iOS：使用叠加层裁剪从UIImagePickerController摄像头抓取的静止图像 [英] iOS: Cropping a still image grabbed from a UIImagePickerController camera with overlay
问题描述
我是iOS的新手，过去一周我在网上寻找这样的教程，例如：处理Exif图像，调整图像大小，以及StackOverflow上的更多随机问题。从这些，我认为> = iOS 4.0 ，从相机拍摄的所有图像都包含基于 EXIF 的旋转信息。
I am new to iOS and I have been bashing head against the wall for this for the past week looking around online for tutorials such as: Dealing with Exif Images, Resizing images, and many more random questions here on StackOverflow. From these, I figured that >=iOS 4.0, all images taken from the camera contain EXIF-based rotation information.
什么不起作用：尝试不同的图像裁剪技术后，我最终得到的就是在一些随机角落裁剪图像，生成的图像似乎放大了:(当我从互联网上使用 png 图像（不包含EXIF数据）时，裁剪工作正常。 ，我的意思是 - 图像最终被裁剪在右上角/左上角并放大。
What's not working: After trying different image cropping techniques, all I end up with is cropping of the image at some random corners and also, the resulting image appears to be zoomed in :( When I use a png image from the internet (which don't contain EXIF data), the cropping is working. By random corners, I mean - the image ends up being cropped at the top-right/top-left and zoomed-in.
我想要实现的目标：
我正在尝试从顶部裁剪图像 100 px 并且 100 px 从底部开始。基本上，我使用两个叠加条 - 顶部为1，底部为1， CGRect（0.0,0.0，SCREEN_WIDTH，100.0） [a 100.0 px 顶部的高条带]和另一个 CGRect（0.0，SCREEN_HEIGHT - 100，SCREEN _WIDTH，100.0） [另一个 100 px 底部的高条]。我需要在这两个条带之间获取图像：我假设图像的高度为： SCREEN_HEIGHT - 200.0 。
What I am trying to accomplish:
I am trying to crop an image 100 px from top and 100 px from bottom. Essentially, I am using two overlay strips - 1 at the top, and 1 at the bottom with the CGRect(0.0, 0.0, SCREEN_WIDTH, 100.0) [a 100.0 px tall strip at the top] and another CGRect(0.0, SCREEN_HEIGHT - 100, SCREEN_WIDTH, 100.0) [another 100 px tall strip at the bottom]. I need to get the image between these two strips: I assume the height of the image is: SCREEN_HEIGHT - 200.0.
显示覆盖相机的UIImagePickerController：
//SCREEN_HEIGHT = 480 and SCREEN_WIDTH = 320
UIImagePickerController *imagePicker = [[UIImagePickerController alloc] init];
if([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera] == NO)
{
NSLog(@"Camera not available");
return;
}
imagePicker.sourceType = UIImagePickerControllerSourceTypeCamera;
imagePicker.delegate = self;
imagePicker.allowsEditing = NO;
// Hide the controls
imagePicker.showsCameraControls = NO;
imagePicker.navigationBarHidden = YES;
// Make camera view full screen
imagePicker.wantsFullScreenLayout = YES;
//imagePicker.cameraViewTransform = CGAffineTransformScale(imagePicker.cameraViewTransform, CAMERA_TRANSFORM_X, CAMERA_TRANSFORM_Y);
//Overlay
//OverlayView is a plain UIView with the CGRects mentioned in the question.
OverlayView *overlay = [[OverlayView alloc] initWithFrame:CGRectMake(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT)];
[overlay initOverlay:self];
imagePicker.cameraOverlayView = overlay;
[self presentModalViewController:imagePicker animated:YES];
基于EXIF旋转图像的代码 imageOrientation 属性并裁剪
Code to rotate image based on EXIF imageOrientation property and cropping it
- (UIImage *) cropImage: (UIImage *) originalImage
{
CGRect cropRect = CGRectMake(0, 100.0, SCREEN_WIDTH, SCREEN_HEIGHT - 100);
CGRect transformedRect = [self TransformCGRectForUIImageOrientation:cropRect :originalImage.imageOrientation :originalImage.size];
CGImageRef resultImageRef = CGImageCreateWithImageInRect(originalImage.CGImage, transformedRect);
UIImage *newImage = [[[UIImage alloc] initWithCGImage:resultImageRef scale:1.0 orientation:originalImage.imageOrientation] autorelease];
return newImage;
}
- (CGRect) TransformCGRectForUIImageOrientation: (CGRect) source: (UIImageOrientation) orientation: (CGSize) imageSize {
switch (orientation) {
case UIImageOrientationLeft: { // EXIF #8
CGAffineTransform txTranslate = CGAffineTransformMakeTranslation(
imageSize.height, 0.0);
CGAffineTransform txCompound = CGAffineTransformRotate(txTranslate,
M_PI_2);
return CGRectApplyAffineTransform(source, txCompound);
}
case UIImageOrientationDown: { // EXIF #3
CGAffineTransform txTranslate = CGAffineTransformMakeTranslation(
imageSize.width, imageSize.height);
CGAffineTransform txCompound = CGAffineTransformRotate(txTranslate,
M_PI);
return CGRectApplyAffineTransform(source, txCompound);
}
case UIImageOrientationRight: { // EXIF #6
CGAffineTransform txTranslate = CGAffineTransformMakeTranslation(
0.0, imageSize.width);
CGAffineTransform txCompound = CGAffineTransformRotate(txTranslate,
M_PI + M_PI_2);
return CGRectApplyAffineTransform(source, txCompound);
}
case UIImageOrientationUp: // EXIF #1 - do nothing
default: // EXIF 2,4,5,7 - ignore
return source;
}
cropImage 方法似乎适用于从互联网下载的图像（不包含任何方向信息）。
我的选项用完了。有人可以帮帮我吗？
The cropImage method seems to work for images downloaded from the internet (which don't contain any orientation info).
I am running out of options. Could someone PLEASE help me out?
感谢阅读！
推荐答案
如果可以的话，使用Core Graphics跳过图像会更容易：
When you can, it is easier to skip drawing images with Core Graphics:
- (UIImage *)cropImage:(UIImage *)oldImage {
CGSize imageSize = oldImage.size
UIGraphicsBeginImageContextWithOptions( CGSizeMake( imageSize.width,
imageSize.height - 200),
NO,
0.);
[oldImage drawAtPoint:CGPointMake( 0, -100)
blendMode:kCGBlendModeCopy
alpha:1.];
UIImage *croppedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return croppedImage;
}
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