如何缩放图像？

Question

如何缩放高质量的图像。我正在使用以下代码，但是当我使用相机中的图像时，它会显示在不同的帧中。

-(UIImage *)resizeImage:(UIImage *)image {
int w = image.size.width;
int h = image.size.height; 

CGImageRef imageRef = [image CGImage];

int width, height;

int destWidth = 640;
int destHeight = 480;
if(w > h){
    width = destWidth;
    height = h*destWidth/w;
} else {
    height = destHeight;
    width = w*destHeight/h;
}

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

CGContextRef bitmap;
bitmap = CGBitmapContextCreate(NULL, width, height, 8, 4 * width, colorSpace, kCGImageAlphaPremultipliedFirst);

if (image.imageOrientation == UIImageOrientationLeft) {
    CGContextRotateCTM (bitmap, M_PI/2);
    CGContextTranslateCTM (bitmap, 0, -height);

} else if (image.imageOrientation == UIImageOrientationRight) {
    CGContextRotateCTM (bitmap, -M_PI/2);
    CGContextTranslateCTM (bitmap, -width, 0);

} else if (image.imageOrientation == UIImageOrientationUp) {

} else if (image.imageOrientation == UIImageOrientationDown) {
    CGContextTranslateCTM (bitmap, width,height);
    CGContextRotateCTM (bitmap, -M_PI);

}

CGContextDrawImage(bitmap, CGRectMake(0, 0, width, height), imageRef);
CGImageRef ref = CGBitmapContextCreateImage(bitmap);
UIImage *result = [UIImage imageWithCGImage:ref];

CGContextRelease(bitmap);
CGImageRelease(ref);

return result;  
}

如果有什么办法可以在不影响质量的情况下缩小尺寸，请建议 提前致谢

Answer 1

为了减小尺寸，您将不得不在图像的分辨率上做出妥协。我建议你为图像计算一个新的 WIDTH 和 HEIGHT。

这对我有用：

试试这个：

-(UIImage*) resizeImage:(CGImageRef)image toWidth:(int)width andHeight:(int)height
{
// create context, keeping original image properties
  CGColorSpaceRef colorspace = CGImageGetColorSpace(image);
  CGContextRef context = CGBitmapContextCreate(NULL, width, height,                                                 CGImageGetBitsPerComponent(image),                                           CGImageGetBytesPerRow(image),
                                             colorspace,
                                             CGImageGetAlphaInfo(image));

       if(context == NULL)
       {
        NSLog(@"Could not re-size");
        return nil; 
       }
      // draw image to context (resizing it)
      CGContextDrawImage(context, CGRectMake(0, 0, width, height), image);
      // extract resulting image from context
      CGImageRef imgRef = CGBitmapContextCreateImage(context);
      CGContextRelease(context);
      UIImage* resizedImage = [UIImage imageWithCGImage:imgRef];
      CGImageRelease(imgRef);
      return resizedImage;  
}

Answer 2

我使用下面的代码来缩放相机图像的图像。如果您觉得有帮助，请实施

- (void)imagePickerController:(UIImagePickerController *)picker
                didFinishPickingImage:(UIImage *)image
                                    editingInfo:(NSDictionary *)editingInfo
{

//// ADDIGN THIS LINE WHEN YOU CAPTURED IMAGE 

    image = [self scaleAndRotateImage:image];
    [self useImage:image];
    [[picker parentViewController] dismissModalViewControllerAnimated:YES];
}

/// THE METHODS ROTATE THE CURRENT CAPTURED IMAGE AT 90 DEGREE OF ANGLE

- (void)scaleAndRotateImage:(UIImage *)image
{
    int kMaxResolution = 320; // Or whatever

    CGImageRef imgRef = image.CGImage;

    CGFloat width = CGImageGetWidth(imgRef);
    CGFloat height = CGImageGetHeight(imgRef);

    CGAffineTransform transform = CGAffineTransformIdentity;
    CGRect bounds = CGRectMake(0, 0, width, height);
    if (width > kMaxResolution || height > kMaxResolution) {
        CGFloat ratio = width/height;
        if (ratio > 1) {
            bounds.size.width = kMaxResolution;
            bounds.size.height = bounds.size.width / ratio;
        }
        else {
            bounds.size.height = kMaxResolution;
            bounds.size.width = bounds.size.height * ratio;
        }
    }

    CGFloat scaleRatio = bounds.size.width / width;
    CGSize imageSize = CGSizeMake(CGImageGetWidth(imgRef), CGImageGetHeight(imgRef));
    CGFloat boundHeight;
    UIImageOrientation orient = image.imageOrientation;
    switch(orient) {

        case UIImageOrientationUp: //EXIF = 1
            transform = CGAffineTransformIdentity;
            break;

        case UIImageOrientationUpMirrored: //EXIF = 2
            transform = CGAffineTransformMakeTranslation(imageSize.width, 0.0);
            transform = CGAffineTransformScale(transform, -1.0, 1.0);
            break;

        case UIImageOrientationDown: //EXIF = 3
            transform = CGAffineTransformMakeTranslation(imageSize.width, imageSize.height);
            transform = CGAffineTransformRotate(transform, M_PI);
            break;

        case UIImageOrientationDownMirrored: //EXIF = 4
            transform = CGAffineTransformMakeTranslation(0.0, imageSize.height);
            transform = CGAffineTransformScale(transform, 1.0, -1.0);
            break;

        case UIImageOrientationLeftMirrored: //EXIF = 5
            boundHeight = bounds.size.height;
            bounds.size.height = bounds.size.width;
            bounds.size.width = boundHeight;
            transform = CGAffineTransformMakeTranslation(imageSize.height, imageSize.width);
            transform = CGAffineTransformScale(transform, -1.0, 1.0);
            transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);
            break;

        case UIImageOrientationLeft: //EXIF = 6
            boundHeight = bounds.size.height;
            bounds.size.height = bounds.size.width;
            bounds.size.width = boundHeight;
            transform = CGAffineTransformMakeTranslation(0.0, imageSize.width);
            transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);
            break;

        case UIImageOrientationRightMirrored: //EXIF = 7
            boundHeight = bounds.size.height;
            bounds.size.height = bounds.size.width;
            bounds.size.width = boundHeight;
            transform = CGAffineTransformMakeScale(-1.0, 1.0);
            transform = CGAffineTransformRotate(transform, M_PI / 2.0);
            break;

        case UIImageOrientationRight: //EXIF = 8
            boundHeight = bounds.size.height;
            bounds.size.height = bounds.size.width;
            bounds.size.width = boundHeight;
            transform = CGAffineTransformMakeTranslation(imageSize.height, 0.0);
            transform = CGAffineTransformRotate(transform, M_PI / 2.0);
            break;

        default:
            [NSException raise:NSInternalInconsistencyException format:@"Invalid image orientation"];

    }

    UIGraphicsBeginImageContext(bounds.size);

    CGContextRef context = UIGraphicsGetCurrentContext();

    if (orient == UIImageOrientationRight || orient == UIImageOrientationLeft) {
        CGContextScaleCTM(context, -scaleRatio, scaleRatio);
        CGContextTranslateCTM(context, -height, 0);
    }
    else {
        CGContextScaleCTM(context, scaleRatio, -scaleRatio);
        CGContextTranslateCTM(context, 0, -height);
    }

    CGContextConcatCTM(context, transform);

    CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, width, height), imgRef);
    UIImage *imageCopy = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    [self setRotatedImage:imageCopy];
    //return imageCopy;
}