Fred's ImageMagick Scripts



 

 

PLM


Generates a piece-wise linear mapping grayscale look up table and applies it to an image

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last modified: August 20, 2008



USAGE: plm [-s xscale,yscale] [-g] "x1,y1 x2,y2 ..." infile outfile
USAGE: plm [-s xscale,yscale] [-g] -f point_file infile outfile
USAGE: plm [-h or -help]

"x1,y1 x2,y2 ..." ....... break point values of piece-wise linear transformation
......................... enclosed in quotes; minimum of one (x,y) break point pair;
......................... x corresponds to the graylevel in the input image;
......................... y corresponds to the graylevel in the outut image;
......................... x,y non-negative floats enclosed in quotes;
......................... list must be specified just prior to lutfile
-f ... point_file ....... text file containing list of break points;
......................... one x,y pair per line
-s ... xscale,yscale .... range of values for x,y breakpoint pairs from 0 to xscale,yscale;
......................... positive integers; default=100,100
-g ...................... enables the creation of a graph of the piece-wise linear
......................... transformation, which is then displayed automatically.
......................... There is a default setting below that can be changed
......................... to enable this to be save to a file named outfile_graph.gif

PURPOSE: To generate a piece-wise linear mapping grayscale look up table and applies it to an image (infile) to generate a new image (outfile).

DESCRIPTION: PLM takes the supplied break point pairs and generates a one dimensional piece-wise linear grayscale look up table image that is used to change grayscale values in the channels of the input image. From 1 to 40 point pairs can be supplied either as arguments or in a text file with one pair per line supplied. The x value is the position in the look up table which is associated with the grayscale value of the desired channels of the input image and the y value is the associated grayscale value for the corresponding channels in the resulting output image.

ARGUMENTS:

"x1,y1 x2,y2" ... List of x,y break-points for the piece-wise linear transformation. The x,y values are non-negative break-point pairs for the piece-wise linear transformation. There is a minimum one point pair that must be supplied. The x and y values are associated with the input and output grayscale values of the look up table, where x,y values can range from 0 to xscale,yscale. xscale determines the length of the 1D lookup table (length=xscale + 1); that is, the range of x (input) values and yscale determines the range of y (output) values. Both xscale and yscale must be positive integers and their defaults are 100. If the first pair is not 0,0 or the last pair is not xscale,yscale then those points will be added automatically to the list of point pairs. IMPORTANT: the list of break-point pairs must be specified just prior to infile outfile.

-f point_file ... point-file is a text file containing the list of break points, one x,y pair per line.

-s xscale,yscale ... xscale,yscale is the range of values for the x,y breakpoint pairs which go from 0 to xscale,yscale; positive integers. The default is 100,100. Larger values for xscale and yscale can be used for more accuracy. For example with xscale=yscale=100, x and y values are specified between 0 and 100 and the length of the output image is 101 pixels. For xscale=yscale=255, x and y values are specified # between 0 and 255 and the length of the output image is 256. Equal values for xscale and yscale are not required.

-g ... enables the creation of a graph of the piece-wise linear transformation, which is then displayed automatically. There is a default setting below that can be changed to enable this to be save to a file named outfile_graph.gif. The graph will be scaled to size 100x100. IMPORTANT: To end the script, close/quit the graph image.

CAVEAT: No guarantee that this script will work on all platforms, nor that trapping of inconsistent parameters is complete and foolproof. Use At Your Own Risk.


EXAMPLES


Original Color Image

Original Grayscale Image



Various Piece-wise Linear (Internally Generated) LUTs Applied To Color Image

arguments:
0,0 100,100
no change

arguments:
0,0 33,0 66,100 100,100
increase contrast

arguments:
0,0 44,0 45,100 55,100 56,0 100,0
color slice



Various Piece-wise Linear (Internally Generated) LUTs Applied To Grayscale Image

arguments:
0,0 100,100
no change

arguments:
0,0 33,0 66,100 100,100
increase contrast

arguments:
0,0 44,0 45,100 55,100 56,0 100,0
grayscale slice



Invert Values

Input

PLM arguments:
"0,100 100,0"

PLM Graph

IM arguments:
-negate

IM Command Graph



Threshold

Input

PLM arguments:
"0,0 50,0 50,100 100,100"

PLM Graph

IM arguments:
-channel RGB -threshold 50%

IM Command Graph



Black Threshold

Input

PLM arguments:
"0,0 50,0 50,50 100,100"

PLM Graph

IM arguments:
-separate -black-threshold 50% -combine

IM Command Graph



White Threshold

Input

PLM arguments:
"0,0 50,50 50,100 100,100"

PLM Graph

IM arguments:
-separate -white-threshold 50% -combine

IM Command Graph



Increase Contrast

Input

PLM arguments:
"25,0 75,100" or
"0,0 25,0 75,100 100,100"

PLM Graph

IM arguments:
-level 25% or
-level 25,75%

IM Command Graph



Decrease Contrast

Input

PLM arguments:
"0,25 100,75"

PLM Graph

IM arguments:
+level 25% or
+level 25,75%

IM Command Graph



Constant Gray

Input

PLM arguments:
"0,50 100,50"

PLM Graph

IM arguments:
+level 50,50%

IM Command Graph



Clip Low

Input

PLM arguments:
"0,25 25,25 100,100"

PLM Graph

IM arguments:
-level 25%,100% +level 25%,100%

IM Command Graph



Clip High

Input

PLM arguments:
"0,0 75,75 100,75"

PLM Graph

IM arguments:
-level 0,75% +level 0,75%

IM Command Graph



Clip Low And High

Input

PLM arguments:
"0,25 25,25 75,75 100,75"

PLM Graph

IM arguments:
-level 25% +level 25% or
-level 25,75% +level 25,75%

IM Command Graph



Crude One Point Gamma Approximation

Input

PLM arguments:
"8,29" or
"0,0 8,29 100,100"

PLM Graph

IM arguments:
-gamma 2

IM Command Graph



Crude Two Point Sigmoidal-Contrast Approximation

Input

PLM arguments:
"30,10 70,90" or
"0,0 30,10 70,90 100,100"

PLM Graph

IM arguments:
-sigmoidal-contrast 10,50%

IM Command Graph



Ramp-Horizontal-Ramp

Input

PLM arguments:
"0,0 25,50 75,50 100,100"

PLM Graph

IM arguments:
???

IM Command Graph

   


Ramp-Vertical-Ramp

Input

PLM arguments:
"0,0 50,25 50,75 100,100"

PLM Graph

IM arguments:
???

IM Command Graph

   


Truncated Triangle

Input

PLM arguments:
"0,0 40,0 40,100 60,100 60,0 100,0"

PLM Graph

IM arguments:
-solarize 50% -level 0,40%

IM Command Graph



Slice

Input

PLM arguments:
"0,0 40,0 40,100 60,100 60,0 100,0"

PLM Graph

IM arguments:
-solarize 50% -channel RGB -threshold 40%

IM Command Graph



Sawtooth Blinds

Input

PLM arguments:
"0,0 25,100 25,0 50,100 50,0 75,100 75,0 100,100"

PLM Graph

IM arguments:
+clone +clone +clone -background black \
-compose add -flatten \
(close but not quite the same)

IM Command Graph



What the script does is as follows:

  • Creates a black background image
  • Draws a filled white polygon using specified break points
    and additional points needed to make a closed polygon
  • Removes the first row of the image
  • Do a box average of each column in the image to create the lut
  • Apply the lut to the image

This is equivalent to the following IM commands for the
break points: 0,20 100,80 which decrease contrast.

  • convert $infile \
    \( -size 101x101 xc:black -fill white \
    -draw "polygon 0,0 0,20 100,80 100,0" \
    -crop 101x100+0+1 +repage \
    -scale 101x1! \) \
    -clut $outfile