ios - 在不影响 objective-c 质量的情况下缩小图像

Question

如何在不影响质量的情况下以编程方式缩小图像。

捕获图像后，我想在不改变 objective-c 质量的情况下减小该图像的大小。

Answer 1

这是我用来压缩图片的代码

代码:

-(UIImage *)compressImage:(UIImage *)image{

    NSData *imgData = UIImageJPEGRepresentation(image, 1); //1 it represents the quality of the image.
    NSLog(@"Size of Image(bytes):%ld",(unsigned long)[imgData length]);

    float actualHeight = image.size.height;
    float actualWidth = image.size.width;
    float maxHeight = 600.0;
    float maxWidth = 800.0;
    float imgRatio = actualWidth/actualHeight;
    float maxRatio = maxWidth/maxHeight;
    float compressionQuality = 0.5;//50 percent compression

    if (actualHeight > maxHeight || actualWidth > maxWidth){
        if(imgRatio < maxRatio){
            //adjust width according to maxHeight
            imgRatio = maxHeight / actualHeight;
            actualWidth = imgRatio * actualWidth;
            actualHeight = maxHeight;
        }
        else if(imgRatio > maxRatio){
            //adjust height according to maxWidth
            imgRatio = maxWidth / actualWidth;
            actualHeight = imgRatio * actualHeight;
            actualWidth = maxWidth;
        }
        else{
            actualHeight = maxHeight;
            actualWidth = maxWidth;
        }
    }

    CGRect rect = CGRectMake(0.0, 0.0, actualWidth, actualHeight);
    UIGraphicsBeginImageContext(rect.size);
    [image drawInRect:rect];
    UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
    NSData *imageData = UIImageJPEGRepresentation(img, compressionQuality);
    UIGraphicsEndImageContext();

    NSLog(@"Size of Image(bytes):%ld",(unsigned long)[imageData length]);

    return [UIImage imageWithData:imageData];
}

所以这是使用上面的代码

UIImage *org = [UIImage imageNamed:@"MacLehose Stage 7 Stunning Natural Sceneries.jpg"];

UIImage *imgCompressed = [self compressImage:org];

如果要压缩更多

NSData *dataImage = UIImageJPEGRepresentation(imgCompressed, 0.0);

NSLog(@"Size of Image(bytes):%ld",(unsigned long)[dataImage length]);

通过上述方式，我能够将图像从 2 MB 压缩到接近 50 KB。