1.图片的压缩
1、是 “压” 文件体积变小，但是像素数不变，长宽尺寸不变，那么质量可能下降
2、是 “缩” 文件的尺寸变小，也就是像素数减少。长宽尺寸变小，文件体积同样会减小。
这个 UIImageJPEGRepresentation(image, 0.0)，是1的功能。
这个 [sourceImage drawInRect:CGRectMake(0,0,targetWidth, targetHeight)] 是2的功能。
* UIImageJPEGRepresentation函数需要两个参数:图片的引用和压缩系数而UIImagePNGRepresentation只需要图片引用作为参数.
* UIImagePNGRepresentation(UIImage *image)要比UIImageJPEGRepresentation(UIImage* image, 1.0)返回的图片数据量大很多.
- (UIImage *)compressImage:(UIImage *)sourceImage toTargetWidth:(CGFloat)targetWidth {
CGSize imageSize = sourceImage.size;
CGFloat width = imageSize.width;
CGFloat height = imageSize.height;
CGFloat targetHeight = (targetWidth / width) * height;
UIGraphicsBeginImageContext(CGSizeMake(targetWidth, targetHeight));
[sourceImage drawInRect:CGRectMake(0, 0, targetWidth, targetHeight)];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
截图
//获得屏幕图像
- (UIImage *)imageFromView: (UIView *) theView
{
UIGraphicsBeginImageContext(theView.frame.size);
CGContextRef context = UIGraphicsGetCurrentContext();
[theView.layer renderInContext:context];
UIImage *theImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return theImage;
}
//获得某个范围内的屏幕图像
- (UIImage *)imageFromView:(UIView *)theView atFrame:(CGRect)r
{
UIGraphicsBeginImageContext(theView.frame.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSaveGState(context);
UIRectClip(r);
[theView.layer renderInContext:context];
UIImage *theImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return theImage;
}
一个区分 PNG 、JPG 格式的判断方法, 取出图片数据的第一个字节, 就可以判断出图片的真实类型:
//通过图片Data数据第一个字节 来获取图片扩展名
- (NSString *)contentTypeForImageData:(NSData *)data {
uint8_t c;
[data getBytes:&c length:1];
switch (c) {
case 0xFF:
return @"jpeg";
case 0x89:
return @"png";
case 0x47:
return @"gif";
case 0x49:
case 0x4D:
return @"tiff";
case 0x52:
if ([data length] < 12) {
return nil;
}
NSString *testString = [[NSString alloc] initWithData:[data subdataWithRange:NSMakeRange(0, 12)] encoding:NSASCIIStringEncoding];
if ([testString hasPrefix:@"RIFF"] && [testString hasSuffix:@"WEBP"]) {
return @"webp";
}
return nil;
}
return nil;
}
截取圆形图片
/**
* parm:sourceImage:需要剪切的原图片
* parm:borderWidth:剪切后的边框宽度
* parm:borderColor:边框颜色
*/
- (UIImage *)circleImageWithImage:(UIImage *)sourceImage borderWidth:(CGFloat)borderWidth borderColor:(UIColor *)borderColor{
CGFloat imageWidth = sourceImage.size.width + 2 * borderWidth;
CGFloat imageHeight = sourceImage.size.height + 2 * borderWidth;
UIGraphicsBeginImageContextWithOptions(CGSizeMake(imageWidth, imageHeight), NO, 0.0);
UIGraphicsGetCurrentContext();
CGFloat radius = (sourceImage.size.width < sourceImage.size.height?sourceImage.size.width:sourceImage.size.height)*0.5;
UIBezierPath *bezierPath = [UIBezierPath bezierPathWithArcCenter:CGPointMake(imageWidth * 0.5, imageHeight * 0.5) radius:radius startAngle:0 endAngle:M_PI * 2 clockwise:YES];
bezierPath.lineWidth = borderWidth;
[borderColor setStroke];
[bezierPath stroke];
[bezierPath addClip];
[sourceImage drawInRect:CGRectMake(borderWidth, borderWidth, sourceImage.size.width, sourceImage.size.height)];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
