动态获取图片色值，黑点坐标

如图：点击或者根据图中黑点滑动获取图片色值及黑点坐标。ColorImageView是继承UIImageView的封装，用起来很方便。

下面我们先讲demo的ViewController布局：

1，引进ColorImageView.h ；

#import "ColorImageView.h"

2, 声明了两个label用于显示rag值 及黑点位置；

@interface ViewController ()
@property (nonatomic,strong)UILabel *rgbLabel;//rgba
@property (nonatomic,strong)UILabel *locationLabel;//黑点位置
@end

3, 就是把声明的label在 viewDidLoad 中进行添加：

_rgbLabel = [[UILabel alloc] init];
_rgbLabel.frame=CGRectMake(10,60, self.view.frame.size.width-20, 23);
_rgbLabel.backgroundColor = [UIColor clearColor];
_rgbLabel.font = [UIFont systemFontOfSize:13 ];
_rgbLabel.textAlignment = NSTextAlignmentCenter;
_rgbLabel.textColor = [UIColor blackColor];
_rgbLabel.text = @"点击或移动下面的彩色图片，获取色值！";
[self.view addSubview:_rgbLabel];

_locationLabel = [[UILabel alloc] init];
_locationLabel.frame=CGRectMake(10,90, self.view.frame.size.width-20, 23);
_locationLabel.backgroundColor = [UIColor clearColor];
_locationLabel.font = [UIFont systemFontOfSize:13 ];
_locationLabel.textAlignment = NSTextAlignmentCenter;
_locationLabel.textColor = [UIColor whiteColor];
[self.view addSubview:_locationLabel];

4，把封装的ColorImageView也添加在viewDidLoad中，关于ColorImageView值传出我用的是一个block，如果对block不理解，就自己上网查咯！

ColorImageView *colorImageView = [[ColorImageView alloc] initWithFrame:CGRectMake((self.view.frame.size.width-248)/2,130, 248, 248)];
colorImageView.backgroundColor = [UIColor clearColor];
colorImageView.userInteractionEnabled = YES;
colorImageView.image = [UIImage imageNamed:@"color_s"];
//避免循序引用 弱化
__weak typeof(self) weakSelf = self;
colorImageView.block =^ (NSString *rgbaString,NSString *locationString,UIColor *color){
weakSelf.rgbLabel.text = rgbaString;
weakSelf.rgbLabel.textColor = color;
weakSelf.locationLabel.text = locationString;
};
[self.view addSubview:colorImageView];

上面ViewController的介绍完了，下面就是（重头戏）ColorImageView的封装介绍：

1，开始就是控件的添加 ，有注释 ；不用多说直接粘代码：

//
//ColorImageVIew.m
//  TableView_choose
//
//  Created by Simon on 16/6/15.
//  Copyright © 2016年 Simon. All rights reserved.
//
#import "ColorImageView.h"
#define radiusColor  120 //图片半径值
@interface ColorImageView ()
@property (nonatomic,strong)UIImageView *selectColorIamge;//黑点
@property (nonatomic,copy)NSString *rgbaString;//rgb字符串
@property (nonatomic,copy)NSString *locationString;//黑点位置字符串
@end
@implementation ColorImageView
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
// Initialization code
_selectColorIamge = [[UIImageView alloc] init];
_selectColorIamge.backgroundColor = [UIColor blackColor];
_selectColorIamge.frame=CGRectMake((frame.size.width-16)/2, (frame.size.height-16)/2, 16, 16);
_selectColorIamge.layer.cornerRadius = 8;
_selectColorIamge.layer.masksToBounds = YES;
[self addSubview:_sel
4000
ectColorIamge];

}
return self;
}

2，用系统自带touchesBegan touchesMoved touchesEnded方法实现我们的点击，移动；在移动中要限制黑点不能逃出色值图片的范围，就有了一个关于高中数学的运算，挺有意思的（不妨看看，是不是很多人都忘了）！这里block的传值就是这一句_block(_rgbaString,_locationString,color);

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch* touch = [touches anyObject];
CGPoint point = [touch locationInView:self]; //where image was tapped
CGPoint center = CGPointMake(self.frame.size.width/2, self.frame.size.height/2);
float distance = [self distanceFromPointX:center distanceToPointY:point];
if(distance<radiusColor){
_selectColorIamge.center =point;
dispatch_async(dispatch_get_main_queue(), ^{
UIColor* color = [self getPixelColorAtLocation:point];
if (_block) {
_block(_rgbaString,_locationString,color);
}
});
}
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch* touch = [touches anyObject];
CGPoint point = [touch locationInView:self]; //where image was tapped
CGPoint center = CGPointMake(self.frame.size.width/2, self.frame.size.height/2);
float distance = [self distanceFromPointX:center distanceToPointY:point];
if(distance<radiusColor){
_selectColorIamge.center =point;
dispatch_async(dispatch_get_main_queue(), ^{
UIColor* color = [self getPixelColorAtLocation:point];
if (_block) {
_block(_rgbaString,_locationString,color);
}
});
}else{
double xx=powf(point.x-radiusColor,2);
double yy=powf(point.y-radiusColor,2);
double xy=xx+yy;//圆心到手指停留处的距离(平方)
double poingXy=sqrtf(xy);//圆心到手指停留处的距离(直线）
double Geometric = (radiusColor-1)/poingXy;//等比值
double groundx=(point.x-radiusColor)*Geometric+radiusColor;//圆边x坐标
double groundy=(point.y-radiusColor)*Geometric+radiusColor;//圆边y坐标
CGPoint groundByoed = CGPointMake(groundx, groundy);
_selectColorIamge.center =groundByoed;
dispatch_async(dispatch_get_main_queue(), ^{
UIColor* color = [self getPixelColorAtLocation:point];
if (_block) {
_block(_rgbaString,_locationString,color);
}
});
}
}
- (void) touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event {
UITouch* touch = [touches anyObject];
CGPoint point = [touch locationInView:self]; //
CGPoint center = CGPointMake(self.frame.size.width/2, self.frame.size.height/2);
float distance = [self distanceFromPointX:center distanceToPointY:point];
if(distance<radiusColor){
_selectColorIamge.center =point;
dispatch_async(dispatch_get_main_queue(), ^{
UIColor* color = [self getPixelColorAtLocation:point];
if (_block) {
_block(_rgbaString,_locationString,color);
}
});
}
}

3，上面看到（distanceFromPointX：distanceToPointY：）一直都有调用，他是干什么的呢；其实很简单，就是把黑点限制在牢里用的（不逃出色值图片范围）：

//计算圆点所在位置
-(float)distanceFromPointX:(CGPoint)start distanceToPointY:(CGPoint)end{
float distance;
//下面就是高中的数学，不详细解释了
CGFloat xDist = (end.x - start.x);
CGFloat yDist = (end.y - start.y);
distance = sqrt((xDist * xDist) + (yDist * yDist));
return distance;
}

4，（getPixelColorAtLocation：）和（createARGBBitmapContextFromImage：）这两个方法呢，就是关键所在了，把在色值图片上黑点的位置转化成我们想要的值。。不明白的多看看，实在不行就找度娘！

#pragma mark private
- (UIColor*)getPixelColorAtLocation:(CGPoint)point {
UIColor* color = nil;
CGImageRef inImage = self.image.CGImage;
// Create off screen bitmap context to draw the image into. Format ARGB is 4 bytes for each pixel: Alpa, Red, Green, Blue
CGContextRef cgctx = [self createARGBBitmapContextFromImage:inImage];
if (cgctx == NULL) { return nil; /* error */ }
size_t w = CGImageGetWidth(inImage);
size_t h = CGImageGetHeight(inImage);
CGRect rect = {{0,0},{w,h}};
// Draw the image to the bitmap context. Once we draw, the memory
// allocated for the context for rendering will then contain the
// raw image data in the specified color space.
CGContextDrawImage(cgctx, rect, inImage);
if(rect.size.width==480){
point.x = point.x*2;
point.y = point.y*2;
}
// Now we can get a pointer to the image data associated with the bitmap
// context.
unsigned char* data = CGBitmapContextGetData (cgctx);
if (data != NULL) {
//读取RGB颜色值
//offset locates the pixel in the data from x,y.
//4 for 4 bytes of data per pixel, w is width of one row of data.
int offset = 4*((w*round(point.y))+round(point.x));
int alpha =  data[offset];
unsigned int red = data[offset+1];
unsigned int green = data[offset+2];
unsigned int blue = data[offset+3];
color = [UIColor colorWithRed:(red/255.0f) green:(green/255.0f) blue:(blue/255.0f) alpha:(alpha/255.0f)];
_rgbaString = [NSString stringWithFormat:@"RGBA值： red:%d  green:%d  blue:%d  alpha:%d",red,green,blue,alpha];
_locationString =[NSString stringWithFormat:@"黑点位置point： %.2f  %.2f",point.x,point.y];
}
// When finished, release the context
CGContextRelease(cgctx);
// Free image data memory for the context
if (data) {
free(data);
}
return color;
}

- (CGContextRef)createARGBBitmapContextFromImage:(CGImageRef) inImage {
CGContextRef    context = NULL;
CGColorSpaceRef colorSpace;
void *          bitmapData;
long             bitmapByteCount;
long             bitmapBytesPerRow;

// Get image width, height. We'll use the entire image.
size_t pixelsWide = CGImageGetWidth(inImage);
size_t pixelsHigh = CGImageGetHeight(inImage);
// Declare the number of bytes per row. Each pixel in the bitmap in this
// example is represented by 4 bytes; 8 bits each of red, green, blue, and
// alpha.
bitmapBytesPerRow   = (pixelsWide * 4);
bitmapByteCount     = (bitmapBytesPerRow * pixelsHigh);
// Use the generic RGB color space.
colorSpace = CGColorSpaceCreateDeviceRGB();
if (colorSpace == NULL)
{
fprintf(stderr, "Error allocating color space\n");
return NULL;
}
// Allocate memory for image data. This is the destination in memory
// where any drawing to the bitmap context will be rendered.
bitmapData = malloc( bitmapByteCount );
if (bitmapData == NULL)
{
fprintf (stderr, "Memory not allocated!");
CGColorSpaceRelease( colorSpace );
return NULL;
}
// Create the bitmap context. We want pre-multiplied ARGB, 8-bits
// per component. Regardless of what the source image format is
// (CMYK, Grayscale, and so on) it will be converted over to the format
// specified here by CGBitmapContextCreate.
context = CGBitmapContextCreate (bitmapData,
pixelsWide,
pixelsHigh,
8,      // bits per component
bitmapBytesPerRow,
colorSpace,
kCGImageAlphaPremultipliedFirst);
if (context == NULL)
{
free (bitmapData);
//fprintf (stderr, "Context not created!");
}
// Make sure and release colorspace before returning
CGColorSpaceRelease( colorSpace );
return context；
}