UIImage调整大小（缩放比例）[重复]

Question

可能重复：
Resize UIImage with aspect ratio?

以下代码完美地调整了图像的大小，但问题是它弄乱了纵横比（导致图像倾斜）。有什么指点吗？

// Change image resolution (auto-resize to fit)
+ (UIImage *)scaleImage:(UIImage*)image toResolution:(int)resolution {
    CGImageRef imgRef = [image CGImage];
    CGFloat width = CGImageGetWidth(imgRef);
    CGFloat height = CGImageGetHeight(imgRef);
    CGRect bounds = CGRectMake(0, 0, width, height);

    //if already at the minimum resolution, return the orginal image, otherwise scale
    if (width <= resolution && height <= resolution) {
        return image;

    } else {
        CGFloat ratio = width/height;

        if (ratio > 1) {
            bounds.size.width = resolution;
            bounds.size.height = bounds.size.width / ratio;
        } else {
            bounds.size.height = resolution;
            bounds.size.width = bounds.size.height * ratio;
        }
    }

    UIGraphicsBeginImageContext(bounds.size);
    [image drawInRect:CGRectMake(0.0, 0.0, bounds.size.width, bounds.size.height)];
    UIImage *imageCopy = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return imageCopy;
}

Answer 1

我使用这行代码创建了一个新的 UIImage，它是缩放的。设置比例和方向参数以实现您想要的。第一行代码只是抓取图像。

    // grab the original image
    UIImage *originalImage = [UIImage imageNamed:@"myImage.png"];
    // scaling set to 2.0 makes the image 1/2 the size. 
    UIImage *scaledImage = 
                [UIImage imageWithCGImage:[originalImage CGImage] 
                              scale:(originalImage.scale * 2.0)
                                 orientation:(originalImage.imageOrientation)];

Answer 2

没关系，问题不大。问题是你必须找到成比例的宽度和高度

如果尺寸为 2048.0 x 1360.0，必须将其调整为 320 x 480 分辨率，则生成的图像尺寸应为 722.0 x 480.0

here is the formulae to do that . if w,h is original and x,y are resulting image.
w/h=x/y 
=> 
x=(w/h)*y;  

submitting w=2048,h=1360,y=480 => x=722.0 ( here width>height. if height>width then consider x to be 320 and calculate y)

你可以在这个网页上提交。 ARC

困惑？好的，这是 UIImage 的类别，它会为你做这件事。

@interface UIImage (UIImageFunctions)
    - (UIImage *) scaleToSize: (CGSize)size;
    - (UIImage *) scaleProportionalToSize: (CGSize)size;
@end
@implementation UIImage (UIImageFunctions)

- (UIImage *) scaleToSize: (CGSize)size
{
    // Scalling selected image to targeted size
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(NULL, size.width, size.height, 8, 0, colorSpace, kCGImageAlphaPremultipliedLast);
    CGContextClearRect(context, CGRectMake(0, 0, size.width, size.height));

    if(self.imageOrientation == UIImageOrientationRight)
    {
        CGContextRotateCTM(context, -M_PI_2);
        CGContextTranslateCTM(context, -size.height, 0.0f);
        CGContextDrawImage(context, CGRectMake(0, 0, size.height, size.width), self.CGImage);
    }
    else
        CGContextDrawImage(context, CGRectMake(0, 0, size.width, size.height), self.CGImage);

    CGImageRef scaledImage=CGBitmapContextCreateImage(context);

    CGColorSpaceRelease(colorSpace);
    CGContextRelease(context);

    UIImage *image = [UIImage imageWithCGImage: scaledImage];

    CGImageRelease(scaledImage);

    return image;
}

- (UIImage *) scaleProportionalToSize: (CGSize)size1
{
    if(self.size.width>self.size.height)
    {
        NSLog(@"LandScape");
        size1=CGSizeMake((self.size.width/self.size.height)*size1.height,size1.height);
    }
    else
    {
        NSLog(@"Potrait");
        size1=CGSizeMake(size1.width,(self.size.height/self.size.width)*size1.width);
    }

    return [self scaleToSize:size1];
}

@end

-- 如果 img 是 UIImage 实例，则以下是适当的调用。

img=[img scaleProportionalToSize:CGSizeMake(320, 480)];

Answer 3

这修正了将数学缩放到宽度和高度的最大尺寸，而不仅仅是一个取决于原始宽度和高度的尺寸。

- (UIImage *) scaleProportionalToSize: (CGSize)size
{
    float widthRatio = size.width/self.size.width;
    float heightRatio = size.height/self.size.height;

    if(widthRatio > heightRatio)
    {
        size=CGSizeMake(self.size.width*heightRatio,self.size.height*heightRatio);
    } else {
        size=CGSizeMake(self.size.width*widthRatio,self.size.height*widthRatio);
    }

    return [self scaleToSize:size];
}

Answer 4

这个改变对我有用：

// The size returned by CGImageGetWidth(imgRef) & CGImageGetHeight(imgRef) is incorrect as it doesn't respect the image orientation!
// CGImageRef imgRef = [image CGImage];
// CGFloat width = CGImageGetWidth(imgRef);
// CGFloat height = CGImageGetHeight(imgRef);
//
// This returns the actual width and height of the photo (and hence solves the problem
CGFloat width = image.size.width; 
CGFloat height = image.size.height;
CGRect bounds = CGRectMake(0, 0, width, height);

Answer 5

尝试将bounds 的大小设为整数。

#include <math.h>
....

    if (ratio > 1) {
        bounds.size.width = resolution;
        bounds.size.height = round(bounds.size.width / ratio);
    } else {
        bounds.size.height = resolution;
        bounds.size.width = round(bounds.size.height * ratio);
    }