一，截圖一般需要用到兩大功能：全屏截圖和指定區(qū)域截圖桃移。
二屋匕，拿到一些圖片，需要對(duì)圖片進(jìn)行合成的時(shí)候借杰，外層圖片的底色會(huì)很討厭过吻，我們需要把那層討厭的顏色去掉，換成透明的蔗衡，或者指定的某種顏色纤虽。比如我們代碼生成的二維碼圖片，默認(rèn)出來(lái)就是白色底绞惦，但是將該二維碼和展示公司形象的圖片組合的時(shí)候逼纸，那張白色底在很顯眼，最好是給換成透明的济蝉。

全屏截圖需要考慮的是當(dāng)前界面是否有導(dǎo)航欄杰刽，指定區(qū)域截圖需要考慮的是當(dāng)前手機(jī)屏幕對(duì)圖片的縮放比例。
修改圖片的顏色王滤，其實(shí)是遍歷該image的每個(gè)像素點(diǎn)贺嫂，然后找到對(duì)應(yīng)的ARGB進(jìn)行值替換。

/**
 *  將圖片中的指定顏色轉(zhuǎn)換為透明
 */
- (UIImage *)imageToTransparentWithOriginalColor:(UIColor *)originalColor {
    // 分解原來(lái)的顏色
    CGFloat red = 0.0;
    CGFloat green = 0.0;
    CGFloat blue = 0.0;
    CGFloat alpha = 0.0;
    [originalColor getRed:&red green:&green blue:&blue alpha:&alpha];
    
    // 分配內(nèi)存
    const int imageWidth = self.size.width;
    const int imageHeight = self.size.height;
    size_t bytesPerRow = imageWidth * 4;
    uint32_t *rgbImageBuf = (uint32_t *)malloc(bytesPerRow * imageHeight);
    
    // 創(chuàng)建context
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(rgbImageBuf, imageWidth, imageHeight, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast);
    CGContextDrawImage(context, CGRectMake(0, 0, imageWidth, imageHeight), self.CGImage);
    
    // 遍歷像素
    int pixelNum = imageWidth * imageHeight;
    uint32_t* pCurPtr = rgbImageBuf;
    for (int i = 0; i < pixelNum; i++, pCurPtr++) {
        //將像素點(diǎn)轉(zhuǎn)成子節(jié)數(shù)組來(lái)表示---第一個(gè)表示透明度即ARGB這種表示方式雁乡。ptr[0]:透明度,ptr[1]:R,ptr[2]:G,ptr[3]:B
        //分別取出RGB值后第喳。進(jìn)行判斷需不需要設(shè)成透明。
        uint8_t* ptr = (uint8_t *)pCurPtr;
        // NSLog(@"1是%d,2是%d,3是%d",ptr[1],ptr[2],ptr[3]);
        if(ptr[1] == red * 255 || ptr[2] == green * 255 || ptr[3] == blue * 255) {
            ptr[0] = 0;
        }
    }
    
    // 將內(nèi)存轉(zhuǎn)成image
    CGDataProviderRef dataProvider =CGDataProviderCreateWithData(NULL, rgbImageBuf, bytesPerRow * imageHeight, nil);
    CGImageRef imageRef = CGImageCreate(imageWidth, imageHeight,8, 32, bytesPerRow, colorSpace, kCGImageAlphaLast |kCGBitmapByteOrder32Little, dataProvider, NULL, true,kCGRenderingIntentDefault);
    CGDataProviderRelease(dataProvider);
    UIImage* resultUIImage = [UIImage imageWithCGImage:imageRef];
    
    // 釋放
    CGImageRelease(imageRef);
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);
    
    return resultUIImage;
}
/**
 *  將圖片中的指定顏色轉(zhuǎn)換為新的顏色
 *
 *  @pram originalColor 原來(lái)的顏色
 *  @pram newColor      新的顏色
 */
- (UIImage *)imageOriginalColor:(UIColor *)originalColor toNewColor:(UIColor *)newColor {
    // 分解原來(lái)的顏色
    CGFloat red1 = 0.0;
    CGFloat green1 = 0.0;
    CGFloat blue1 = 0.0;
    CGFloat alpha1 = 0.0;
    CGFloat red2 = 0.0;
    CGFloat green2 = 0.0;
    CGFloat blue2 = 0.0;
    CGFloat alpha2 = 0.0;
    [originalColor getRed:&red1 green:&green1 blue:&blue1 alpha:&alpha1];
    [newColor getRed:&red2 green:&green2 blue:&blue2 alpha:&alpha2];
    
    // 分配內(nèi)存
    const int imageWidth = self.size.width;
    const int imageHeight = self.size.height;
    size_t bytesPerRow = imageWidth * 4;
    uint32_t *rgbImageBuf = (uint32_t *)malloc(bytesPerRow * imageHeight);
    
    // 創(chuàng)建context
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(rgbImageBuf, imageWidth, imageHeight, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast);
    CGContextDrawImage(context, CGRectMake(0, 0, imageWidth, imageHeight), self.CGImage);
    
    // 遍歷像素
    int pixelNum = imageWidth * imageHeight;
    uint32_t* pCurPtr = rgbImageBuf;
    for (int i = 0; i < pixelNum; i++, pCurPtr++) {
        // 將像素點(diǎn)轉(zhuǎn)成子節(jié)數(shù)組來(lái)表示---第一個(gè)表示透明度即ARGB這種表示方式蔗怠。
        // ptr[0]:透明度,ptr[1]:R,ptr[2]:G,ptr[3]:B
        uint8_t* ptr = (uint8_t *)pCurPtr;
        if (ptr[0] == alpha1) ptr[0] = alpha2;
        if (ptr[1] == red1 * 255) ptr[1] = red2 * 255;
        if (ptr[2] == green1 * 255) ptr[2] = green2 * 255;
        if (ptr[3] == blue1 * 255) ptr[3] = blue2 * 255;
    }
    
    // 將內(nèi)存轉(zhuǎn)成image
    CGDataProviderRef dataProvider =CGDataProviderCreateWithData(NULL, rgbImageBuf, bytesPerRow * imageHeight, nil);
    CGImageRef imageRef = CGImageCreate(imageWidth, imageHeight,8, 32, bytesPerRow, colorSpace, kCGImageAlphaLast |kCGBitmapByteOrder32Little, dataProvider, NULL, true,kCGRenderingIntentDefault);
    CGDataProviderRelease(dataProvider);
    UIImage* resultUIImage = [UIImage imageWithCGImage:imageRef];
    
    // 釋放
    CGImageRelease(imageRef);
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);
    
    return resultUIImage;
}
/**
 *  全屏截圖
 */
+ (UIImage *)screenShot {
    return  [self screenShotWithRect:[UIApplication sharedApplication].keyWindow.bounds isNavigation:NO];
}
/**
 *  屏幕截圖
 *
 *  @pram rect         截圖的frame
 *  @pram isNavigation 導(dǎo)航欄是否顯示
 */
+ (UIImage *)screenShotWithRect:(CGRect)rect isNavigation:(BOOL)isNavigation {
    // 獲取屏幕放大比例
    CGFloat scale = [UIScreen mainScreen].scale;
    CGRect newRect = rect;
    newRect.size.width *= scale;
    newRect.size.height *= scale;
    CGFloat height = 0;
    if (isNavigation) {
        height = NavigationViewHeight;
    }
    newRect.origin.y += height;
    newRect.origin.x *= scale;
    newRect.origin.y *= scale;
    // 設(shè)置截屏大小
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(newRect.size.width, newRect.size.height), YES, 0);
    [[UIApplication sharedApplication].keyWindow.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    CGImageRef imageRef = viewImage.CGImage;
    // 設(shè)置截圖的區(qū)域
    CGImageRef imageRefRect = CGImageCreateWithImageInRect(imageRef, newRect);
    UIImage *sendImage = [[UIImage alloc] initWithCGImage:imageRefRect];
    // 保存圖片到照片庫(kù)
    //    UIImageWriteToSavedPhotosAlbum(sendImage, nil, nil, nil);
    return sendImage;
}
/**
 *  返回截取到的圖片數(shù)據(jù)類型
 */
+ (NSData *)dataWithScreenshot {
    UIImage *image = [self imageWithScreenshot];
    UIGraphicsEndImageContext();
    return UIImagePNGRepresentation(image);
}
/**
 *  截取當(dāng)前屏幕
 */
+ (UIImage *)imageWithScreenshot {
    CGSize imageSize = CGSizeZero;
    UIInterfaceOrientation orientation = [UIApplication sharedApplication].statusBarOrientation;
    if (UIInterfaceOrientationIsPortrait(orientation))
        imageSize = [UIScreen mainScreen].bounds.size;
    else
        imageSize = CGSizeMake([UIScreen mainScreen].bounds.size.height, [UIScreen mainScreen].bounds.size.width);
    UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    for (UIWindow *window in [[UIApplication sharedApplication] windows]) {
        CGContextSaveGState(context);
        CGContextTranslateCTM(context, window.center.x, window.center.y);
        CGContextConcatCTM(context, window.transform);
        CGContextTranslateCTM(context, -window.bounds.size.width * window.layer.anchorPoint.x, -window.bounds.size.height * window.layer.anchorPoint.y);
        if (orientation == UIInterfaceOrientationLandscapeLeft) {
            CGContextRotateCTM(context, M_PI_2);
            CGContextTranslateCTM(context, 0, -imageSize.width);
        } else if (orientation == UIInterfaceOrientationLandscapeRight) {
            CGContextRotateCTM(context, -M_PI_2);
            CGContextTranslateCTM(context, -imageSize.height, 0);
        } else if (orientation == UIInterfaceOrientationPortraitUpsideDown) {
            CGContextRotateCTM(context, M_PI);
            CGContextTranslateCTM(context, -imageSize.width, -imageSize.height);
        }
        if ([window respondsToSelector:@selector(drawViewHierarchyInRect:afterScreenUpdates:)]) {
            [window drawViewHierarchyInRect:window.bounds afterScreenUpdates:YES];
        } else {
            [window.layer renderInContext:context];
        }
        CGContextRestoreGState(context);
    }
    return UIGraphicsGetImageFromCurrentImageContext();
}