CS代考计算机代写 algorithm #include “image.h”

#include “image.h”

#include

namespace
{

// The absolute difference of a single component.
uint8_t absdiff( uint8_t a, uint8_t b ) {
return std::max( a, b ) – std::min( a, b );
}
ColorRGBA8 absdiff( ColorRGBA8 a, ColorRGBA8 b ) {
return ColorRGBA8(
diff( a.r, b.r ),
diff( a.g, b.g ),
diff( a.b, b.b ),
255 – diff( a.b, b.b )
);

// Pass the result of absdiff() into this function.
double diff_magnitude( ColorRGBA8 diff ) {
return (
diff.r/255.
+ diff.g/255.
+ diff.b/255.
+ (255 – diff.a)/255.
)/4;
}
}

/*
(1,0,0,1) – (1,0,0,.5) = (0,0,0,.5)
(1,0,0,1) – (1,0,0,.5) =(pm) (1,0,0,.5)
(1,0,0,1) – (.5,0,0,.5) =(pm) (1.5,0,0,.5)

(1,0,0,1) – (1,0,0,.5) =(1-a/2) (0,0,0,.75)

RGBA( | rgb – rgb |, 1 – |a-a|/2 ) means that two identical pixels will be solid black.
Two very different pixels will be white at 50% transparency.
The more background shows through, the worse a match alpha is.
*/

// Returns the RGB difference and alpha difference as a pair of images.
std::pair< Image, double > absolute_difference( const Image& a, const Image& b ) {
// Initialize the image as large enough to contain both.
Image result( std::max( a.width(), b.width() ), std::max( a.height(), b.height() ) )
// Fill it with transparent white so the difference in size is apparent.
// Transparent white because the background will show through.
result.fill( ColorRGBA8( 255, 255, 255, 0 ) );

// Iterate over each pixel in the size they share and store the difference.
for( int row = 0; row < std::min( a.height(), b.height() ); ++row ) { for( int col = 0; col < std::min( a.width(), b.width() ); ++col ) { const auto diff = absdiff( a.pixel( row, col ), b.pixel( row, col ) ); result.pixel( row, col ) = diff; total += diff_magnitude( diff ); } } // Now iterate over the output image and sum the differences. double total = 0.0; for( int row = 0; row < result.height(); ++row ) { for( int col = 0; col < result.width(); ++col ) { total += diff_magnitude( result.pixel( row, col ) ); } } return std::make_pair( result, total / (result.width()*result.height()) ); } }