quadformat: Format for multi-amplifier CCD images
Package: quadred
Description
CCDs may be readout from multiple amplifiers at the same time to increase the readout speed. This produces multiple images of rectangular regions in the full CCD exposure. The amplifier readout images may be recorded in various ways. One way is as extensions in a multiextension FITS file. This type of format can be reduced using the MSCRED package.
Another way is to paste the regions into a single two-dimensional image. This, along with specific keywords to describe the locations of the regions, constitutes the quadformat format described here and used by the QUADRED package. The term "quad" originates from the possibility of using four amplifiers in quadrants but the format also includes any other number of amplifiers.
It is important to realize that this is a special format only as long as the overscan or prescan data is included in the image data. Once this information is used and removed as part of the processing the resulting image can be treated in the same way as a single amplifier CCD image. However, the image can still contain the format keywords allowing the regions from the different amplifiers to be identified and extracted as needed.
The quadformat consists of a single 2D image for a single CCD exposure. The image storage format may be any standard image type such as imh or fits. Within the image are regions containing the CCD pixel data and regions containing overscan or prescan, which we will call bias regions, for each amplifier. The quadformat requires the bias regions to be attached to the CCD regions such that a single rectangular region contains both.
Generally the rectangular regions are of equal size in order to sequence the amplifiers simultaneously. However, it is possible for the regions to be unequal in cases of subregion readouts with certain CCD controllers. The figure below illustrates a "dual" and "quad" readout with equal size regions.
+-----+-+-+-----+ +-----+-+-+-----+ +----------+-+
| D !B|B! D | | D !B|B! D | | D !B|
| 3 !3|4! 4 | | 1 !1|2! 2 | | 2 !2|
| ! | ! | | ! | ! | | ! |
+-----+-+-+-----+ | ! | ! | +----------+-+
| D !B|B! D | | ! | ! | | D !B|
| 1 !1|2! 2 | | ! | ! | | 1 !1|
| ! | ! | | ! | ! | | ! |
+-----+-+-+-----+ +-----+-+-+-----+ +----------+-+
The areas labeled D are the data sections and those labeled B are the bias sections. The data and biases are match by the amplifier labels which are 1-4 in these examples. The combination of the data and bias sections are called the amplifier sections.
The regions are identified in the header by various keywords. There is a header translation facility which allows for alternative keyword names. Below we describe the default keyword names in the absence of a translation. The number of regions and the amplifier labels are described by the string keyword AMPLIST. The value is a string of space separated amplifier labels. For the above four amplifier example it would be
AMPLIST = '1 2 3 4'
For CTIO data the labels are '11 12 21 22'. Note that the labels are appended to rootnames so they should be relatively short.
The amplifier labels are appended to various root names. The important ones define "section" keywords. The values are image sections that describe regions in an raster such as the image or the CCD. The format of a section follows the standard IRAF notation "[c1:c2,l1:l2]" where c1 and c2 are inclusive column endpoints and l1 and l2 are inclusive line endpoints.
The various sections are defined below. The labels again show the default untranslated keyword roots.
- ASEC
- The section of the image containing the amplifier readout. This is the combination of the data and bias regions as shown in the figures.
- DSEC
- The section of the image containing the actual CCD data exclusive of bias data. In the figures these are the D regions.
- BSEC
- The section of the image containing the bias data. In the figures these are the B regions.
- TSEC
- The second of the image containing the useful CCD data. This defines a "trimming" area and lies within the data section. It may also be the same as the data region. During trimming the final image will only include the regions in the trim sections. Note that it generally does not make sense to trim between amplifier regions but does make sense to trim regions at the edges of the CCD.
- CSEC
- The section of the CCD corresponding to the data section in the image. The CCD is considered an ideal raster (without bias regions) and a section corresponds to the pixels in the CCD. The CCD section must be the same size as the data section. It is the CCD sections that define how the amplifiers will be pieced together to form a single image after trimming the bias region.
There may be other keyword root names for things such as gains which have the amplifier labels appended. However, none of these are used by the current software. Example image headers are given in the EXAMPLES section.
There is a limitation in the current software that the regions be recorded without horizontal or vertical flips. In other words, where amplifiers from opposite corners are used some of them must be flipped by the data acquisition system before recording then in this quadformat.
Examples
1. The following is an example of a full 2048x2048 CCD readout with four amplifiers at CTIO.
qu> imhad quad0020
quad0020[2196,2048][ushort]: IC 1257 5290 180s
No bad pixels, min=435., max=61973.
Line storage mode, physdim [2304,2048], length of user area 3079 s.u.
Created Thu 08:35:57 23-Aug-2001, Last modified Thu 08:35:57 23-Aug-2001
Pixel file "HDR$pixels/quad0020.pix" [ok]
'KPNO-IRAF' /
'06-07-99' /
IRAF-MAX= 6.197300E4 / DATA MAX
IRAF-MIN= 4.350000E2 / DATA MIN
IRAF-BPX= 16 / DATA BITS/PIXEL
IRAFTYPE= 'USHORT ' / PIXEL TYPE
OPICNUM = 123 / Original picture number
HDR_REV = '2.000 13Feb96 (add mode and group to hdrs)' /
IMAGETYP= 'OBJECT ' / Type of picture (object, dark, etc.)
DETECTOR= 'Site2K_6' / Detector (CCD type, photon counter, etc.)
PREFLASH= 0.000000 / Preflash time in secs
CCDSUM = '1 1 ' / On chip summation (X,Y)
DATE-OBS= '07/07/99' / Date (dd/mm/yy) of observation
UTSHUT = '01:14:40.0' / UT of shutter open
UT = ' 1:14:41.50' / UT of TCS coords
OBSERVAT= 'CTIO ' / Origin of data
TELESCOP= 'CTIO 1.5 meter telescope' / Specific system
NAMPSYX = '2 2 ' / Num amps in y & x (eg. '2 2'=quad)
AMPLIST = '11 21 12 22' / Readout order in y,x
ASEC11 = '[1:1098,1:1024]' / Section read with Amp11
CSEC11 = '[1:1034,1:1024]' / Section in full CCD for DSEC11
DSEC11 = '[1:1034,1:1024]' / Image area in raw frame for Amp11
TSEC11 = '[11:1034,1:1024]' / Trim section definition for Amp11
BSEC11 = '[1045:1098,1:1024]' / Bias section definition for Amp11
BSEC12 = '[1099:1152,1:1024]' / Bias section definition for Amp12
ASEC12 = '[1099:2196,1:1024]' / Section read with Amp12
CSEC12 = '[1035:2068,1:1024]' / Section in full CCD for DSEC12
DSEC12 = '[1163:2196,1:1024]' / Image area in raw frame for Amp12
TSEC12 = '[1163:2186,1:1024]' / Trim section definition for Amp12
ASEC21 = '[1:1098,1025:2048]' / Section read with Amp21
CSEC21 = '[1:1034,1025:2048]' / Section in full CCD for DSEC21
DSEC21 = '[1:1034,1025:2048]' / Image area in raw frame for Amp21
TSEC21 = '[11:1034,1025:2048]' / Trim section definition for Amp21
BSEC21 = '[1045:1098,1025:2048]' / Bias section definition for Amp21
BSEC22 = '[1099:1152,1025:2048]' / Bias section definition for Amp22
ASEC22 = '[1099:2196,1025:2048]' / Section read with Amp22
CSEC22 = '[1035:2068,1025:2048]' / Section in full CCD for DSEC22
DSEC22 = '[1163:2196,1025:2048]' / Image area in raw frame for Amp22
TSEC22 = '[1163:2186,1025:2048]' / Trim section definition for Amp22
WAVEFILE= 'Obs Tue Jul 6 20:11:59 1999' /
NOTE = 'WARNING: Lower amps reaching full well before ADCs saturate' /
WAVEMODE= 'MPP OverlapXmit EarlyReset' / Waveform mode switches on
GTRON22 = 4.100 / (e-) predicted read noise, upper right
GTRON21 = 3.900 / (e-) predicted read noise, upper left
GTRON12 = 4.200 / (e-) predicted read noise, lower right
GTRON11 = 4.200 / (e-) predicted read noise, lower left
GTGAIN22= 2.800 / (e-/ADU), predicted gain, upper right
GTGAIN21= 3.100 / (e-/ADU) predicted gain, upper left
GTGAIN12= 2.900 / (e-/ADU) predicted gain, lower right
GTGAIN11= 3.200 / (e-/ADU) predicted gain, lower left
GTINDEX = 2 / Gain selection (index into Gain Table)
PIXELT = 29520 / (ns) unbinned pixel read time
DCS_TIME= 7000 / (ns) Double Correlated Sample time
RA = '17:27:10.82' / right ascension (telescope)
DEC = '-7:06:35.40' / declination (telescope)
EPOCH = 2000.0 / epoch of RA & DEC
ZD = 35.9 / zenith distance (degrees)
HA = '-01:57:23.7' / hour angle (H:M:S)
ST = '15:29:46.00' / sidereal time
AIRMASS = 1.234 / airmass
EXPTIME = 180.000 / Exposure time in secs
DARKTIME= 181.309 / Total elapsed time in secs
OBSERVER= 'Jacoby' / Observers
PROPID = '92' / Proposal Id
COMMENT Globular PNe
TELID = 'ct60' / CTIO 1.5-m Telescope
ARCONVER= '17Oct97ver7_22' / Arcon software version
COMMENT INSTRUMENT PARAMETERS
INSTRUME= 'cfccd' / cassegrain direct imager
FILTER1 = 'dia' / Filter in wheel one
FNAME1 = 'diaphragm' / Full name of filter in wheel1
FILTER2 = 'ocon' / Filter in wheel two
FNAME2 = 'O cont' / Full name of filter in wheel2
FILTERS = 'dia ocon' / Filter positions
TELFOCUS= 57550 / Telescope focus
XPIXSIZE= 0.432 / Pixel size in X (arcsec/pix)
YPIXSIZE= 0.432 / Pixel size in Y (arcsec/pix)
RECID = 'ct60.990707.011817' / NOAO Archive record ID
2. The following is a more complex readout of a region where the full 2Kx2K CCD is not readout and where even the regions are not the same size.
qu> imhead quad0013
quad0013[1686,1538][ushort]: R sky flat 7s
No bad pixels, min=393., max=65535.
Line storage mode, physdim [1792,1538], length of user area 3079 s.u.
Created Thu 08:34:00 23-Aug-2001, Last modified Thu 08:34:00 23-Aug-2001
Pixel file "HDR$pixels/quad0013.pix" [ok]
'KPNO-IRAF' /
'06-07-99' /
IRAF-MAX= 6.553500E4 / DATA MAX
IRAF-MIN= 3.930000E2 / DATA MIN
IRAF-BPX= 16 / DATA BITS/PIXEL
IRAFTYPE= 'USHORT ' / PIXEL TYPE
OPICNUM = 15 / Original picture number
HDR_REV = '2.000 13Feb96 (add mode and group to hdrs)' /
IMAGETYP= 'SKY FLAT' / Type of picture (object, dark, etc.)
DETECTOR= 'Site2K_6' / Detector (CCD type, photon counter, etc.)
PREFLASH= 0.000000 / Preflash time in secs
CCDSUM = '1 1 ' / On chip summation (X,Y)
DATE-OBS= '06/07/99' / Date (dd/mm/yy) of observation
UTSHUT = '22:25:22.0' / UT of shutter open
UT = '22:25:34.00' / UT of TCS coords
OBSERVAT= 'CTIO ' / Origin of data
TELESCOP= 'CTIO 1.5 meter telescope' / Specific system
NAMPSYX = '2 2 ' / Num amps in y & x (eg. '2 2'=quad)
AMPLIST = '11 21 12 22' / Readout order in y,x
ASEC11 = '[1:843,1:769]' / Section read with Amp11
CSEC11 = '[256:1034,256:1024]' / Section in full CCD for DSEC11
DSEC11 = '[1:779,1:769]' / Image area in raw frame for Amp11
TSEC11 = '[11:779,1:769]' / Trim section definition for Amp11
BSEC11 = '[790:843,1:769]' / Bias section definition for Amp11
BSEC12 = '[844:897,1:769]' / Bias section definition for Amp12
ASEC12 = '[844:1686,1:769]' / Section read with Amp12
CSEC12 = '[1035:1813,256:1024]' / Section in full CCD for DSEC12
DSEC12 = '[908:1686,1:769]' / Image area in raw frame for Amp12
TSEC12 = '[908:1418,1:769]' / Trim section definition for Amp12
ASEC21 = '[1:843,770:1538]' / Section read with Amp21
CSEC21 = '[256:1034,1025:1793]' / Section in full CCD for DSEC21
DSEC21 = '[1:779,770:1538]' / Image area in raw frame for Amp21
TSEC21 = '[11:779,770:1280]' / Trim section definition for Amp21
BSEC21 = '[790:843,770:1538]' / Bias section definition for Amp21
BSEC22 = '[844:897,770:1538]' / Bias section definition for Amp22
ASEC22 = '[844:1686,770:1538]' / Section read with Amp22
CSEC22 = '[1035:1813,1025:1793]' / Section in full CCD for DSEC22
DSEC22 = '[908:1686,770:1538]' / Image area in raw frame for Amp22
TSEC22 = '[908:1418,770:1280]' / Trim section definition for Amp22
WAVEFILE= 'Obs Tue Jul 6 18:07:56 1999' /
NOTE = 'WARNING: Lower amps reaching full well before ADCs saturate' /
WAVEMODE= 'MPP OverlapXmit EarlyReset' / Waveform mode switches on
GTRON22 = 4.100 / (e-) predicted read noise, upper right
GTRON21 = 3.900 / (e-) predicted read noise, upper left
GTRON12 = 4.200 / (e-) predicted read noise, lower right
GTRON11 = 4.200 / (e-) predicted read noise, lower left
GTGAIN22= 2.800 / (e-/ADU), predicted gain, upper right
GTGAIN21= 3.100 / (e-/ADU) predicted gain, upper left
GTGAIN12= 2.900 / (e-/ADU) predicted gain, lower right
GTGAIN11= 3.200 / (e-/ADU) predicted gain, lower left
GTINDEX = 2 / Gain selection (index into Gain Table)
PIXELT = 29520 / (ns) unbinned pixel read time
DCS_TIME= 7000 / (ns) Double Correlated Sample time
RA = '14:53:52.67' / right ascension (telescope)
DEC = '-19:20:10.70' / declination (telescope)
EPOCH = 2000.0 / epoch of RA & DEC
ZD = 32.1 / zenith distance (degrees)
HA = '-02:13:40.3' / hour angle (H:M:S)
ST = '12:40:10.80' / sidereal time
AIRMASS = 1.180 / airmass
EXPTIME = 7.000 / Exposure time in secs
DARKTIME= 8.239 / Total elapsed time in secs
OBSERVER= 'Jacoby' / Observers
PROPID = '92' / Proposal Id
COMMENT
TELID = 'ct60' / CTIO 1.5-m Telescope
ARCONVER= '17Oct97ver7_22' / Arcon software version
COMMENT INSTRUMENT PARAMETERS
INSTRUME= 'cfccd' / cassegrain direct imager
FILTER1 = 'dia' / Filter in wheel one
FNAME1 = 'diaphragm' / Full name of filter in wheel1
FILTER2 = 'r' / Filter in wheel two
FNAME2 = 'R' / Full name of filter in wheel2
FILTERS = 'dia r' / Filter positions
TELFOCUS= 0 / Telescope focus
XPIXSIZE= 0.432 / Pixel size in X (arcsec/pix)
YPIXSIZE= 0.432 / Pixel size in Y (arcsec/pix)
RECID = 'ct60.990706.222551' / NOAO Archive record ID
3. The following is for the raw image of example 2 after it has been processed by CCDPROC. Note that the various bias, trim, and CCD sections are removed. The AMPLIST and ASEC keywords remain and may be used to split or evaluate the individual amplifier regions with tasks such as QUADSECTIONS, QUADSPLIT, and QSTATISTICS.
qu> imhead quad0013
quad0013[1280,1280][real]: R sky flat 7s
No bad pixels, min=unknown, max=unknown
Line storage mode, physdim [1280,1280], length of user area 2795 s.u.
Created Fri 13:29:40 24-Aug-2001, Last modified Fri 13:29:40 24-Aug-2001
Pixel file "HDR$pixels/quad0013.pix" [ok]
'KPNO-IRAF' /
'06-07-99' /
New copy of quad0013
IRAF-MAX= 6.553500E4 / DATA MAX
IRAF-MIN= 3.930000E2 / DATA MIN
IRAF-BPX= 16 / DATA BITS/PIXEL
IRAFTYPE= 'USHORT ' / PIXEL TYPE
OPICNUM = 15 / Original picture number
HDR_REV = '2.000 13Feb96 (add mode and group to hdrs)' /
IMAGETYP= 'SKY FLAT' / Type of picture (object, dark, etc.)
DETECTOR= 'Site2K_6' / Detector (CCD type, photon counter, etc.)
PREFLASH= 0.000000 / Preflash time in secs
CCDSUM = '1 1 ' / On chip summation (X,Y)
DATE-OBS= '06/07/99' / Date (dd/mm/yy) of observation
UTSHUT = '22:25:22.0' / UT of shutter open
UT = '22:25:34.00' / UT of TCS coords
OBSERVAT= 'CTIO ' / Origin of data
TELESCOP= 'CTIO 1.5 meter telescope' / Specific system
NAMPSYX = '2 2 ' / Num amps in y & x (eg. '2 2'=quad)
AMPLIST = '11 21 12 22' / Readout order in y,x
ASEC11 = '[1:769,1:769]' / Section read with Amp11
ASEC12 = '[770:1280,1:769]' / Section read with Amp12
ASEC21 = '[1:769,770:1280]' / Section read with Amp21
ASEC22 = '[770:1280,770:1280]' / Section read with Amp22
WAVEFILE= 'Obs Tue Jul 6 18:07:56 1999' /
NOTE = 'WARNING: Lower amps reaching full well before ADCs saturate' /
WAVEMODE= 'MPP OverlapXmit EarlyReset' / Waveform mode switches on
GTRON22 = 4.100 / (e-) predicted read noise, upper right
GTRON21 = 3.900 / (e-) predicted read noise, upper left
GTRON12 = 4.200 / (e-) predicted read noise, lower right
GTRON11 = 4.200 / (e-) predicted read noise, lower left
GTGAIN22= 2.800 / (e-/ADU), predicted gain, upper right
GTGAIN21= 3.100 / (e-/ADU) predicted gain, upper left
GTGAIN12= 2.900 / (e-/ADU) predicted gain, lower right
GTGAIN11= 3.200 / (e-/ADU) predicted gain, lower left
GTINDEX = 2 / Gain selection (index into Gain Table)
PIXELT = 29520 / (ns) unbinned pixel read time
DCS_TIME= 7000 / (ns) Double Correlated Sample time
RA = '14:53:52.67' / right ascension (telescope)
DEC = '-19:20:10.70' / declination (telescope)
EPOCH = 2000.0 / epoch of RA & DEC
ZD = 32.1 / zenith distance (degrees)
HA = '-02:13:40.3' / hour angle (H:M:S)
ST = '12:40:10.80' / sidereal time
AIRMASS = 1.180 / airmass
EXPTIME = 7.000 / Exposure time in secs
DARKTIME= 8.239 / Total elapsed time in secs
OBSERVER= 'Jacoby' / Observers
PROPID = '92' / Proposal Id
COMMENT
TELID = 'ct60' / CTIO 1.5-m Telescope
ARCONVER= '17Oct97ver7_22' / Arcon software version
COMMENT INSTRUMENT PARAMETERS
INSTRUME= 'cfccd' / cassegrain direct imager
FILTER1 = 'dia' / Filter in wheel one
FNAME1 = 'diaphragm' / Full name of filter in wheel1
FILTER2 = 'r' / Filter in wheel two
FNAME2 = 'R' / Full name of filter in wheel2
FILTERS = 'dia r' / Filter positions
TELFOCUS= 0 / Telescope focus
XPIXSIZE= 0.432 / Pixel size in X (arcsec/pix)
YPIXSIZE= 0.432 / Pixel size in Y (arcsec/pix)
RECID = 'ct60.990706.222551' / NOAO Archive record ID
TRIM = 'Aug 24 13:29 Trim multiple overscan sections'
OVERSCAN= 'Aug 24 13:29 Overscan is [790:843,1:769] with mean=714.3438'
OVRSCN2 = 'Aug 24 13:29 Overscan is [790:843,770:1538] with mean=554.01'
OVRSCN3 = 'Aug 24 13:29 Overscan is [844:897,1:769] with mean=519.7755'
OVRSCN4 = 'Aug 24 13:29 Overscan is [844:897,770:1538] with mean=531.69'
CCDSEC = '[266:1545,256:1535]'
CCDMEAN = 9727.605
CCDMEANT= 683126983
CCDPROC = 'Aug 24 13:29 CCD processing done'