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Changes between Version 11 and Version 12 of Kron_measurements_investigation


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Timestamp:
May 26, 2012, 2:09:55 PM (14 years ago)
Author:
bills
Comment:

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  • Kron_measurements_investigation

    v11 v12  
    1 == PSPHOT Kron Measurements investigation ==
     1= PSPHOT Kron Measurements Investigation =
    22
    33This page describes some investigations comparing the Kron radius and magnitudes measured by psphot
    4 
    5 Outline (most sections TODO)
    6  * Overview of the Issue
    7  * Data Sample
    8  * Recipe Choices
    9    * Default: Smooth, apply window function, apply weight function
    10    * No Window
    11    * No weight
    12    * No Window no weight, no smooth
    13    * No Window no weight, no smooth
    14  * Results
    154
    165== Overview ==
    … …  
    198See plot at http://ps1sc.ifa.hawaii.edu/PS1wiki/index.php/KP12videocon_page#Kron_radii_-_possible_improvement
    209
    21 Using a set of 40 simulated images provided by Peter we have done many experiments with psphot to invesigate
     10Using a set of 40 simulated images provided by Peter we have done many experiments with psphot to investigate
    2211the accuracy of the kron measurements. We reported April 30 at the DRAVG
    23 meeting that results closer to SEXtractor can be achieved with a prototype version of psphot which
    24 smooths the input image with a 1.7 pixel gaussian prior to measuring the kron radius and flux.
     12meeting that results closer to SEXtractor can be achieved with a prototype version of psphot that
     13smooths the input image with a 1.7 pixel Gaussian prior to measuring the kron radius and flux.
    2514http://ps1sc.ifa.hawaii.edu/PS1wiki/index.php/DRAVG_telecon#Kron_radii_improvements
    2615
    27 We have more carefully implemented the smoothing function and the code is now included in the ipp-trunk.
     16We have more carefully implemented the smoothing function and the code is now included in the ipp-trunk. There are several recipe values that now may be used to control the psphot kron measurements. Current defaault values are listed.
    2817
    29 There are several recipe values that now may be used to control the psphot kron measurements
     18* PSPHOT_APPLY_WEIGHT T apply gaussian weight of sigma == windowRadius
     19* PSPHOT_APPLY_WINDOW T apply window function to downweight subtracted sources
     20* PSPHOT_KRON_SMOOTH  F when true smooth the input image before measuring the kron radius
     21* PSPHOT_KRON_SIGMA   1.7 smoothing parameter
     22* PSPHOT KRON_NSIGMA  2 smoothing parameter
    3023
    31 
    32 
    33 
     24Upon reviewing the following results the differences between applying the weighting and window functions are not significant. We suggest turning them off.
     25The smoothing yields kron radii closer to SExtractor with these simulated images. We need to investigate the performance impact on single frame psphot
     26before deciding to turn it on.
    3427
    3528== Results ==
    … …  
    144137Considering sources with SE kron radii above 10  the smallest stdev is also with the default recipe.
    145138The window function appears to have has little effect on the statistics. The biggest improvement is provided
    146 by the smoothing. Withoug smoothing the psphot KR is systematically low.
     139by the smoothing. Without smoothing the psphot KR is systematically low.
    147140
    148141---------------------------------------------------------------------------------------------------------------