How to fill a primitive with a gradient color?
Posted: 2017-04-20T12:35:57-07:00
Is there a way to fill a primitive with a gradient color?
Legacy ImageMagick Discussions Archive
Use https://github.com/ImageMagick/ImageMagick/discussions instead.
https://imagemagick.com/discourse-server/
How to fill a primitive with a gradient color?
https://imagemagick.com/discourse-server/viewtopic.php?t=31808
Page 1 of 1
Re: How to fill a primitive with a gradient color?
Posted: 2017-04-20T13:01:54-07:00
Not directly. It can be made transparent, and the image then composited over a gradient image.
Re: How to fill a primitive with a gradient color?
Posted: 2017-04-21T08:11:59-07:00
Such an interesting technique. You mean I can draw a primitive with a transparent fill and put that primitive over the gradient image? Do I need to have a white background outside the primitive? Then how to draw two or more primitives with different gradients on the same image?
Re: How to fill a primitive with a gradient color?
Posted: 2017-04-21T10:01:57-07:00
An example may clarify.
This makes a gradient, then a same-size image with a white polygon (a triangle) on black background, and this is applied as opacity to the gradient. The result is a gradient triangle of transparent background.
We repeat this with a second triangle.
Then we composite the second triangle over the first.
I expect there are other ways of doing this.
Code: Select all
%IM%convert ^
( ^
-size 300x300 gradient:red-blue ^
( +clone -fill Black -colorize 100 ^
-fill White -draw "polygon 50,50 250,50 200,200" ^
) ^
-alpha off ^
-compose CopyOpacity -composite ^
) ^
( ^
-size 300x300 gradient:#f80-#08f ^
( +clone -fill Black -colorize 100 ^
-fill White -draw "polygon 50,150 250,150 200,300" ^
) ^
-alpha off ^
-compose CopyOpacity -composite ^
) ^
-compose Over -composite ^
grad_shapes.pngThis makes a gradient, then a same-size image with a white polygon (a triangle) on black background, and this is applied as opacity to the gradient. The result is a gradient triangle of transparent background.
We repeat this with a second triangle.
Then we composite the second triangle over the first.
I expect there are other ways of doing this.
Re: How to fill a primitive with a gradient color?
Posted: 2017-04-21T13:20:59-07:00
Wow that works really cool but how to convert it to Magick++ format? 
The first problem is with the colorize function. I see two definitions of colorize function:
how to properly do that step?
The first problem is with the colorize function. I see two definitions of colorize function:
Code: Select all
// Colorize image with pen color, using specified percent alpha.
void colorize(const unsigned int alpha_,const Color &penColor_);
// Colorize image with pen color, using specified percent alpha
// for red, green, and blue quantums
void colorize(const unsigned int alphaRed_,const unsigned int alphaGreen_,
const unsigned int alphaBlue_,const Color &penColor_);
Code: Select all
-colorize 100Re: How to fill a primitive with a gradient color?
Posted: 2017-04-21T14:15:10-07:00
"-fill Black -colorize 100" simply makes all the pixels opaque black. It's a slightly clumsy way of doing it at the command line. In the C APIs, there are cleaner ways. I don't use Magick++, but "erase" looks likely, after setting the background colour.
Re: How to fill a primitive with a gradient color?
Posted: 2017-04-21T15:22:24-07:00
1. What do the "-alpha off" command do? Is it just remove the alpha channel from an image?
2. I try to convert it to C++ so I did:
it looks like ColorizeCompositeOp is not the right operator for achieving this goal I don't know what's the CopyOpacity operator? In the include.h I see only these compose operators:
2. I try to convert it to C++ so I did:
Code: Select all
Magick::Image gradImg( Magick::Geometry( 500, 500 ), Magick::Color( "white" ) );
gradImg.read( "gradient:red-blue" );
Magick::Image testImg( Magick::Geometry( 500, 500 ), Magick::Color( "black" ) );
testImg.strokeWidth( 0 );
testImg.fillColor( Magick::Color( QuantumRange, QuantumRange, QuantumRange, QuantumRange ) ); // white color!
float centerX = 250, centerY = 250;
float xr = 150, yr = 150;
testImg.draw( Magick::DrawableEllipse( centerX, centerY, xr, yr, 0, 360 ) );
gradImg.composite( testImg, gradImg.columns() / 2 - testImg.columns() / 2, gradImg.rows() / 2 - testImg.rows() / 2, Magick::ColorizeCompositeOp );
gradImg.write( "images/grad.png" );
testImg.write( "images/test2.png" );
Code: Select all
// Composition operations
using MagickCore::CompositeOperator;
using MagickCore::AlphaCompositeOp;
using MagickCore::AtopCompositeOp;
using MagickCore::BlendCompositeOp;
using MagickCore::BlurCompositeOp;
using MagickCore::BumpmapCompositeOp;
using MagickCore::ChangeMaskCompositeOp;
using MagickCore::ClearCompositeOp;
using MagickCore::ColorBurnCompositeOp;
using MagickCore::ColorDodgeCompositeOp;
using MagickCore::ColorizeCompositeOp;
using MagickCore::CopyBlackCompositeOp;
using MagickCore::CopyBlueCompositeOp;
using MagickCore::CopyCompositeOp;
using MagickCore::CopyCyanCompositeOp;
using MagickCore::CopyGreenCompositeOp;
using MagickCore::CopyMagentaCompositeOp;
using MagickCore::CopyAlphaCompositeOp;
using MagickCore::CopyRedCompositeOp;
using MagickCore::CopyYellowCompositeOp;
using MagickCore::DarkenCompositeOp;
using MagickCore::DarkenIntensityCompositeOp;
using MagickCore::DifferenceCompositeOp;
using MagickCore::DisplaceCompositeOp;
using MagickCore::DissolveCompositeOp;
using MagickCore::DistortCompositeOp;
using MagickCore::DivideDstCompositeOp;
using MagickCore::DivideSrcCompositeOp;
using MagickCore::DstAtopCompositeOp;
using MagickCore::DstCompositeOp;
using MagickCore::DstInCompositeOp;
using MagickCore::DstOutCompositeOp;
using MagickCore::DstOverCompositeOp;
using MagickCore::ExclusionCompositeOp;
using MagickCore::HardLightCompositeOp;
using MagickCore::HardMixCompositeOp;
using MagickCore::HueCompositeOp;
using MagickCore::InCompositeOp;
using MagickCore::IntensityCompositeOp;
using MagickCore::LightenCompositeOp;
using MagickCore::LightenIntensityCompositeOp;
using MagickCore::LinearBurnCompositeOp;
using MagickCore::LinearDodgeCompositeOp;
using MagickCore::LinearLightCompositeOp;
using MagickCore::LuminizeCompositeOp;
using MagickCore::MathematicsCompositeOp;
using MagickCore::MinusDstCompositeOp;
using MagickCore::MinusSrcCompositeOp;
using MagickCore::ModulateCompositeOp;
using MagickCore::ModulusAddCompositeOp;
using MagickCore::ModulusSubtractCompositeOp;
using MagickCore::MultiplyCompositeOp;
using MagickCore::NoCompositeOp;
using MagickCore::OutCompositeOp;
using MagickCore::OverCompositeOp;
using MagickCore::OverlayCompositeOp;
using MagickCore::PegtopLightCompositeOp;
using MagickCore::PinLightCompositeOp;
using MagickCore::PlusCompositeOp;
using MagickCore::ReplaceCompositeOp;
using MagickCore::SaturateCompositeOp;
using MagickCore::ScreenCompositeOp;
using MagickCore::SoftLightCompositeOp;
using MagickCore::SrcAtopCompositeOp;
using MagickCore::SrcCompositeOp;
using MagickCore::SrcInCompositeOp;
using MagickCore::SrcOutCompositeOp;
using MagickCore::SrcOverCompositeOp;
using MagickCore::ThresholdCompositeOp;
using MagickCore::UndefinedCompositeOp;
using MagickCore::VividLightCompositeOp;
using MagickCore::XorCompositeOp;
Re: How to fill a primitive with a gradient color?
Posted: 2017-04-21T15:42:22-07:00
For translating between command-line and C (or C++), a very useful source is MagickCore\option.c. This file translates command-line options to the internals. Search that file for "CopyOpacity".
Re: How to fill a primitive with a gradient color?
Posted: 2017-04-21T16:00:49-07:00
Thanks, it's very useful file!
Didn't know about it. Now I know that ColorizeCompositeOp is the "Magick::CopyAlphaCompositeOp". Now I don't know how to do: "-alpha off" Why do you do this step?Re: How to fill a primitive with a gradient color?
Posted: 2017-04-21T17:54:48-07:00
"CopyOpacity" normally copies the opacity from Src to Dst. If Src is fully opaque, this would make the result white. But if alpha is off, it doesn't copy the opacity; instead, it copies the intensity of Src to the opacity of Dst.
I think "-alpha off" is "MagickSetImageAlphaChannel (wand, OffAlphaChannel)". In v7, traits should probably be used.
I think "-alpha off" is "MagickSetImageAlphaChannel (wand, OffAlphaChannel)". In v7, traits should probably be used.
Re: How to fill a primitive with a gradient color?
Posted: 2017-04-21T17:57:03-07:00
Oh finally I've got it. You mean simply masks technique. Now I understand what did you mean.
Here is the way for doing this:
Looks like all work fine Thank you!
Here is the way for doing this:
Code: Select all
Magick::Image gradImg( Magick::Geometry( 500, 500 ), Magick::Color( "white" ) );
gradImg.read( "gradient:red-blue" );
Magick::Image maskImg( Magick::Geometry( 500, 500 ), Magick::Color( "black" ) );
maskImg.strokeWidth( 0 );
maskImg.fillColor( Magick::Color( "white" ) ); // white color!
maskImg.draw( Magick::DrawableEllipse( 250, 250, 150, 150, 0, 360 ) );
maskImg.alphaChannel( MagickCore::DeactivateAlphaChannel );
gradImg.alphaChannel( MagickCore::DeactivateAlphaChannel );
maskImg.negate();
gradImg.composite( maskImg, 0, 0, Magick::BlendCompositeOp ); // applying a mask
gradImg.write( "images/grad.png" );
maskImg.write( "images/mask.png" );