UIImage 和 iOS 图片压缩UIImage / UIImageVIew

UIImageView

制作气泡

stretchableImageWithLeftCapWidth

http://blog.csdn.net/justinjing0612/article/details/8751269

1.图片缓存

使用第三方库: SDWebImage

 UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 200, 200)];
 [imageView setImageWithURL:[NSURL URLWithString:@"http://img.taobaocdn.com/bao/uploaded/TB1UXkgGpXXXXcDXVXXSutbFXXX.jpg"]];
 [self.view addSubview:imageView];

这样可以实现异步下载, 图片缓存,从过缓存在离线状态下访问图片

2. iOS 图片压缩UIImage

经本人测试:

NSData *data1 = UIImagePNGRepresentation(image);

NSData *data2 = UIImageJPEGRepresentation(image, 1);

NSData *data = UIImageJPEGRepresentation(image, 0.5);

使用以上这三种图片压缩方法, 分别得到了326kb, 121kb, 19kb的图片大小, 

图片质量肉眼比较难分辨出来, 但是图片大小相差甚远, 所以一般我们采用第三种, 这里图片质量我定为0.5, 大家可以根据需求在(0 ~ 1)随意改动这个数值 

3269470,1212494,192836

iOS自带的提供了一个API如下

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。

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

#import <Foundation/Foundation.h>

@interface UIImage (UIImageExt)

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

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

.m具体code

#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