snibgo's ImageMagick pages

Adaptive contour blur and sharpen

The effect is along, or across, edges.

The script on Adaptive blur and sharpen applies a Gaussian (circular, 2D) blur/sharpen. This page develops that idea, applying a linear blur/sharpen that is either parallel or perpendicular to contours. (A contour is an imaginary line that joins pixels of equal intensity.) The effect is anisotropic, meaning the effect is directional.

Although a linear blur is conceptually simpler than a 2D blur, it offers more possibilities.

Sample input

We will demonstrate on the usual image:

set SRC=toes.png
 toes.pngjpg

The script

The script adapContBlrShp.bat blurs or sharpens an image, with the greatest effect either where there is most detail (the edges) or where there is least detail (non-edges).

Parameter Description
%1 Input image (mandatory parameter)
%2 Output image
%3 One of:
  • E blur at the edges (where the mask is light)
  • N blur at the non-edges (where the mask is dark)
Default: N
%4 Edge detector sigma
Default: 10
%5 Blur sigma
Default: half of %4
%6 Blend percentage
  • 0 for no effect
  • >0 for blur
  • <0 for sharpen
Default: 100
%7 Colorspace for operation
%8 Blur direction, one of:
  • Parallel to contours
  • Perpendicular to contours
Default: Parallel

The input is mandatory. All other parameters are optional. As usual, a dot "." may be used as a placeholder.

The script adapContBlrShp.bat blurs an image using a mask that is white where there is most detail, and black where there is least detail. By default the mask is negated, so the blur is greatest where there is least detail. The blurred result is blended with the input at a certain percentage. The default percentage is 100 so the result is the blur. Alternative percentages include zero so there is no effect, and -100 so the effect is a sharpening. Other values can be used, eg 50 for a reduced blur or 150 for an increased blur.

By default, the mask is made from the magnitude of the slopes of a grayscale version of the input, where the slopes are found by the comet blur method. However, a user-supplied mask can be used instead.

There are eight basic modes of operation:

  1. blur non-edges in a direction parallel to contours
  2. blur non-edges in a direction perpendicular to contours
  3. blur edges in a direction parallel to contours
  4. blur edges in a direction perpendicular to contours
  5. sharpen non-edges in a direction parallel to contours
  6. sharpen non-edges in a direction perpendicular to contours
  7. sharpen edges in a direction parallel to contours
  8. sharpen edges in a direction perpendicular to contours
Parallel Perpendicular

Blur non-edges (default)

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_ex1.png
 acbs_ex1.pngjpg

Blur non-edges (default)

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_ex1t.png . . . . . ^
  perpendicular
 acbs_ex1t.pngjpg

Blur the edges

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_ex2.png E
 acbs_ex2.pngjpg

Blur the edges

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_ex2t.png E . . . . ^
  Perpendicular
 acbs_ex2t.pngjpg

Sharpen non-edges

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_ex3.png . . . -100
 acbs_ex3.pngjpg

Sharpen non-edges

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_ex3t.png . . . -100 . ^
  Perpendicular
 acbs_ex3t.pngjpg

Sharpen the edges

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_ex4.png E . . -100
 acbs_ex4.pngjpg

Sharpen the edges

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_ex4t.png E . . -100 . ^
  Perpendicular
 acbs_ex4t.pngjpg

Over-sharpen the non-edges

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_ex5.png N . . -200
 acbs_ex5.pngjpg

Over-sharpen the non-edges

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_ex5t.png N . . -200 . ^
  Perpendicular
 acbs_ex5t.pngjpg

Over-sharpen the edges

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_ex6.png E . . -200
 acbs_ex6.pngjpg

Over-sharpen the edges

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_ex6t.png E . . -200 . ^
  Perpendicular
 acbs_ex6t.pngjpg

The effect is generally strongest when it is perpendicular to contours. For example, blurring an edge in a direction along that edge doesn't change it, but blurring an edge perpendicular to the edge has a strong effect.

Over-sharpening causes pixels to exceed the range 0 to 100%, which is usually clipped. We can use Limit min-max to prevent pixel values being pushed outside the range of a local window:

call %PICTBAT%limitMinMax ^
  toes.png ^
  acbs_ex6t.png ^
  acbs_ex6t_lmm.png ^
  20x20
 acbs_ex6t_lmm.pngjpg

The large window has created homogeneity on each side of edges. This can be reduced by setting a blend percentage less than 100%. 

call %PICTBAT%limitMinMax ^
  toes.png ^
  acbs_ex6t.png ^
  acbs_ex6t_lmm.png ^
  20x20 ^
  80
 acbs_ex6t_lmm.pngjpg

Mask

The mask for this effect has equal red and green channels that represent the magnitude of the effect, and a blue channel that represents the direction of the effect.

Instead of the default mask (and default processing of that mask), the user can supply a mask:

Make a mask

%IMG7%magick ^
  -size 267x233 ^
  radial-gradient: ^
  ( +clone ) ^
  gradient: ^
  -combine ^
  -set colorspace sRGB ^
  acbs_radmask.png
 acbs_radmask.png

Apply the mask

set acbsRD_MASK=acbs_radmask.png

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_rm1.png

set acbsRD_MASK=
 acbs_rm1.pngjpg

Apply the mask, blurring the "edges"
(where the mask is white)

set acbsRD_MASK=acbs_radmask.png

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_rm2.png E

set acbsRD_MASK=
 acbs_rm2.pngjpg

Sigmas

There are two sigma controls: one for the edge detector, and one for the actual blur.

Large values for the edge detector don't work well:

Blur non-edges

set acbsWR_MASK=acbs_msk_s1.png

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_s1.png N 30

set acbsWR_MASK=
 acbs_s1.pngjpg acbs_msk_s1.pngjpg

The mask from a comet blur is streaky. We can blur before the stretch to remove the streaks, and after to smooth the boundary:

Blur non-edges

set acbsWR_MASK=acbs_msk_s2.png
set acbsMSK_PROC=-blur 0x5 -contrast-stretch 40%%x50%% -blur 0x5

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_s2.png N 10 15

set acbsMSK_PROC=
set acbsWR_MASK=
 acbs_s2.pngjpg acbs_msk_s2.pngjpg

A blur sigma around half the edge detector sigma works well. Larger blur sigmas, with no special processing, create artifacts:

Blur non-edges

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_s2x.png N 10 15
 acbs_s2x.pngjpg

We can reduce the artifacts by limiting:

call %PICTBAT%limitMinMax ^
  %SRC% ^
  acbs_s2x.png ^
  acbs_s2x_lmm.png ^
  5x5
 acbs_s2x_lmm.pngjpg

Colorspace

Any operation that mixes colours from a number of pixels, such as blur and sharpen, is more correctly done in linear colorspace. (Well, that should read scene-referred colorspace, but we assume linear is a good approximation.)

call %PICTBAT%acbs_colsp %SRC%
Colorspace blur non-edges blur edges sharpen non-edges sharpen edges
sRGB acbs_csnb_sRGB.pngjpg acbs_cseb_sRGB.pngjpg acbs_csns_sRGB.pngjpg acbs_cses_sRGB.pngjpg
RGB acbs_csnb_RGB.pngjpg acbs_cseb_RGB.pngjpg acbs_csns_RGB.pngjpg acbs_cses_RGB.pngjpg
Lab acbs_csnb_Lab.pngjpg acbs_cseb_Lab.pngjpg acbs_csns_Lab.pngjpg acbs_cses_Lab.pngjpg

There is practically no difference between the colorspace versions.

Blur and sharpen

We can call the script to blur, and call it again to sharpen that result:

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_bands.png

call %PICTBAT%adapContBlrShp ^
  acbs_bands.png ^
  acbs_bands.png E . . -100
 acbs_bands.pngjpg

Or sharpen the blurred non-edges

call %PICTBAT%adapContBlrShp ^
  acbs_bands.png ^
  acbs_bandsne.png N . . ^
  -100 . perpendicular
 acbs_bandsne.pngjpg

Or we can save the mask used in the blur, and use the same mask for sharpening.

set acbsWR_MASK=acbs_msk.png

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_bands2.png

set acbsWR_MASK=

We show the intermediate result and the mask.

 acbs_bands2.pngjpg acbs_msk.pngjpg 
set acbsRD_MASK=acbs_msk.png

call %PICTBAT%adapContBlrShp ^
  acbs_bands2.png ^
  acbs_bands2s.png E . . ^
  -100 . perpendicular

set acbsRD_MASK=
 acbs_bands2s.pngjpg

The default settings give a fairly sharp line between the blurred and sharpened areas. We can cure this by setting acbsMSK_PROC: 

set acbsMSK_PROC=-contrast-stretch 40%%x40%% -blur 0x5
set acbsWR_MASK=acbs_msk3.png

call %PICTBAT%adapContBlrShp ^
  %SRC% ^
  acbs_bands3.png

set acbsWR_MASK=
set acbsMSK_PROC=

We show the intermediate result and the mask.

 acbs_bands3.pngjpg acbs_msk3.pngjpg 
set acbsRD_MASK=acbs_msk3.png

call %PICTBAT%adapContBlrShp ^
  acbs_bands3.png ^
  acbs_bands3s.png E . . ^
  -100 . perpendicular

set acbsRD_MASK=
 acbs_bands3s.pngjpg

Scripts

For convenience, .bat scripts are also available in a single zip file. See Zipped BAT files.

adapContBlrShp.bat 

rem From image %1,
rem makes output %2
rem blurred or sharpened parallel to contours
rem with most effect at edges, or most at non-edges.
rem %3 E=blur at the edges, or N=blur at non-edges.
rem %4 edge detector sigma
rem %5 blur sigma
rem %6 blend percentage: 0=no effect, 100=blur, -100=sharpen
rem %7 colorspace
rem %8 parallel or perpendicular
@rem
@rem Also uses:
@rem   acbsWR_MASK if not blank, writes mask to this file
@rem   acbsRD_MASK if not blank, reads mask from this file
@rem   acbsMSK_PROC
@rem   acbsMSK_PRE
@rem
@rem Updated:
@rem   16-December-2017 Corrected PREV_COLSP bug.
@rem   29-August-2022 for IM v7.
@rem

@if "%1"=="" findstr /B "rem @rem" %~f0 & exit /B 1

@setlocal enabledelayedexpansion

rem @call echoOffSave

call %PICTBAT%setInOut %1 acbs

if not "%2"=="" if not "%2"=="." set OUTFILE=%2

set BLR_AT=%3
if "%BLR_AT%"=="." set BLR_AT=
if "%BLR_AT%"=="" set BLR_AT=N

set EDGE_SIG=%4
if "%EDGE_SIG%"=="." set EDGE_SIG=
if "%EDGE_SIG%"=="" set EDGE_SIG=10

set BLUR_SIG=%5
if "%BLUR_SIG%"=="." set BLUR_SIG=
if "%BLUR_SIG%"=="" set /A BLUR_SIG=%EDGE_SIG%/2

set BLEND_PC=%6
if "%BLEND_PC%"=="." set BLEND_PC=
if "%BLEND_PC%"=="" set BLEND_PC=100

set COLSP=%7
if "%COLSP%"=="." set COLSP=

set PARPERP=%8
if "%PARPERP%"=="." set PARPERP=
if "%PARPERP%"=="" set PARPERP=parallel

set TMPDIR=\temp\
set TMPGRAY=%TMPDIR%acbs_gray.miff
set TMPDIRN=%TMPDIR%acbs_gray_dirn.miff
set TMPMAG=%TMPDIR%acbs_gray_mag.miff
set TMPMASK=%TMPDIR%acbs_gray_mask.miff

if /I "%BLR_AT%"=="E" (
  set sNEG=
) else if /I "%BLR_AT%"=="N" (
  set sNEG=-channel RG -negate +channel
) else (
  echo Bad BLR_AT [%BLR_AT%] should be E or N.
  exit /B 1
)

:: FIXME: One of these is wrong
if /I "%PARPERP%"=="Parallel" (
  set sBLRARG=-set option:compose:args %BLUR_SIG%x0+0+360
) else if /I "%PARPERP%"=="Perpendicular" (
  set sBLRARG=-set option:compose:args 0x%BLUR_SIG%+0+360
) else (
  echo Bad PARPERP [%PARPERP%] should be Parallel or Perpendicular.
  exit /B 1
)

if "%acbsMSK_PROC%"=="" set acbsMSK_PROC=-contrast-stretch 45%%x45%%
if "%acbsMSK_PROC%"=="." set acbsMSK_PROC=

if "%acbsRD_MASK%"=="" (
  set sRD_MASK=%TMPMAG% -auto-level %acbsMSK_PROC%
  set sRD_MASK=%TMPMASK% -auto-level %acbsMSK_PROC%
) else (
  set sRD_MASK=%acbsRD_MASK%
)

if "%acbsWR_MASK%"=="" (
  set sWR_MASK=
) else (
  set sWR_MASK=+write %acbsWR_MASK%
)


set PREV_COLSP=
for /F "usebackq" %%L in (`%IMG7%magick ^
  %INFILE% ^
  -format "PREV_COLSP=%%[colorspace]" +write info: ^
  -colorspace Gray ^
  %acbsMSK_PRE% ^
  %TMPGRAY%`) do set %%L
if "%PREV_COLSP%"=="" exit /B 1
echo PREV_COLSP=%PREV_COLSP%

set COLSP_IN=
set COLSP_OUT=
if "%COLSP%" NEQ "" if /I "%COLSP%" NEQ "%PREV_COLSP%" (
  set COLSP_IN=-colorspace %COLSP% -set colorspace sRGB
  set COLSP_OUT=-set colorspace %COLSP% -colorspace %PREV_COLSP%
)

call %PICTBAT%slopeXYbl ^
  %TMPGRAY% %TMPGRAY% %EDGE_SIG%

call %PICTBAT%slopeXYmag ^
  %TMPGRAY% %TMPMAG%

call %PICTBAT%slopeXYdirn ^
  %TMPGRAY% %TMPDIRN% ^
  SWAP . 75

%IMG7%magick ^
  %TMPMAG% -auto-level %acbsMSK_PROC% ^
  ( +clone ) ^
  %TMPDIRN% ^
  -combine ^
  -set colorspace sRGB ^
  +depth ^
  -depth 32 ^
  -define "quantum:format=floating-point" ^
  %TMPMASK%

%IMG7%magick ^
  %INFILE% ^
  %COLSP_IN% ^
  ( +clone ^
    ( %sRD_MASK% ^
      %sWR_MASK% ^
      %sNEG% ^
    ) ^
    -compose Blur ^
    %sBLRARG% ^
    -composite ^
  ) ^
  -compose Blend -define compose:args=%BLEND_PC% -composite ^
  %COLSP_OUT% ^
  +depth ^
  -depth 32 ^
  -define "quantum:format=floating-point" ^
  %OUTFILE%

if ERRORLEVEL 1 exit /B 1


call echoRestore

@endlocal & set acbsOUTFILE=%OUTFILE%

All images on this page were created by the commands shown, using:

%IMG7%magick -version
Version: ImageMagick 7.1.0-42 Q16-HDRI x64 396d87c:20220709 https://imagemagick.org
Copyright: (C) 1999 ImageMagick Studio LLC
License: https://imagemagick.org/script/license.php
Features: Cipher DPC HDRI OpenCL 
Delegates (built-in): bzlib cairo freetype gslib heic jng jp2 jpeg jxl lcms lqr lzma openexr pangocairo png ps raqm raw rsvg tiff webp xml zip zlib
Compiler: Visual Studio 2022 (193231332)

To improve internet download speeds, some images may have been automatically converted (by ImageMagick, of course) from PNG or TIFF or MIFF to JPG.

Source file for this web page is adapcontblrshp.h1. To re-create this web page, execute "procH1 adapcontblrshp".

This page, including the images, is my copyright. Anyone is permitted to use or adapt any of the code, scripts or images for any purpose, including commercial use.

Anyone is permitted to re-publish this page, but only for non-commercial use.

Anyone is permitted to link to this page, including for commercial use.

Page version v1.0 4-December-2017.

Page created 29-Aug-2022 04:43:58.

Copyright © 2022 Alan Gibson.