iOS,OC,图片相似度比较,图片指纹

上周，正在忙，突然有个同学找我帮忙，说有个需求：图片相似度比较。

网上搜了一下，感觉不是很难，就写了下，这里分享给需要的小伙伴。

首先，本次采用的是OpenCV，图片哈希值：

先说一下基本思路：

1.      缩小尺寸：将图像缩小到8*8的尺寸，总共64个像素。这一步的作用是去除图像的细节，只保留结构/明暗等基本信息，摒弃不同尺寸/比例带来的图像差异；

注：实际操作时，采取了两种尺寸作对比（10*10，100*100）尺寸再大的话就会性能影响就会较大了，我实现了两种，目的是为了展示怎么设定不同尺寸。

2.      简化色彩：将缩小后的图像，转为64级灰度，即所有像素点总共只有64种颜色；

注：关于多少灰度级的问题，我并没有太在意，采取了一个合适的RGB to GRAY 算法就好，个人理解

3.      计算平均值：计算所有64个像素的灰度平均值；

4.      比较像素的灰度：将每个像素的灰度，与平均值进行比较，大于或等于平均值记为1，小于平均值记为0；

5.      计算哈希值：将上一步的比较结果，组合在一起，就构成了一个64位的整数，这就是这张图像的指纹。组合的次序并不重要，只要保证所有图像都采用同样次序就行了；

6.      得到指纹以后，就可以对比不同的图像

参考博客：http://blog.csdn.net/fengbingchun/article/details/42153261

类文件下载链接：http://files.cnblogs.com/files/kongkaikai/GetSimilarity.zip

GetSimilarity.h

 //
 //  GetSimilarity.h
 //  imgsimlartest
 //
 //  Created by test on 16/3/3.
 //  Copyright © 2016年 com.facishare.CoreTest. All rights reserved.
 //

 #import <Foundation/Foundation.h>
 #import <UIKit/UIKit.h>
 typedef double Similarity;

 @interface GetSimilarity : NSObject
 - (void)setImgWithImgA:(UIImage*)imgA ImgB:(UIImage*)imgB;//设置需要对比的图片
 - (void)setImgAWidthImg:(UIImage*)img;
 - (void)setImgBWidthImg:(UIImage*)img;
 - (Similarity)getSimilarityValue; //获取相似度
 + (Similarity)getSimilarityValueWithImgA:(UIImage*)imga ImgB:(UIImage*)imgb;//类方法
 @end

GetSimilarity.m

 //
 //  GetSimilarity.m
 //  imgsimlartest
 //
 //  Created by test on 16/3/3.
 //  Copyright © 2016年 com.facishare.CoreTest. All rights reserved.
 //

 #import "GetSimilarity.h"
 #define ImgSizeA 10
 #define ImgSizeB 100
 typedef enum workday
 {
     SizeA,
     SizeB,
 }GetSimilarityType;

 @interface GetSimilarity()
 @property (nonatomic,assign) Similarity similarity;
 @property (nonatomic,strong) UIImage *imga;
 @property (nonatomic,strong) UIImage *imgb;
 @end

 @implementation GetSimilarity
 - (instancetype)init
 {
     self = [super init];
     if (self) {
         self.imga = [[UIImage alloc]init];
         self.imgb = [[UIImage alloc]init];
     }
     return self;
 }

 - (void)setImgWithImgA:(UIImage*)imgA ImgB:(UIImage*)imgB
 {
     _imga = imgA;
     _imgb = imgB;
 }

 - (void)setImgAWidthImg:(UIImage*)img
 {
     self.imga = img;
 }

 - (void)setImgBWidthImg:(UIImage*)img
 {
     self.imgb = img;
 }

 - (Similarity)getSimilarityValue
 {
     self.similarity = MAX([self getSimilarityValueWithType:SizeA], [self getSimilarityValueWithType:SizeB]);
     return self.similarity;
 }
 + (Similarity)getSimilarityValueWithImgA:(UIImage *)imga ImgB:(UIImage *)imgb
 {
     GetSimilarity * getSimilarity = [[GetSimilarity alloc]init];
     [getSimilarity setImgWithImgA:imga ImgB:imgb];
     return [getSimilarity getSimilarityValue];
 }
 - (Similarity)getSimilarityValueWithType:(GetSimilarityType)type;//
 {
     int cursize = (type == SizeA ? ImgSizeA : ImgSizeB);
     int ArrSize = cursize * cursize + ,a[ArrSize],b[ArrSize],i,j,grey,sum = ;
     CGSize size = {cursize,cursize};
     UIImage * imga = [self reSizeImage:self.imga toSize:size];
     UIImage * imgb = [self reSizeImage:self.imgb toSize:size];//缩小图片尺寸

     a[ArrSize] = ;
     b[ArrSize] = ;
     CGPoint point;
     for (i =  ; i < cursize; i++) {//计算a的灰度
         for (j = ; j < cursize; j++) {
             point.x = i;
             point.y = j;
             grey = ToGrey([self UIcolorToRGB:[self colorAtPixel:point img:imga]]);
             a[cursize * i + j] = grey;
             a[ArrSize] += grey;
         }
     }
     a[ArrSize] /= (ArrSize - );//灰度平均值
     for (i =  ; i < cursize; i++) {//计算b的灰度
         for (j = ; j < cursize; j++) {
             point.x = i;
             point.y = j;
             grey = ToGrey([self UIcolorToRGB:[self colorAtPixel:point img:imgb]]);
             b[cursize * i + j] = grey;
             b[ArrSize] += grey;
         }
     }
     b[ArrSize] /= (ArrSize - );//灰度平均值
     for (i =  ; i < ArrSize ; i++)//灰度分布计算
     {
         a[i] = (a[i] < a[ArrSize] ?  : );
         b[i] = (b[i] < b[ArrSize] ?  : );
     }
     ArrSize -= ;
     for (i =  ; i < ArrSize ; i++)
     {
         sum += (a[i] == b[i] ?  : );
     }

     return sum * 1.0 / ArrSize;
 }

 - (UIImage *)reSizeImage:(UIImage *)image toSize:(CGSize)reSize//重新设定图片尺寸
 {
     UIGraphicsBeginImageContext(CGSizeMake(reSize.width, reSize.height));
     [image drawInRect:CGRectMake(, , reSize.width, reSize.height)];
     UIImage *reSizeImage = UIGraphicsGetImageFromCurrentImageContext();
     UIGraphicsEndImageContext();
     return reSizeImage;
 }

 unsigned int ToGrey(unsigned int rgb)//RGB计算灰度
 {
     unsigned int blue   = (rgb & 0x000000FF) >> ;
     unsigned int green  = (rgb & 0x0000FF00) >> ;
     unsigned int red    = (rgb & 0x00FF0000) >> ;
     return ( red* +  green *  +  blue *  )>>;
 }

 - (unsigned int)UIcolorToRGB:(UIColor*)color//UIColor转16进制RGB
 {
     unsigned int RGB,R,G,B;
     RGB = R = G = B = 0x00000000;
     CGFloat r,g,b,a;
     [color getRed:&r green:&g blue:&b alpha:&a];
     R = r *  ;
     G = g *  ;
     B = b *  ;
     RGB = (R << ) | (G << ) | B ;
     return RGB;
 }

 - (UIColor *)colorAtPixel:(CGPoint)point img:(UIImage*)img{//获取指定point位置的RGB
     // Cancel if point is outside image coordinates
     if (!CGRectContainsPoint(CGRectMake(0.0f, 0.0f, img.size.width, img.size.height), point)) { return nil; }

     NSInteger   pointX  = trunc(point.x);
     NSInteger   pointY  = trunc(point.y);
     CGImageRef  cgImage = img.CGImage;
     NSUInteger  width   = img.size.width;
     NSUInteger  height  = img.size.height;
     int bytesPerPixel   = ;
     int bytesPerRow     = bytesPerPixel * ;
     NSUInteger bitsPerComponent = ;
     unsigned char pixelData[] = { , , ,  };
     CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
     CGContextRef context = CGBitmapContextCreate(pixelData, , , bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

     CGColorSpaceRelease(colorSpace);
     CGContextSetBlendMode(context, kCGBlendModeCopy);

     // Draw the pixel we are interested in onto the bitmap context
     CGContextTranslateCTM(context, -pointX, pointY-(CGFloat)height);
     CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, (CGFloat)width, (CGFloat)height), cgImage);
     CGContextRelease(context);
     // Convert color values [0..255] to floats [0.0..1.0]

     CGFloat red   = (CGFloat)pixelData[] / 255.0f;
     CGFloat green = (CGFloat)pixelData[] / 255.0f;
     CGFloat blue  = (CGFloat)pixelData[] / 255.0f;
     CGFloat alpha = (CGFloat)pixelData[] / 255.0f;
     return [UIColor colorWithRed:red green:green blue:blue alpha:alpha];
 }
 @end