这几天我一直在用自己的脸来抨击这个问题，尽管我一直觉得我正处于启示的边缘，但我根本无法实现我的目标。
我认为，在我的设计的概念阶段提前，从 iPhone 的相机或库中抓取图像，将其缩小到指定的高度，使用相当于 Aspect Fill 选项（完全在代码中），然后裁剪任何不适合传递的 CGRect 的内容。
从相机或库中获取原始图像是微不足道的。我对其他两个步骤的难度如此之大感到震惊。
所附图片显示了我想要实现的目标。有人会好心地握住我的手吗？到目前为止，我发现的每个代码示例似乎都会破坏图像、上下颠倒、看起来像废话、绘制越界或无法正常工作。
【问题讨论】：
标签： iphone ios image-processing core-graphics
我发现 Evgenii Kanvets 发布的 Swift 3 并没有统一缩放图像。
这是我的 Swift 4 版本的不挤压图像的函数：
static func resizedCroppedImage(image: UIImage, newSize:CGSize) -> UIImage? {
// This function returns a newImage, based on image
// - image is scaled uniformaly to fit into a rect of size newSize
// - if the newSize rect is of a different aspect ratio from the source image
// the new image is cropped to be in the center of the source image
// (the excess source image is removed)
var ratio: CGFloat = 0
var delta: CGFloat = 0
var drawRect = CGRect()
if newSize.width > newSize.height {
ratio = newSize.width / image.size.width
delta = (ratio * image.size.height) - newSize.height
drawRect = CGRect(x: 0, y: -delta / 2, width: newSize.width, height: newSize.height + delta)
} else {
ratio = newSize.height / image.size.height
delta = (ratio * image.size.width) - newSize.width
drawRect = CGRect(x: -delta / 2, y: 0, width: newSize.width + delta, height: newSize.height)
}
UIGraphicsBeginImageContextWithOptions(newSize, true, 0.0)
image.draw(in: drawRect)
let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return newImage
}
【讨论】：
UIGraphicsBeginImageContextWithOptions 中将缩放比例设置为 1.0，但其他的效果很好。谢谢！
这是由 William T 发布的 Sam Wirch's guide to swift 的 Swift 3 版本。
extension UIImage {
static func resizedCroppedImage(image: UIImage, newSize:CGSize) -> UIImage? {
var ratio: CGFloat = 0
var delta: CGFloat = 0
var offset = CGPoint.zero
if image.size.width > image.size.height {
ratio = newSize.width / image.size.width
delta = (ratio * image.size.width) - (ratio * image.size.height)
offset = CGPoint(x: delta / 2, y: 0)
} else {
ratio = newSize.width / image.size.height
delta = (ratio * image.size.height) - (ratio * image.size.width)
offset = CGPoint(x: 0, y: delta / 2)
}
let clipRect = CGRect(x: -offset.x, y: -offset.y, width: (ratio * image.size.width) + delta, height: (ratio * image.size.height) + delta)
UIGraphicsBeginImageContextWithOptions(newSize, true, 0.0)
UIRectClip(clipRect)
image.draw(in: clipRect)
let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return newImage
}
}
【讨论】：
这是 Jane Sales 在 Swift 中的答案的一个版本。干杯!
public func resizeImage(image: UIImage, size: CGSize) -> UIImage? {
var returnImage: UIImage?
var scaleFactor: CGFloat = 1.0
var scaledWidth = size.width
var scaledHeight = size.height
var thumbnailPoint = CGPointMake(0, 0)
if !CGSizeEqualToSize(image.size, size) {
let widthFactor = size.width / image.size.width
let heightFactor = size.height / image.size.height
if widthFactor > heightFactor {
scaleFactor = widthFactor
} else {
scaleFactor = heightFactor
}
scaledWidth = image.size.width * scaleFactor
scaledHeight = image.size.height * scaleFactor
if widthFactor > heightFactor {
thumbnailPoint.y = (size.height - scaledHeight) * 0.5
} else if widthFactor < heightFactor {
thumbnailPoint.x = (size.width - scaledWidth) * 0.5
}
}
UIGraphicsBeginImageContextWithOptions(size, true, 0)
var thumbnailRect = CGRectZero
thumbnailRect.origin = thumbnailPoint
thumbnailRect.size.width = scaledWidth
thumbnailRect.size.height = scaledHeight
image.drawInRect(thumbnailRect)
returnImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return returnImage
}
【讨论】：
Swift 版本：
static func imageWithImage(image:UIImage, newSize:CGSize) ->UIImage {
UIGraphicsBeginImageContextWithOptions(newSize, true, UIScreen.mainScreen().scale);
image.drawInRect(CGRectMake(0, 0, newSize.width, newSize.height))
let newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage
}
【讨论】：
我转换了Sam Wirch's guide to swift，它对我来说效果很好，尽管最终图像中有一些我无法解决的非常轻微的“挤压”。
func resizedCroppedImage(image: UIImage, newSize:CGSize) -> UIImage {
var ratio: CGFloat = 0
var delta: CGFloat = 0
var offset = CGPointZero
if image.size.width > image.size.height {
ratio = newSize.width / image.size.width
delta = (ratio * image.size.width) - (ratio * image.size.height)
offset = CGPointMake(delta / 2, 0)
} else {
ratio = newSize.width / image.size.height
delta = (ratio * image.size.height) - (ratio * image.size.width)
offset = CGPointMake(0, delta / 2)
}
let clipRect = CGRectMake(-offset.x, -offset.y, (ratio * image.size.width) + delta, (ratio * image.size.height) + delta)
UIGraphicsBeginImageContextWithOptions(newSize, true, 0.0)
UIRectClip(clipRect)
image.drawInRect(clipRect)
let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return newImage
}
如果有人想要客观的 c 版本，在他的网站上。
【讨论】：
这个问题似乎已经解决了，但是在我寻求一个我可以更容易理解（并用 Swift 编写）的解决方案时，我想到了这个（也发布到：How to crop the UIImage?）
我希望能够根据纵横比从区域裁剪，并根据外部边界范围缩放到大小。这是我的变体：
import AVFoundation
import ImageIO
class Image {
class func crop(image:UIImage, crop source:CGRect, aspect:CGSize, outputExtent:CGSize) -> UIImage {
let sourceRect = AVMakeRectWithAspectRatioInsideRect(aspect, source)
let targetRect = AVMakeRectWithAspectRatioInsideRect(aspect, CGRect(origin: CGPointZero, size: outputExtent))
let opaque = true, deviceScale:CGFloat = 0.0 // use scale of device's main screen
UIGraphicsBeginImageContextWithOptions(targetRect.size, opaque, deviceScale)
let scale = max(
targetRect.size.width / sourceRect.size.width,
targetRect.size.height / sourceRect.size.height)
let drawRect = CGRect(origin: -sourceRect.origin * scale, size: image.size * scale)
image.drawInRect(drawRect)
let scaledImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return scaledImage
}
}
有几件事让我感到困惑，裁剪和调整大小的不同问题。裁剪由您传递给 drawInRect 的矩形的原点处理，缩放由大小部分处理。就我而言，我需要将源上的裁剪矩形的大小与相同纵横比的输出矩形相关联。然后输出/输入比例因子，这需要应用于drawRect（传递给drawInRect）。
需要注意的是，这种方法有效地假设您正在绘制的图像大于图像上下文。我没有对此进行测试，但我认为您可以使用此代码来处理裁剪/缩放，但将比例参数明确定义为上述比例参数。默认情况下，UIKit 根据屏幕分辨率应用乘数。
最后，应该注意的是，这种 UIKit 方法比 CoreGraphics / Quartz 和 Core Image 方法级别更高，并且似乎可以处理图像方向问题。还值得一提的是，它非常快，仅次于 ImageIO，根据这里的这篇文章：http://nshipster.com/image-resizing/
【讨论】：
- (UIImage*)imageScale:(CGFloat)scaleFactor cropForSize:(CGSize)targetSize
{
targetSize = !targetSize.width?self.size:targetSize;
UIGraphicsBeginImageContext(targetSize); // this will crop
CGRect thumbnailRect = CGRectZero;
thumbnailRect.size.width = targetSize.width*scaleFactor;
thumbnailRect.size.height = targetSize.height*scaleFactor;
CGFloat xOffset = (targetSize.width- thumbnailRect.size.width)/2;
CGFloat yOffset = (targetSize.height- thumbnailRect.size.height)/2;
thumbnailRect.origin = CGPointMake(xOffset,yOffset);
[self drawInRect:thumbnailRect];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
if(newImage == nil)
{
NSLog(@"could not scale image");
}
UIGraphicsEndImageContext();
return newImage;
}
下面的工作示例： 左图 - （原图） ;比例为 x2 的右图
如果你想缩放图像但保留它的框架（比例），这样调用方法：
[yourImage imageScale:2.0f cropForSize:CGSizeZero];
【讨论】：
accepted answer on how to resize and then crop UIImage (Aspect Fill) 的 Xamarin.iOS 版本是 下面
public static UIImage ScaleAndCropImage(UIImage sourceImage, SizeF targetSize)
{
var imageSize = sourceImage.Size;
UIImage newImage = null;
var width = imageSize.Width;
var height = imageSize.Height;
var targetWidth = targetSize.Width;
var targetHeight = targetSize.Height;
var scaleFactor = 0.0f;
var scaledWidth = targetWidth;
var scaledHeight = targetHeight;
var thumbnailPoint = PointF.Empty;
if (imageSize != targetSize)
{
var widthFactor = targetWidth / width;
var heightFactor = targetHeight / height;
if (widthFactor > heightFactor)
{
scaleFactor = widthFactor;// scale to fit height
}
else
{
scaleFactor = heightFactor;// scale to fit width
}
scaledWidth = width * scaleFactor;
scaledHeight = height * scaleFactor;
// center the image
if (widthFactor > heightFactor)
{
thumbnailPoint.Y = (targetHeight - scaledHeight) * 0.5f;
}
else
{
if (widthFactor < heightFactor)
{
thumbnailPoint.X = (targetWidth - scaledWidth) * 0.5f;
}
}
}
UIGraphics.BeginImageContextWithOptions(targetSize, false, 0.0f);
var thumbnailRect = new RectangleF(thumbnailPoint, new SizeF(scaledWidth, scaledHeight));
sourceImage.Draw(thumbnailRect);
newImage = UIGraphics.GetImageFromCurrentImageContext();
if (newImage == null)
{
Console.WriteLine("could not scale image");
}
//pop the context to get back to the default
UIGraphics.EndImageContext();
return newImage;
}
【讨论】：
较早的帖子包含调整 UIImage 大小的方法的代码。相关部分如下：
+ (UIImage*)imageWithImage:(UIImage*)image
scaledToSize:(CGSize)newSize;
{
UIGraphicsBeginImageContext( newSize );
[image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
就裁剪而言，我相信如果您更改方法以使用与上下文不同的大小进行缩放，则生成的图像应该被裁剪到上下文的范围内。
【讨论】：
originalImage 中没有返回正确的方向。谢谢。
UIGraphicsBeginImageContextWithOptions(newSize, 1.0f, 0.0f);。 （此处解释：stackoverflow.com/questions/4334233/…）
给你。这个是完美的;-)
编辑：见下面的评论 - “不适用于某些图像，失败：CGContextSetInterpolationQuality: invalid context 0x0 error”
// Resizes the image according to the given content mode, taking into account the image's orientation
- (UIImage *)resizedImageWithContentMode:(UIViewContentMode)contentMode imageToScale:(UIImage*)imageToScale bounds:(CGSize)bounds interpolationQuality:(CGInterpolationQuality)quality {
//Get the size we want to scale it to
CGFloat horizontalRatio = bounds.width / imageToScale.size.width;
CGFloat verticalRatio = bounds.height / imageToScale.size.height;
CGFloat ratio;
switch (contentMode) {
case UIViewContentModeScaleAspectFill:
ratio = MAX(horizontalRatio, verticalRatio);
break;
case UIViewContentModeScaleAspectFit:
ratio = MIN(horizontalRatio, verticalRatio);
break;
default:
[NSException raise:NSInvalidArgumentException format:@"Unsupported content mode: %d", contentMode];
}
//...and here it is
CGSize newSize = CGSizeMake(imageToScale.size.width * ratio, imageToScale.size.height * ratio);
//start scaling it
CGRect newRect = CGRectIntegral(CGRectMake(0, 0, newSize.width, newSize.height));
CGImageRef imageRef = imageToScale.CGImage;
CGContextRef bitmap = CGBitmapContextCreate(NULL,
newRect.size.width,
newRect.size.height,
CGImageGetBitsPerComponent(imageRef),
0,
CGImageGetColorSpace(imageRef),
CGImageGetBitmapInfo(imageRef));
CGContextSetInterpolationQuality(bitmap, quality);
// Draw into the context; this scales the image
CGContextDrawImage(bitmap, newRect, imageRef);
// Get the resized image from the context and a UIImage
CGImageRef newImageRef = CGBitmapContextCreateImage(bitmap);
UIImage *newImage = [UIImage imageWithCGImage:newImageRef];
// Clean up
CGContextRelease(bitmap);
CGImageRelease(newImageRef);
return newImage;
}
【讨论】：
scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0.0,0.0,ScreenWidth,ScreenHeigth)];
[scrollView setBackgroundColor:[UIColor blackColor]];
[scrollView setDelegate:self];
[scrollView setShowsHorizontalScrollIndicator:NO];
[scrollView setShowsVerticalScrollIndicator:NO];
[scrollView setMaximumZoomScale:2.0];
image=[image scaleToSize:CGSizeMake(ScreenWidth, ScreenHeigth)];
imageView = [[UIImageView alloc] initWithImage:image];
UIImageView* imageViewBk = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"background.png"]];
[self.view addSubview:imageViewBk];
CGRect rect;
rect.origin.x=0;
rect.origin.y=0;
rect.size.width = image.size.width;
rect.size.height = image.size.height;
[imageView setFrame:rect];
[scrollView setContentSize:[imageView frame].size];
[scrollView setMinimumZoomScale:[scrollView frame].size.width / [imageView frame].size.width];
[scrollView setZoomScale:[scrollView minimumZoomScale]];
[scrollView addSubview:imageView];
[[self view] addSubview:scrollView];
然后你可以通过这个截图到你的图像
float zoomScale = 1.0 / [scrollView zoomScale];
CGRect rect;
rect.origin.x = [scrollView contentOffset].x * zoomScale;
rect.origin.y = [scrollView contentOffset].y * zoomScale;
rect.size.width = [scrollView bounds].size.width * zoomScale;
rect.size.height = [scrollView bounds].size.height * zoomScale;
CGImageRef cr = CGImageCreateWithImageInRect([[imageView image] CGImage], rect);
UIImage *cropped = [UIImage imageWithCGImage:cr];
CGImageRelease(cr);
【讨论】：
我需要同样的东西 - 在我的例子中，选择适合缩放后的尺寸，然后裁剪每一端以适应其余部分的宽度。 （我在横向工作，所以可能没有注意到纵向模式的任何缺陷。）这是我的代码 - 它是 UIImage 类别的一部分。我的代码中的目标尺寸始终设置为设备的全屏尺寸。
@implementation UIImage (Extras)
#pragma mark -
#pragma mark Scale and crop image
- (UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize
{
UIImage *sourceImage = self;
UIImage *newImage = nil;
CGSize imageSize = sourceImage.size;
CGFloat width = imageSize.width;
CGFloat height = imageSize.height;
CGFloat targetWidth = targetSize.width;
CGFloat targetHeight = targetSize.height;
CGFloat scaleFactor = 0.0;
CGFloat scaledWidth = targetWidth;
CGFloat scaledHeight = targetHeight;
CGPoint thumbnailPoint = CGPointMake(0.0,0.0);
if (CGSizeEqualToSize(imageSize, targetSize) == NO)
{
CGFloat widthFactor = targetWidth / width;
CGFloat heightFactor = targetHeight / height;
if (widthFactor > heightFactor)
{
scaleFactor = widthFactor; // scale to fit height
}
else
{
scaleFactor = heightFactor; // scale to fit width
}
scaledWidth = width * scaleFactor;
scaledHeight = height * scaleFactor;
// center the image
if (widthFactor > heightFactor)
{
thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;
}
else
{
if (widthFactor < heightFactor)
{
thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
}
}
}
UIGraphicsBeginImageContext(targetSize); // this will crop
CGRect thumbnailRect = CGRectZero;
thumbnailRect.origin = thumbnailPoint;
thumbnailRect.size.width = scaledWidth;
thumbnailRect.size.height = scaledHeight;
[sourceImage drawInRect:thumbnailRect];
newImage = UIGraphicsGetImageFromCurrentImageContext();
if(newImage == nil)
{
NSLog(@"could not scale image");
}
//pop the context to get back to the default
UIGraphicsEndImageContext();
return newImage;
}
【讨论】：
以下简单代码对我有用。
[imageView setContentMode:UIViewContentModeScaleAspectFill];
[imageView setClipsToBounds:YES];
【讨论】：
UIImageView 对象。然而，这个问题是关于缩放UIImage 对象本身。
我修改了 Brad Larson 的代码。它将在给定的矩形中填充图像。
-(UIImage*) scaleAndCropToSize:(CGSize)newSize;
{
float ratio = self.size.width / self.size.height;
UIGraphicsBeginImageContext(newSize);
if (ratio > 1) {
CGFloat newWidth = ratio * newSize.width;
CGFloat newHeight = newSize.height;
CGFloat leftMargin = (newWidth - newHeight) / 2;
[self drawInRect:CGRectMake(-leftMargin, 0, newWidth, newHeight)];
}
else {
CGFloat newWidth = newSize.width;
CGFloat newHeight = newSize.height / ratio;
CGFloat topMargin = (newHeight - newWidth) / 2;
[self drawInRect:CGRectMake(0, -topMargin, newSize.width, newSize.height/ratio)];
}
UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
【讨论】：
+ (UIImage *)scaleImage:(UIImage *)image toSize:(CGSize)targetSize {
//If scaleFactor is not touched, no scaling will occur
CGFloat scaleFactor = 1.0;
//Deciding which factor to use to scale the image (factor = targetSize / imageSize)
if (image.size.width > targetSize.width || image.size.height > targetSize.height)
if (!((scaleFactor = (targetSize.width / image.size.width)) > (targetSize.height / image.size.height))) //scale to fit width, or
scaleFactor = targetSize.height / image.size.height; // scale to fit heigth.
UIGraphicsBeginImageContext(targetSize);
//Creating the rect where the scaled image is drawn in
CGRect rect = CGRectMake((targetSize.width - image.size.width * scaleFactor) / 2,
(targetSize.height - image.size.height * scaleFactor) / 2,
image.size.width * scaleFactor, image.size.height * scaleFactor);
//Draw the image into the rect
[image drawInRect:rect];
//Saving the image, ending image context
UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return scaledImage;
}
我建议这个。她不是美女吗？ ;)
【讨论】：
有一段很棒的代码与调整图像大小和其他几个操作有关。当我试图弄清楚如何调整图像大小时，我遇到了这个问题...... http://vocaro.com/trevor/blog/2009/10/12/resize-a-uiimage-the-right-way/
【讨论】：