6.4 The QualityFITS input and output products

QualityFITS is a Terapix quality assessment tool for FITS images. During CFHTLS T0007 production, it is used to assess whether individual CFHT input images and the CFHTLS output stacks meet the survey specifications. QualityFITS also produces the input weight-map images as well as the input .ldac catalogues.

The quality assessments are done from a visual inspection of QualityFITS outputs and from a series of statistics, tables and plots. An overview and a quick-look image quality assessments can be made using the QualityFITS web page. This “ID-card” for each image is produced automatically and is used to grade all images through the Youpi user interface27 .

The information returned by QualityFITS depends on the type of images (Multi-extension fits (MEF) or single extension FITS, the type of detectors (single CCD, mosaic of CCDs) and the origin of images. Depending on the steps of the processing (evaluation of input images or of final stacks), they are referenced as QualityFITS-in (or QFITS-in) or QualityFITS-out (or QFITS-out) products.

As a general rule any CFHT images entering or leaving the Terapix center is passes through QualityFITS-in or QualityFITS-out processing steps. 7042 CFHTLS input images and the 2276 T0007 output images were evaluated using this tool.

The QualityFITS data products are images, tables and plots:

The QualityFITS output files are all public. The QualityFITS QA pages are available from the synoptic table. The T0007 synoptic table is a convenient way to have a quick look at the images.

Figure 48: QFITS-out page of the W4 CFHTLS_W_i_222054+002300 stack. The top table summarises the images origin and the nature of the stack. The next images show, from top left to bottom right: binned images of the stack, its weight-map, and the sky background; the PSF over the MegaCam field. The plots at the bottom show the galaxy counts (left) derived from the .ldaccatalogue. The galaxies are extracted from a blind selection of the sources shown on the right rh -mag plot (red points). The red line on the galaxy count plot is the expectation.

Figure 49: QFITS-out page of the same field (cont’d). The clickable plots show, from top left to bottom right, the stellar-counts (left) derived from a blind selection of red sources shown on the right rh - magnitude plot. The red line is the predictions of the Bahcall-Soneira model. The plot on the middle panel shows the amplitude ((a2 -b2)(a2 + b2) = length of lines) and the orientation (= orientation of lines) of the stellar ellipticity vectors over the MegaCam field. The seelcted sources are the red points shown on the right rh - magnitude plot. The plots at the bottom are the 2-dimensional (left) and 1-dimensional astrometric errors of sources with respect to the 2MASS catalogue. They are produced by running SCAMP in a simple diagnostic mode (-match n -solve_astrom n -solve_photom n).

Figure 50: QFITS-out page of the same field (cont’d). The clickable images are full resolution sub-images of the bottom left corners of the stack. The table below summarises some basic information of the stack: sky background, mean seeing, number of sources.