UIIimage 图片的截图和压缩

- (UIImage*)scaleFromImage:(UIImage*)image scaledToSize:(CGSize)newSize
{
CGSize imageSize = image.size;
CGFloat width = imageSize.width;
CGFloat height = imageSize.height;

if (width <= newSize.width && height <= newSize.height){
return image;
}

if (width == 0 || height == 0){
return image;
}

CGFloat widthFactor = newSize.width / width;
CGFloat heightFactor = newSize.height / height;
CGFloat scaleFactor = (widthFactor<heightFactor?widthFactor:heightFactor);

CGFloat scaledWidth = width * scaleFactor;
CGFloat scaledHeight = height * scaleFactor;
CGSize targetSize = CGSizeMake(scaledWidth,scaledHeight);

UIGraphicsBeginImageContext(targetSize);
[image drawInRect:CGRectMake(0,0,scaledWidth,scaledHeight)];
UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}

//sdk中提供了方法可以直接调用

UIImage *img = [UIImage imageNamed:@"some.png"];

NSData *dataObj = UIImageJPEGRepresentation(img, 1.0);

//下面是sdk中UIImage.h头文件中的内容

UIKIT_EXTERN NSData *UIImagePNGRepresentation(UIImage *image);

// return image as PNG. May return nil if image has no CGImageRef or invalid bitmap format

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

// return image as JPEG. May return nil if image has no CGImageRef or invalid bitmap format. compression is 0(most)..1(least)

JPEG的转换方法里面第二个参数是压缩系数，可以有效的减小图片的大小。UIImagePNGRepresentation(UIImage* image) 要比UIImageJPEGRepresentation(UIImage* image, 1.0) 返回的图片数据量大很多。项目中做图片上传之前，经过测试同一张拍照所得照片png大小在8M，而JPG压缩系数为0.75时候，大小只有1M。而且，将压缩系数降低对图片视觉上并没有太大的影响。

#import <UIKit/UIKit.h>

@protocol ImageCropperDelegate;

@interface ImageCropper : UIViewController <UIScrollViewDelegate> {
UIScrollView *scrollView;
UIImageView *imageView;

id <ImageCropperDelegate> delegate;
}

@property (nonatomic, retain) UIScrollView *scrollView;
@property (nonatomic, retain) UIImageView *imageView;

@property (nonatomic, assign) id <ImageCropperDelegate> delegate;

- (id)initWithImage:(UIImage *)image;

@end

@protocol ImageCropperDelegate <NSObject>
- (void)imageCropper:(ImageCropper *)cropper didFinishCroppingWithImage:(UIImage *)image;
- (void)imageCropperDidCancel:(ImageCropper *)cropper;
@end

#import "ImageCropper.h"

@implementation ImageCropper

@synthesize scrollView, imageView;
@synthesize delegate;

- (id)initWithImage:(UIImage *)image {
self = [super init];

if (self) {
[[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleBlackTranslucent animated:YES];

scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0.0, -20.0, 320.0, 480.0)];
[scrollView setBackgroundColor:[UIColor blackColor]];
[scrollView setDelegate:self];
[scrollView setShowsHorizontalScrollIndicator:NO];
[scrollView setShowsVerticalScrollIndicator:NO];
[scrollView setMaximumZoomScale:2.0];

imageView = [[UIImageView alloc] initWithImage:image];

CGRect rect;
rect.size.width = image.size.width;
rect.size.height = image.size.height;

[imageView setFrame:rect];

[scrollView setContentSize:[imageView frame].size];
[scrollView setMinimumZoomScale:[scrollView frame].size.width / [imageView frame].size.width];
[scrollView setZoomScale:[scrollView minimumZoomScale]];
[scrollView addSubview:imageView];

[[self view] addSubview:scrollView];

UINavigationBar *navigationBar = [[UINavigationBar alloc] initWithFrame:CGRectMake(0.0, 0.0, 320.0, 44.0)];
[navigationBar setBarStyle:UIBarStyleBlack];
[navigationBar setTranslucent:YES];

UINavigationItem *aNavigationItem = [[UINavigationItem alloc] initWithTitle:@"Move and Scale"];
[aNavigationItem setLeftBarButtonItem:[[[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemCancel target:self action:@selector(cancelCropping)] autorelease]];
[aNavigationItem setRightBarButtonItem:[[[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:self action:@selector(finishCropping)] autorelease]];

[navigationBar setItems:[NSArray arrayWithObject:aNavigationItem]];

[aNavigationItem release];

[[self view] addSubview:navigationBar];

[navigationBar release];
}

return self;
}

- (void)cancelCropping {
[delegate imageCropperDidCancel:self];
}

- (void)finishCropping {
float zoomScale = 1.0 / [scrollView zoomScale];

CGRect rect;
rect.origin.x = [scrollView contentOffset].x * zoomScale;
rect.origin.y = [scrollView contentOffset].y * zoomScale;
rect.size.width = [scrollView bounds].size.width * zoomScale;
rect.size.height = [scrollView bounds].size.height * zoomScale;

CGImageRef cr = CGImageCreateWithImageInRect([[imageView image] CGImage], rect);

UIImage *cropped = [UIImage imageWithCGImage:cr];

CGImageRelease(cr);

[delegate imageCropper:self didFinishCroppingWithImage:cropped];
}

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView {
return imageView;
}

- (void)dealloc {
[imageView release];
[scrollView release];

[super dealloc];
}

@end