ios 图片处理（ 1.按比例缩放 2.指定宽度按比例缩放

-(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;

        }

    }

    UIGraphicsBeginImageContext(size);

    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;

}

//指定宽度按比例缩放

-(UIImage *) imageCompressForWidth:(UIImage *)sourceImage targetWidth:(CGFloat)defineWidth{

    UIImage *newImage = nil;

    CGSize imageSize = sourceImage.size;

    CGFloat width = imageSize.width;

    CGFloat height = imageSize.height;

    CGFloat targetWidth = defineWidth;

    CGFloat targetHeight = height / (width / targetWidth);

    CGSize size = CGSizeMake(targetWidth, targetHeight);

    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;

        }

    }

    UIGraphicsBeginImageContext(size);

    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;

}