ios中图像进行压缩方法汇总

方法一：

- (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;
}

方法二：

.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 

方法三：（本人项目中使用的方法）

-(uiimage *) imagecompressforwidth:(uiimage *)sourceimage targetwidth:(cgfloat)definewidth
{
    cgsize imagesize = sourceimage.size;
    cgfloat width = imagesize.width;
    cgfloat height = imagesize.height;
    cgfloat targetwidth = definewidth;
    cgfloat targetheight = (targetwidth / width) * height;
    uigraphicsbeginimagecontext(cgsizemake(targetwidth, targetheight));
    [sourceimage drawinrect:cgrectmake(0,0,targetwidth,  targetheight)];
    uiimage* newimage = uigraphicsgetimagefromcurrentimagecontext();
    uigraphicsendimagecontext();
    return newimage;
}

以上所述就是本文的全部内容了，希望大家能够喜欢。