Gaussian 1-D Convolution

In an attempt to remove some of the unexpected behavior in stacking and differencing, a new mode was added to the pmSubtraction code. This mode defines a new kernel type PM_SUBTRACTION_KERNEL_SIMPLE which breaks out from the current Alard-Lupton PSF matching code into work-alike replacement.

Mathematically, instead of attempting to do the PSF matching with a sum of the product of Gaussians and polynomials, this SIMPLE kernel examines only the measured FWHM values for the two PSFs. From these values, a Gaussian kernel is constructed with sigma_kern² = (FWHM_large² - FWHM_small²)/(2 sqrt(2 log 2))². The smaller PSF image is then convolved by this kernel and the results returned.

Below are a series of comparison images from tests with real GPC1 data. The left panel shows the standard pmSubtraction kernels, and the right shows the new SIMPLE kernel.

Convolved stack:

Unconvolved stack:

Warp-warp diff:

Real object zoom in diff:

After processing the SAS stacks and static sky with the 1-D Gaussian convolution, we can compare the timing for these stages between the two PSF matching codes using the dtime values listed in the database. For all subsequent plots, the x-axis shows the default time with the pmSubtraction kernels (SAS.20130620), and the y-axis shows the ratio of simple/default (SAS.20130703/SAS.20130620).