iOS图片压缩

对于“压”功能，我们可以使用UIImageJPEGRepresentation或UIImagePNGRepresentation方法实现
第一个参数是图片对象本身，第二个参数是压的系数，其值范围为(0-1);

NSData *imgData = UIImageJPEGRepresentation(image, 0.5);

图片“缩”处理:
主要通过 [image drawInRect:CGRectMake(0, 0, targetWidth, targetHeight)]; 实现。

/**
*  1, 按图片最大边成比例缩放图片
*
*  @param image   图片
*  @param maxSize 图片的较长那一边目标缩到的(宽度／高度)
*
*  @return        等比缩放后的图片
*/
- (UIImage *)scaleImage:(UIImage *)image maxSize:(CGFloat)maxSize {
    NSData *data = UIImageJPEGRepresentation(image, 1.0);
    if(data.length < 200 * 1024){//0.25M-0.5M(当图片小于此范围不压缩)
        return image;
    }
    CGFloat imageWidth = image.size.width;
    CGFloat imageHeight = image.size.height;
    CGFloat targetWidth = imageWidth;
    CGFloat targetHeight = imageHeight;
    CGFloat imageMaxSize = MAX(imageWidth, imageHeight);
    if (imageMaxSize > maxSize) {
        CGFloat scale = 0;
        if (imageWidth >= imageHeight) {// 宽长
            scale = maxSize / imageWidth;
            targetWidth = maxSize;
            targetHeight = imageHeight * scale;
        } else { // 高长
            scale = maxSize / imageHeight;
            targetHeight = maxSize;
            targetWidth = imageWidth * scale;
        }
        UIGraphicsBeginImageContext(CGSizeMake(targetWidth, targetHeight));
        [image drawInRect:CGRectMake(0, 0, targetWidth, targetHeight)];
        UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        return scaledImage;
    }
    return image;
}

/**
*  2, 图片支持等比缩放
*
*  @param image   图片
*  @param maxSize 缩放比例(通常0～1之间)
*
*  @return        等比缩放后的图片
*/
- (UIImage *)scaleImage:(UIImage *)image toScale:(float)scaleSize {
    UIGraphicsBeginImageContext(CGSizeMake(image.size.width *scaleSize, image.size.height * scaleSize));
    [image drawInRect:CGRectMake(0, 0, image.size.width * scaleSize, image.size.height * scaleSize)];
    UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return scaledImage;
}

/**
*  3, 等比缩放成自定长宽的图片
*
*  @param image      源图片
*  @param targetSize 自定义目标图片的size
*
*  @return 处理后图片
*/
- (UIImage *)scaleImage:(UIImage *)image toSize:(CGSize)targetSize {
    UIGraphicsBeginImageContext(CGSizeMake(targetSize.width, targetSize.height));
    [image drawInRect:CGRectMake(0, 0, targetSize.width, targetSize.height)];
    UIImage *targetSizeImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return targetSizeImage;
}

//根据图片附获取图片大小(多少M)方法
- (NSData *)imageData:(UIImage *)image {
    NSData *data = UIImageJPEGRepresentation(image, 1.0);
    if (data.length > 100*1024) {
        if (data.length > 1024*1024) {//1M以及以上
            data = UIImageJPEGRepresentation(image, 0.1);
        }else if (data.length > 512*1024) {//0.5M-1M
                data = UIImageJPEGRepresentation(image, 0.5);
        }else if (data.length > 200*1024) {//0.25M-0.5M
            data = UIImageJPEGRepresentation(image, 0.9);
        }
    }
    return data;
}

原图大小为24.9M, 4288 * 2848像素；经一次UIImageJPEGRepresentation“压“处理

UIImage *tmpImage = [UIImage imageWithContentsOfFile:photo.photoPath];NSData *imageData = UIImageJPEGRepresentation(tmpImage, 0.5);

图片大小为836.9K, 4288 * 2848像素；
经一次UIImagePNGRepresentation“压“处理

UIImage *tmpImage = [UIImage imageWithContentsOfFile:photo.photoPath];NSData *imageData = UIImagePNGRepresentation(tmpImage);

图片大小为24.9M, 4288 * 2848像素；几乎没变
经一次“缩“处理(笔者给予图片最大的宽度限定为640像素)

UIImage *tmpImage = [UIImage imageWithContentsOfFile:photo.photoPath];tmpImage = [self scaleImage:tmpImage maxSize:640];

图片大小为795.9K, 640 * 426像素；
经一次“压缩”处理:

UIImage *tmpImage = [UIImage imageWithContentsOfFile:photo.photoPath];tmpImage = [self scaleImage:tmpImage maxSize:640];NSData *imageData = UIImageJPEGRepresentation(tmpImage, 0.5);

图片大小为698K, 640 * 426像素；大家可以根据实际调整不同参数以达到自己的项目要求。