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load'media/platimg' NB. image reader
load'viewmat plot'
NB. gray scale viewer
viewgray=: (16b010101*i.256)&viewmat
glwh=: 3 : 'wd''pmovex '',(+0 0,y-glqwh_jgl2_@$@#)&.".wd''qformx'''
viewwh=: glwh@|.@$ [ viewgray
$M=. 16bff (17 b.) readimg jpath'~temp\input.jpg'
1200 1600
viewwh M
$R=: |:_5(+/%#)\|: _5(+/%#)\ M NB. reduced large image
240 320
viewwh R
'surface;mesh 0' plot R NB. notice features below smooth light
S=: |: _10(>./)\|: _10(>./)\ M NB. so apply max filter to remove features
Z=: 2#"1]2#S NB. restore size
W=: |:8 (+/%#)\|:8 (+/%#)\ Z NB. smooth with moving average
viewwh W
viewwh N=: (($W){.R) - W NB. remove shadow
Polynomial surface subtraction
IGOR Pro from WaveMetrics suggests such background removal
- manually selecting point using ROI (region of interest) tool
- interpolate polynomial fit into point
- subtract polynomial
Background could additive (for subtraction removal) or multiplicative (for division).
Removing Averages
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Procedure for Electron Backscatter Diffraction (EBSD) of Oxford Instruments suggests that "the background can be measured by scanning the beam over many grains in the sample to average out the diffraction information. The background can be removed by subtraction from, or division into, the original pattern".
ImageJ Plugins
A number of ImageJ pluggins provide background correction.
Base system itself has built-in support for subtracting background.