iOS图片缩略图生成-优快云博客

- (UIImage *)thumbnailWithImageWithoutScale:(UIImage *)image size:(CGSize)asize
{
    UIImage *newimage;
    if (nil == image) {
        newimage = nil;
    }
    else{
        CGSize oldsize = image.size;
        CGRect rect;
        if (asize.width/asize.height > oldsize.width/oldsize.height) {
            rect.size.width = asize.height*oldsize.width/oldsize.height;
            rect.size.height = asize.height;
            rect.origin.x = (asize.width - rect.size.width)/2;
            rect.origin.y = 0;
        }
        else{
            rect.size.width = asize.width;
            rect.size.height = asize.width*oldsize.height/oldsize.width;
            rect.origin.x = 0;
            rect.origin.y = (asize.height - rect.size.height)/2;
        }
        UIGraphicsBeginImageContext(asize);
        CGContextRef context = UIGraphicsGetCurrentContext();
        CGContextSetFillColorWithColor(context, [[UIColor clearColor] CGColor]);
        UIRectFill(CGRectMake(0, 0, asize.width, asize.height));//clear background
        [image drawInRect:rect];
        newimage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
    }
    return newimage;
}
- (UIImage *)generatePhotoThumbnail:(UIImage *)image {
    // Create a thumbnail version of the image for the event object.
    CGSize size = image.size;
    CGSize croppedSize;
    CGFloat ratio = 4.0;
    CGFloat offsetX = 0.0;
    CGFloat offsetY = 0.0;

    // check the size of the image, we want to make it
    // a square with sides the size of the smallest dimension
    if (size.width > size.height) {
        offsetX = (size.height - size.width) / 2;
        croppedSize = CGSizeMake(size.height, size.height);
    } else {
        offsetY = (size.width - size.height) / 2;
        croppedSize = CGSizeMake(size.width, size.width);
    }

    // Crop the image before resize
    CGRect clippedRect = CGRectMake(offsetX * -1, offsetY * -1, croppedSize.width, croppedSize.height);
    CGImageRef imageRef = CGImageCreateWithImageInRect([image CGImage], clippedRect);
    // Done cropping

    // Resize the image
    CGRect rect = CGRectMake(0.0, 0.0, ratio, ratio);

    UIGraphicsBeginImageContext(rect.size);
    [[UIImage imageWithCGImage:imageRef] drawInRect:rect];
    UIImage *thumbnail = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    // Done Resizing

    return thumbnail;
}
-(UIImage *)imageCompressForSize:(UIImage *)sourceImage targetSize:(CGSize)size{

    UIImage *newImage = nil;

    CGSize imageSize = sourceImage.size;

    CGFloat width = imageSize.width;

    CGFloat height = imageSize.height;

    CGFloat targetWidth = size.width;

    CGFloat targetHeight = size.height;

    CGFloat scaleFactor = 0.0;

    CGFloat scaledWidth = targetWidth;

    CGFloat scaledHeight = targetHeight;

    CGPoint thumbnailPoint = CGPointMake(0.0, 0.0);

    if(CGSizeEqualToSize(imageSize, size) == NO){

        CGFloat widthFactor = targetWidth / width;

        CGFloat heightFactor = targetHeight / height;

        if(widthFactor > heightFactor){

            scaleFactor = widthFactor;

        }

        else{

            scaleFactor = heightFactor;

        }

        scaledWidth = width * scaleFactor;

        scaledHeight = height * scaleFactor;

        if(widthFactor > heightFactor){

            thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;

        }else if(widthFactor < heightFactor){

            thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;

        }

    }

    UIGraphicsBeginImageContextWithOptions(size, NO, 3.0);

    CGRect thumbnailRect = CGRectZero;

    thumbnailRect.origin = thumbnailPoint;

    thumbnailRect.size.width = scaledWidth;

    thumbnailRect.size.height = scaledHeight;

    [sourceImage drawInRect:thumbnailRect];

    newImage = UIGraphicsGetImageFromCurrentImageContext();

    if(newImage == nil){

        NSLog(@"scale image fail");

    }

    UIGraphicsEndImageContext();

    return newImage;

}