本节实现效果:在图片内嵌入文字实现验证码;
核心知识: 提取图片指定区域主色调;
重要说明:代码中所涉及的坐标均基于图片实际像素尺寸坐标,并非UIImageView的尺寸坐标;
实现步骤:
1.获取图片指定区域主要色彩;
2.在图片指定位置绘制文字做旋转.模糊.变形等处理;
一.效果如下:
图一:图片色调跳跃较大的情况
图二:图片色调较平滑的情况
图三:图片色调平滑的情况
可以明显的看出:
1.在图一的中文字过于明显,容易被提取特征点后分析识别;
2.在图二中局部区域比较理想,对于较明亮处依然存在图一的问题;
3.在图三中整体效果尚且可以,但是文字太暗,用户体验较差;
针对以上问题,其实都是图片本身过于明亮所致,故在重新绘制图片是选择- (void)drawInRect:(CGRect)rect blendMode:(CGBlendMode)blendMode alpha:(CGFloat)alpha方法,手动调节图片透明度即可,甚至可以给图片覆盖特定的前景色;
当然,既然获取了文字所在区域的像素值,人为制造噪点也是可以的!!!
二.获取图片指定区域主要色彩
主要代码如下:
-(UIColor*)mostColor:(UIImage*)image atRegion:(CGRect)region{
CGImageRef inImage = 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];//该方法下文会讲解
if (cgctx == NULL) {
return nil; /* error */
}
size_t w = CGImageGetWidth(inImage);
size_t h = CGImageGetHeight(inImage);
CGRect rect = {{0,0},{w,h}};
// 绘制
CGContextDrawImage(cgctx, rect, inImage);
// Now we can get a pointer to the image data associated with the bitmap
// 对应像素点从左向右 Z 字型保存,所在在获取特定点时 offset = (w*y)+x
unsigned char* data = (unsigned char*)CGBitmapContextGetData(cgctx);
NSCountedSet *cls=[NSCountedSet setWithCapacity:region.size.width*region.size.height];
// 获取坐标 x,y 处的像素点颜色值 ARGB
for (NSInteger x = region.origin.x ; x<region.origin.x + region.size.width ; x++) {
for (NSInteger y = region.origin.y; y< region.origin.y + region.size.height; y++) {
NSInteger offset = 4*((w*y)+x); //对应像素点从左向右 Z 字型保存
if (offset + 4 >= w*h*4) {
break;
}
NSInteger alpha = data[offset];
NSInteger red = data[offset + 1] ;
NSInteger green = data[offset+2];
NSInteger blue = data[offset+3];
[cls addObject:@[@(red),@(green),@(blue),@(alpha)]];
}
}
CGContextRelease(cgctx);
if (data) { free(data); }
// 找到出现次数最多的那个颜色
NSEnumerator *enumerator = [cls objectEnumerator];
NSArray *curColor = nil;
NSArray *MaxColor = nil;
NSUInteger MaxCount=0;
while ( (curColor = [enumerator nextObject])){
NSUInteger tmpCount = [cls countForObject:curColor];
if ( tmpCount < MaxCount ) continue;
MaxCount = tmpCount;
MaxColor = curColor;
}
return [UIColor colorWithRed:([MaxColor[0] intValue]/255.0f) green:([MaxColor[1] intValue]/255.0f) blue:([MaxColor[2] intValue]/255.0f) alpha:1.f/*([MaxColor[3] intValue]/255.0f)*/];
}
上述代码没什么特别的地方,提一句NSCountedSet, NSCountedSet继承自NSSet,意味着NSCountedSet也不能存储相同的元素,但是,这个但是很及时,当NSCountedSet添加相同的元素时,会维护一个计数器,记录当前元素添加的次数,随后可以调用 countForObject获取对应元素存储次数;
CGImageRef 到 CGContextRef转换:
- (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;
}
三.在图片指定位置绘制文字做旋转.模糊.变形等处理
-(UIImage *)drawTitles:(NSArray<NSString *> *)titles regions:(NSArray<NSString *> *)rects onImage:(UIImage *)sourceImage{
//原始image的宽高
CGFloat viewWidth = sourceImage.size.width;
CGFloat viewHeight = sourceImage.size.height;
//为了防止图片失真，绘制区域宽高和原始图片宽高一样
UIGraphicsBeginImageContext(CGSizeMake(viewWidth, viewHeight));
// [[UIColor lightGrayColor] setFill];
// UIRectFill(CGRectMake(0, 0, viewWidth, viewHeight));
//先将原始image绘制上
[sourceImage drawInRect:CGRectMake(0, 0, viewWidth, viewHeight) blendMode:kCGBlendModeOverlay alpha:0.9f];
// [sourceImage drawInRect:CGRectMake(0, 0, viewWidth, viewHeight)];
//旋转上下文矩阵，绘制文字
CGContextRef context = UIGraphicsGetCurrentContext();
for (int i = 0; i < titles.count; i++) {
NSString *title = titles[i];
// 文字所在位置
CGRect region = CGRectFromString(rects[i]);
// 主色调
UIColor *mostColor = [self mostColor:sourceImage atRegion:region];
// 随机旋转角
CGFloat ratation = (M_PI / (rand() % 10 ));
// 不建议随机处理阴影,避免大概率出现文字无法显示问题
NSShadow *shadow = [[NSShadow alloc] init];
shadow.shadowBlurRadius = 5;
shadow.shadowColor = mostColor;
shadow.shadowOffset = CGSizeMake(3 ,4);
// 添加文本颜色和阴影等效果
NSDictionary *attr = @{
//设置字体大小,可自行随机
NSFontAttributeName: [UIFont systemFontOfSize:100],
//设置文字颜色
NSForegroundColorAttributeName :mostColor,
NSShadowAttributeName:shadow,
NSVerticalGlyphFormAttributeName:@(0),
};
NSMutableAttributedString *attrStr = [[NSMutableAttributedString alloc] initWithString:title attributes:attr];
//将绘制原点（0，0）调整到源文字的中心
CGContextConcatCTM(context, CGAffineTransformMakeTranslation(region.origin.x + region.size.width / 2.f, region.origin.y + region.size.height / 2.f));
// 以源文字的中心为中心旋转
CGContextConcatCTM(context, CGAffineTransformMakeRotation(ratation));
// 将绘制原点恢复初始值，保证当前context中心和源image的中心处在一个点(当前context已经旋转，所以绘制出的任何layer都是倾斜的)
CGContextConcatCTM(context, CGAffineTransformMakeTranslation(-region.origin.x - region.size.width / 2.f, -region.origin.y -region.size.height / 2.f));
// 绘制源文字
[title drawInRect:CGRectMake(region.origin.x , region.origin.y, attrStr.size.width, attrStr.size.height) withAttributes:attr];
}
UIImage *finalImg = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
CGContextRestoreGState(context);
return finalImg;
}
注释已经很详细了,不做赘述,直接看一个例子:
特别注意:
1.- (void)drawInRect:(CGRect)rect blendMode:(CGBlendMode)blendMode alpha:(CGFloat)alpha方法;
2.所有坐标均是基于图片本身像素尺寸,并非UIIMageView;
本例中所用图片 image.size 为:800*800,
注意需要保证rectN 的x+width < image.size.width 并且 y+height < image.size. height才可正确绘制,实际可根据自身情况对rectN采用合适的方式随机生成;
// 按照图片尺寸随机即可
NSString *rect1 = NSStringFromCGRect(CGRectMake(100, 350, 100, 100));
NSString *rect2 = NSStringFromCGRect(CGRectMake(200, 400, 100, 100));
NSString *rect3 = NSStringFromCGRect(CGRectMake(350, 200, 100, 100));
NSString *rect4 = NSStringFromCGRect(CGRectMake(550, 300, 100, 100));
self.filterImageView.image = [self drawTitles:@[@"测",@"试",@"字",@"体"]
regions:@[rect1,rect2,rect3,rect4]
onImage:self.originalImageView.image];
