Looking again at your problem my experiences with both statistics
and images say that the *median* would be a better average than
the *arithmeticMean*. So you could try and compare both averages
(more exactly: location parameters of your WxH-color-distribution).
local t="temp"
-- hL,vL is the topleft of the pixel-rect on your screen
-- the width of the pixel-rect is w. W is an integer >= 1.
-- the height of the pixel-rect is h. H is an integer >= 1.
-- tp is the average method "median" or (default:) "arithmeticMean"
-- average is taken from the pixel-colors of rect (hL,vL,hL+w,vL+h)
--
function averageColor w,h,hL,vL,tp
export snapshot from rect (hL,vL,hL+w,vL+h) to img t as PNG
put the imagedata of img t into iData
put the alphadata of img t into aData
repeat with i=1 to w*h
put byteToNum(byte 4*i-2 of iData) into redA[i]
put byteToNum(byte 4*i-1 of iData) into greenA[i]
put byteToNum(byte 4*i of iData) into blueA[i]
put byteToNum(byte i of aData) into alphaA[i]
end repeat
if tp is "median" then
return trunc(median(redA)),trunc(median(greenA)), \
trunc(median(blueA)),trunc(median(alphaA))
else
return trunc(avg(redA)),trunc(avg(greenA)), \
trunc(avg(blueA)),trunc(avg(alphaA))
end if
end averageColor
-- usage example:
on mouseUp
lock screen; lock messages
put 5 into w0; put 5 into h0
put -w0+the left of this stack into sL
put -h0+the top of this stack into sT -- = without window bar
####
if there is no img "temp" then create invisible img t
if there is no field t then
create fld t
set rect of fld t to (0,0,128,23)
set botleft of fld t to the botright of me
end if
if there is no grc t then
create grc t
set opaque of grc t to true
set rect of grc t to (0,0,23,23)
set botright of grc t to the botleft of me
end if
####
put averageColor(w0,h0,sL,sT,"median") into x --> returns r,g,b,alpha
#### use x, for example:
set backColor of grc t to item 1 to 3 of x
--set blendlevel of grc t to round(100*(1-(item 4 of x)/255)) -- if wanted
put x into fld t
unlock screen; unlock messages
end mouseUp
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