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I want to get some pixels from my image and print it out to the screen. My attempt is like this:

const MagickCore::Quantum *pixelsArr = image1->getConstPixels( 0, 0, 800, 600 );
unsigned char r = pixelsArr[ 0 ].red * 255 / QuantumRange;
unsigned char g = pixelsArr[ 0 ].greenQuantum * 255 / QuantumRange;

but I get error:

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first.cpp:726:38: error: member reference base type 'const MagickCore::Quantum' (aka 'const float') is not a structure or union
                                        unsigned char r = pixelsArr[ i ].red * 255 / QuantumRange;
                                                          ~~~~~~~~~~~~~~^~~~
first.cpp:727:38: error: member reference base type 'const MagickCore::Quantum' (aka 'const float') is not a structure or union
                                        unsigned char g = pixelsArr[ i ].redQuantum * 255 / QuantumRange;

How to convert this float (which called Quantum) to R/G/B components?
IM: is up to date, OS X 10.12.3.

Is the RGB order just goes like this in my pixelsArr?

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R G B R G B R G B R G B....

and every R, G, B is of a quantum type

In other words for RGB image I should go this way:

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const MagickCore::Quantum *pixelsArr = image->getConstPixels( 0, 0, _imgWidth, _imgHeight );
for ( unsigned int i = 0; i < _imgWidth * _imgHeight * 3; i += 3 ) {
	for ( unsigned int i1 = 0; i1 < 2; i1++ ) {
		unsigned char r = pixelsArr[ i + 0 ] * 255 / QuantumRange;
		unsigned char g = pixelsArr[ i + 1 ] * 255 / QuantumRange;
		unsigned char b = pixelsArr[ i + 2 ] * 255 / QuantumRange;
Am I right or not?


    
     
      
       
        
         snibgo
        
        wrote:
        
         ↑
        
        
         2017-03-31T19:15:26-07:00
        
       
       getConstPixels() is declared in Image.h. It returns "PixelPacket *", which is not the same thing as "Quantum *".
It doesn't look that it's the same thing:
       

       
        
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        const MagickCore::PixelPacket *pixelsArr = image->getConstPixels( 0, 0, _imageWidth, _imageHeight );
       
       
        
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        first.cpp:723:36: error: cannot initialize a variable of type 'const MagickCore::PixelPacket *' (aka 'const MagickCore::_PixelPacket *') with an rvalue of type
      'const Quantum *' (aka 'const float *')
                                const MagickCore::PixelPacket *pixelsArr = image->getConstPixels( 0, 0, _imageWidth, _imageHeight );
                                                               ^           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.
What's wrong with my code?

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$ magick -version
Version: ImageMagick 7.0.5-2 Q16 x86_64 2017-03-11 http://www.imagemagick.org
License: http://www.imagemagick.org/script/license.php
Features: Cipher DPC HDRI Modules 
Delegates (built-in): bzlib freetype jng jpeg ltdl lzma png tiff xml zlib
       
       
        
         Ah, you are using v7? getConstPixels() changed from v6. In v6, it returns PixelPacket*. In v7, it returns Quantum*.
         

         When asking questions, please always state the version of IM you are using.
         

         Sorry, I don't use Magick++ or MacickWand in v7. But you can see how getConstPixels is used, by an example in Image.cpp. You can call GetPixelInfoPixel to convert the returned Quantum* to an object of type PixelInfo.
         

         The type PixelInfo is defined in MagickCore\pixel.h. This has element red, green, blue and many others.
        
        
         Instead of that I use this approach:
         

         
          
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          for ( unsigned int j = 0; j < _height; j++ ) {
	for ( unsigned int i = 0; i < _width; i++ ) {
		Magick::Color c = image->pixelColor( i, j );
		unsigned char r = c.quantumRed() * 255 / QuantumRange;
		unsigned char g = c.quantumGreen() * 255 / QuantumRange;
		unsigned char b = c.quantumBlue() * 255 / QuantumRange;
it's very usable way of getting a pixel color for me!
         
         
          
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