@ -12,7 +12,8 @@ using SixLabors.Primitives;
namespace SixLabors.ImageSharp.Processing.Processors.Normalization
{
/// <summary>
/// Applies an adaptive histogram equalization to the image.
/// Applies an adaptive histogram equalization to the image. The image is split up in tiles. For each tile a cumulative distribution function (cdf) is calculated.
/// To calculate the final equalized pixel value, the cdf value of four adjacent tiles will be interpolated.
/// </summary>
/// <typeparam name="TPixel">The pixel format.</typeparam>
internal class AdaptiveHistEqualizationProcessor < TPixel > : HistogramEqualizationProcessor < TPixel >
@ -55,52 +56,17 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
int halfTileWidth = tileWidth / 2 ;
int halfTileHeight = tileHeight / 2 ;
var cdfData = new CdfData [ numTilesX , numTilesY ] ;
using ( System . Buffers . IMemoryOwner < int > histogramBuffer = memoryAllocator . Allocate < int > ( this . LuminanceLevels , AllocationOptions . Clean ) )
using ( System . Buffers . IMemoryOwner < int > cdfBuffer = memoryAllocator . Allocate < int > ( this . LuminanceLevels , AllocationOptions . Clean ) )
{
Span < int > histogram = histogramBuffer . GetSpan ( ) ;
Span < int > cdf = cdfBuffer . GetSpan ( ) ;
// The image is split up into square tiles of the size of the parameter GridSize.
// For each tile the cumulative distribution function will be calculated.
// The image is split up into tiles. For each tile the cumulative distribution function will be calculated.
CdfData [ , ] cdfData = this . CalculateLookupTables ( source , histogram , cdf , numTilesX , numTilesY , tileWidth , tileHeight ) ;
int tileX = 0 ;
int tileY = 0 ;
for ( int y = 0 ; y < source . Height ; y + = tileHeight )
{
tileX = 0 ;
for ( int x = 0 ; x < source . Width ; x + = tileWidth )
{
histogram . Clear ( ) ;
cdf . Clear ( ) ;
int ylimit = Math . Min ( y + tileHeight , source . Height ) ;
int xlimit = Math . Min ( x + tileWidth , source . Width ) ;
for ( int dy = y ; dy < ylimit ; dy + + )
{
for ( int dx = x ; dx < xlimit ; dx + + )
{
int luminace = this . GetLuminance ( source [ dx , dy ] , this . LuminanceLevels ) ;
histogram [ luminace ] + + ;
}
}
if ( this . ClipHistogramEnabled )
{
this . ClipHistogram ( histogram , this . ClipLimitPercentage , pixelsInTile ) ;
}
int cdfMin = this . CalculateCdf ( cdf , histogram , histogram . Length - 1 ) ;
var currentCdf = new CdfData ( cdf . ToArray ( ) , cdfMin ) ;
cdfData [ tileX , tileY ] = currentCdf ;
tileX + + ;
}
tileY + + ;
}
tileX = 0 ;
tileY = 0 ;
for ( int y = halfTileHeight ; y < source . Height - tileHeight ; y + = tileHeight )
{
tileX = 0 ;
@ -128,7 +94,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
float cdfRightTopLuminance = cdfData [ xRight , yTop ] . RemapGreyValue ( luminace , pixelsInTile ) ;
float cdfLeftBottomLuminance = cdfData [ xLeft , yBottom ] . RemapGreyValue ( luminace , pixelsInTile ) ;
float cdfRightBottomLuminance = cdfData [ xRight , yBottom ] . RemapGreyValue ( luminace , pixelsInTile ) ;
float luminanceEqualized = this . BilinearInterpolation ( tilePosX , tilePosY , tilePosX / ( float ) ( tileWidth - 1 ) , ty , cdfLeftTopLuminance , cdfRightTopLuminance , cdfLeftBottomLuminance , cdfRightBottomLuminance ) ;
float luminanceEqualized = this . BilinearInterpolation ( tilePosX / ( float ) ( tileWidth - 1 ) , ty , cdfLeftTopLuminance , cdfRightTopLuminance , cdfLeftBottomLuminance , cdfRightBottomLuminance ) ;
pixels [ ( dy * source . Width ) + dx ] . PackFromVector4 ( new Vector4 ( luminanceEqualized ) ) ;
tilePosX + + ;
@ -145,11 +111,62 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
}
}
/// <summary>
/// Calculates the lookup tables for each tile of the image.
/// </summary>
/// <param name="source">The input image for which the tiles will be calculated.</param>
/// <param name="histogram">Histogram buffer.</param>
/// <param name="cdf">Buffer for calculating the cumulative distribution function.</param>
/// <param name="numTilesX">Number of tiles in the X Direction.</param>
/// <param name="numTilesY">Number of tiles in Y Direction</param>
/// <param name="tileWidth">Width in pixels of one tile.</param>
/// <param name="tileHeight">Height in pixels of one tile.</param>
/// <returns>All lookup tables for each tile in the image.</returns>
private CdfData [ , ] CalculateLookupTables ( ImageFrame < TPixel > source , Span < int > histogram , Span < int > cdf , int numTilesX , int numTilesY , int tileWidth , int tileHeight )
{
var cdfData = new CdfData [ numTilesX , numTilesY ] ;
int pixelsInTile = tileWidth * tileHeight ;
int tileX = 0 ;
int tileY = 0 ;
for ( int y = 0 ; y < source . Height ; y + = tileHeight )
{
tileX = 0 ;
for ( int x = 0 ; x < source . Width ; x + = tileWidth )
{
histogram . Clear ( ) ;
cdf . Clear ( ) ;
int ylimit = Math . Min ( y + tileHeight , source . Height ) ;
int xlimit = Math . Min ( x + tileWidth , source . Width ) ;
for ( int dy = y ; dy < ylimit ; dy + + )
{
for ( int dx = x ; dx < xlimit ; dx + + )
{
int luminace = this . GetLuminance ( source [ dx , dy ] , this . LuminanceLevels ) ;
histogram [ luminace ] + + ;
}
}
if ( this . ClipHistogramEnabled )
{
this . ClipHistogram ( histogram , this . ClipLimitPercentage , pixelsInTile ) ;
}
int cdfMin = this . CalculateCdf ( cdf , histogram , histogram . Length - 1 ) ;
var currentCdf = new CdfData ( cdf . ToArray ( ) , cdfMin ) ;
cdfData [ tileX , tileY ] = currentCdf ;
tileX + + ;
}
tileY + + ;
}
return cdfData ;
}
/// <summary>
/// Bilinear interpolation between four tiles.
/// </summary>
/// <param name="x">X position.</param>
/// <param name="y">Y position.</param>
/// <param name="tx">The interpolation value in x direction in the range of [0, 1].</param>
/// <param name="ty">The interpolation value in y direction in the range of [0, 1].</param>
/// <param name="lt">Luminance from top left tile.</param>
@ -157,7 +174,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
/// <param name="lb">Luminance from left bottom tile.</param>
/// <param name="rb">Luminance from right bottom tile.</param>
/// <returns>Interpolated Luminance.</returns>
private float BilinearInterpolation ( int x , int y , float tx , float ty , float lt , float rt , float lb , float rb )
private float BilinearInterpolation ( float tx , float ty , float lt , float rt , float lb , float rb )
{
return this . LinearInterpolation ( this . LinearInterpolation ( lt , rt , tx ) , this . LinearInterpolation ( lb , rb , tx ) , ty ) ;
}
popow
8 years ago