IOS图片压缩和扩展

iOS自带的提供了一个API如下

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NSData *UIImageJPEGRepresentation(UIImage *image, CGFloat compressionQuality);

在Iphone上有两种读取图片数据的简单方法: UIImageJPEGRepresentation和UIImagePNGRepresentation. 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.通过在实际使用过程中,比较发现: UIImagePNGRepresentation(UIImage* image) 要比UIImageJPEGRepresentation(UIImage* image,
1.0) 返回的图片数据量大很多.譬如,同样是读取摄像头拍摄的同样景色的照片, UIImagePNGRepresentation()返回的数据量大小为199K ,而 UIImageJPEGRepresentation(UIImage* image, 1.0)返回的数据量大小只为140KB,比前者少了50多KB.如果对图片的清晰度要求不高,还可以通过设置 UIImageJPEGRepresentation函数的第二个参数,大幅度降低图片数据量.譬如,刚才拍摄的图片, 通过调用UIImageJPEGRepresentation(UIImage*
image, 1.0)读取数据时,返回的数据大小为140KB,但更改压缩系数后,通过调用UIImageJPEGRepresentation(UIImage* image, 0.5)读取数据时,返回的数据大小只有11KB多,大大压缩了图片的数据量 ,而且从视角角度看,图片的质量并没有明显的降低.因此,在读取图片数据内容时,建议优先使用UIImageJPEGRepresentation,并可根据自己的实际使用场景,设置压缩系数,进一步降低图片数据量大小。

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UIImage *imageNew = [info objectForKey:@"UIImagePickerControllerOriginalImage"];

imageNew = [self imageWithImage:imageNew scaledToSize:CGSizeMake(100, 100)];

NSData *imageData = UIImageJPEGRepresentation(imageNew, 0.0001);



m_selectImage = [UIImage imageWithData:imageData];

.h具体code



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#import <Foundation/Foundation.h>



@interface UIImage (UIImageExt)



- (UIImage *)scaleToSize:(UIImage *)img size:(CGSize)size;



- (UIImage *)imageByScalingAndCroppingForSize:(CGSize)targetSize;

@end

.m具体code

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#import "UIImageExt.h"





@implementation UIImage (UIImageExt)



- (UIImage *)scaleToSize:(UIImage *)img size:(CGSize)size{

// 创建一个bitmap的context

// 并把它设置成为当前正在使用的context

UIGraphicsBeginImageContext(size);

// 绘制改变大小的图片

[img drawInRect:CGRectMake(0, 0, size.width, size.height)];

// 从当前context中创建一个改变大小后的图片

UIImage* scaledImage = UIGraphicsGetImageFromCurrentImageContext();

// 使当前的context出堆栈

UIGraphicsEndImageContext();

// 返回新的改变大小后的图片

return scaledImage;

}







- (UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize

{

UIImage *sourceImage = self;

UIImage *newImage = nil;

CGSize imageSize = sourceImage.size;

CGFloat width = imageSize.width;

CGFloat height = imageSize.height;

CGFloat targetWidth = targetSize.width;

CGFloat targetHeight = targetSize.height;

CGFloat scaleFactor = 0.0;

CGFloat scaledWidth = targetWidth;

CGFloat scaledHeight = targetHeight;

CGPoint thumbnailPoint = CGPointMake(0.0,0.0);



if (CGSizeEqualToSize(imageSize, targetSize) == NO)

{

CGFloat widthFactor = targetWidth / width;

CGFloat heightFactor = targetHeight / height;



if (widthFactor > heightFactor)

scaleFactor = widthFactor; // scale to fit height

else

scaleFactor = heightFactor; // scale to fit width

scaledWidth = width * scaleFactor;

scaledHeight = height * scaleFactor;



// center the image

if (widthFactor > heightFactor)

{

thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;

}

else

if (widthFactor < heightFactor)

{

thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;

}

}



UIGraphicsBeginImageContext(targetSize); // this will crop



CGRect thumbnailRect = CGRectZero;

thumbnailRect.origin = thumbnailPoint;

thumbnailRect.size.width = scaledWidth;

thumbnailRect.size.height = scaledHeight;



[sourceImage drawInRect:thumbnailRect];



newImage = UIGraphicsGetImageFromCurrentImageContext();

if(newImage == nil)

NSLog(@"could not scale image");



//pop the context to get back to the default

UIGraphicsEndImageContext();

return newImage;

}



@end