (see Main form). The
full frame coordinates can be restored by clicking the "full frame" icon in the
toolbar.
Filter wheel control
This page controls operation of the filter-wheel rotator built into the
Pyxis power supply. The current software only supports a filter
wheel with 6 positions. It is assumed that the filters are placed
in the following positions; (1) blue bandpass filter, (2) green
bandpass filter, (3) red bandpass filter, (4) not defined, (5) clear,
(6) infrared cut (i.e. luminance). The actual filter labels can
be changed to reflect your own system by editing the appropriate boxes
in "Filter Labels".
The filter controller does not have a means to determine the absolute
filter position, it only uses a single sensor to determine the relative
position index on the filter wheel. This means that when the
system is powered up, the actual filter position must first be entered
manually for the filter positioning to work correctly. Enter the
filter postion in the "Current filter position" box, then click the
radio button corresponding to the current filter position. After
this, clicking any of the other filter position radio buttons should
rotate the filter wheel to the correct position. If this does not
work, manually step the filter wheel by using the "full-step" and
"half-step" buttons until the filter-wheel reaches the nominal
position. The filter wheel rotator should operate correctly after
this procedure.
Temperature and power control
Place system in standby mode:
Turns off the Peltier cooling supplies and the bipolar analog supplies
to conserve system power.
Send target CCD temperature:
Upload the target CCD temperature for cooling the main imaging CCD.
Read CCD temperature:
Downloads the CCD temperature of the main imaging CCD.
Power on/off CCD TE cooler:
Turn on/off power for the main imaging CCD Peltier cooler.
Read battery voltage:
Downloads the voltage of the DC input power line.
Target CCD temperature:
The temperature in degrees Celcius to which the Peltier cooler feedback
loop attempts to regulate.
CCD temperature read period:
The period between downloads of the CCD temperature if continuous
monitoring by the host is desired.
Periodically read CCD temperature:
If checked the main CCD temperature will be periodically downloaded and
displayed. It is recommended that this option be disabled if
guiding is enabled.
Calibration frames
Dark frame subtraction and flat fielding of an image can be performed
immediately from this form. When processing multiple files it is
much easier and faster to use the multiple
file processing utility.