I have some problems in rescaling the content of a UILabel object when it is stored as an image. Since the rendered image has to be bigger than the original UILabel, I have computed the scale imageScale needed to rescale the original image and saved it into a CGSize variable. In the following, I will explain the adopted (and failing) approaches.
Code used for rendering the image
The following code is used for rendering the extracted image on the canvas.
[labelImage drawInRect:CGRectMake(xCoordinate/imageScale.width,
yCoordinate/imageScale.height,
newSize.width,
newSize.height)
blendMode:kCGBlendModeNormal alpha:0.8];
where the variable newSize is computed as follows:
newSize.width = originalWidth/imageScale.width;
newSize.height = originalHeight/imageScale.height
Approach 1
I extracted the label using the following code:
UIGraphicsBeginImageContextWithOptions(newSize, NO, 0.0);
[[label layer] renderInContext: UIGraphicsGetCurrentContext()];
UIImage *snapshotImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
where label is the UILabel variable and newSize is the size that the rescaled image should have (see above for details).
However, I obtain the following image, which is obviously failing, since the content is very little and not centered:
Approach 2
I extracted the label using the following code:
UIGraphicsBeginImageContextWithOptions([label bounds].size, NO, 0.0);
[[label layer] renderInContext: UIGraphicsGetCurrentContext()];
UIImage *snapshotImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
However, since I am using the original image size in order to extract the image, the effect I obtain is the following:
As you can notice, the text in the balloon has not a high resolution, and thus it is not visualized properly.
The question
How to correct one of the two approaches so as to visualize in high resolution the image?
Seems like you just need to set appropriate scale for the generated image.
This is the function:
void UIGraphicsBeginImageContextWithOptions(
CGSize size,
BOOL opaque,
CGFloat scale
);
You set scale as 0.0. Try replacing it with [UIScreen mainScreen].scale.
Related
I'm rendering PDF content into a UIView and I'm seeing that the text provided by the PDF is blurry when zoomed.
The way I'm rendering the text is as follows
CGSize size = CGSizeMake(96, 9); // These numbers come from the PDF
NSString* text = #"Text to render";
UIGraphicsBeginImageContextWithOptions(size, NO, 0.0);
[text drawInRect:CGRectMake(0, 0, size.width, size.height)];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
This UIImage has the correct size and when I inspect it via XCode it is crisp.
When I call CGContextDrawImage below
CGRect widgetRect = CGRectMake(0,0,180,90);
CGContextDrawImage(mainContext, size, image.CGImage);
The result is blurry.
Notes:
The mainContext above has it's origin lower left so that's why I render text into a separate context and draw an image.
The UIView has a contentScaleFactor of 3 and the mainContext has a size to match that scale.
I looked at CGContextDrawImage draws large images very blurry and it doesn't address my problem.
I can't reproduce this problem outside my app in it's own.
This last part shows me that the problem is somewhere in the app code so I' hoping for hints and ideas about where to look in the rendering pipeline and how to debug.
EDIT:
Updated the calll to CGContextDrawImage to use the correct size.
I've been having issues rendering images with the UIImageView class. The pixelation seems to occur mostly on the edges of the image I am trying to show.
I have tried changing the property 'Render with edge antialiasing' to no avail.
The image files contain images that are larger than what will appear on the screen.
It seems to be royally messing with the quality of the image and then displaying it. I tried to post images here, but StackOverflow is denying me that privilege. So here's a link to what's going on.
http://i.imgur.com/QpUOTOF.png
The sun in this image is the problem I'm speaking of. Any ideas?
On-the-fly image resizing is quick and of low quality. For bundled images, it is worth the extra bundle space to include downsized versions. For downloaded images, you can achieve better results by resizing with Core Graphics into a new UIImage before you set the image property.
CGSize newSize = CGSizeMake(newWidth, newHeight);
UIGraphicsBeginImageContextWithOptions(newSize, // context size
NO, // opaque?
0); // image scale. 0 means "device screen scale"
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
[bigImage drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
Use following method use for get specific hight and width with image
+ (UIImage*)resizeImage:(UIImage*)image withWidth:(int)width withHeight:(int)height
{
CGSize newSize = CGSizeMake(width, height);
float widthRatio = newSize.width/image.size.width;
float heightRatio = newSize.height/image.size.height;
if(widthRatio > heightRatio)
{
newSize=CGSizeMake(image.size.width*heightRatio,image.size.height*heightRatio);
}
else
{
newSize=CGSizeMake(image.size.width*widthRatio,image.size.height*widthRatio);
}
UIGraphicsBeginImageContextWithOptions(newSize, NO, 0.0);
[image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
This method return NewImage, with specific size that you specified.
How big is your image and what is the size of the imageView? Don't rely on UIImageView to scale it down for you. You probably need to resize it manually. This would also be a bit more memory efficient.
I use categories like these:
>>>github link <<<
to do image resizing.
This also gives you some other nice function for rounded corners etc.
Also keep in mind, that you need a transparent border at the edge of an image if you want to rotate it to avoid aliasing.
In my app, I want to high quality Image. Image is loaded from Facebook friend list. When that image is loaded in smaller size (50 * 50), its quality is fine. But when I try to get that image in bigger size(280 *280) quality of image diminished.
For round corner m doing like :
self.mImageView.layer.cornerRadius = 10.0;
self.mImageView.layer.borderColor = [UIColor blackColor].CGColor;
self.mImageView.layer.borderWidth = 1.0;
self.mImageView.layer.masksToBounds = YES;
For getting image m using following code :
self.mImageView.image = [self imageWithImage:profileImage scaledToSize:CGSizeMake(280, 280)];
- (UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize {
UIGraphicsBeginImageContextWithOptions(newSize, YES,0.0);
CGContextRef context = CGContextRetain(UIGraphicsGetCurrentContext());
CGContextTranslateCTM(context, 0.0, newSize.height);
CGContextScaleCTM(context, 1.0, -1.0);
CGContextSetInterpolationQuality(context, kCGInterpolationLow);
CGContextSetAllowsAntialiasing (context, TRUE);
CGContextSetShouldAntialias(context, TRUE);
CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, newSize.width, newSize.height),image.CGImage);
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
I have checked my code several times, but could not figure out how to make image perfect. So, guys how this quality of image will be improved?
Thanx in advance...
…quality of image diminished.
The 'quality' of the image is still present. (Technically, you are introducing a small amount of error by resizing it, but that's not the real problem…)
So, you want to scale a 50x50px image to 280x280px? The information/detail does not exist in the source signal. Ideally, you would download a more appropriately sized image, for the size you want to display at.
If that's not an option, you could reduce pixelation by means of proper resampling and/or interpolation. This would simply smooth out the pixels your program magnifies by 5.6 -- the image would then look like a cross between pixelated and blurred (see CGContextSetAllowsAntialiasing, CGContextSetShouldAntialias, CGContextSetInterpolationQuality and related APIs to accomplish this using quartz).
I have a view (called outPutView) that contains graphics, like uIImageViews and labels. I need to render an image of the outPutView and it's sub-views. I am using renderInContext:UIGraphicsGetCurrentContext() to do so. Works fine, except that I need to scale the views. I am using a transform on the outPutView. This successfully scales the view and it's sub-views, but the transform does not render. While the views are scaled onscreen. the final render displays the vies at their original size, while the render context is at the target size (here #2x iPhone view size).
Thanks for reading!!
[outPutView setTransform:CGAffineTransformMake(2, 0, 0, 2, 0, 0)];
CGSize renderSize = CGSizeMake(self.view.bounds.size.width*2, self.view.bounds.size.height*2);
UIGraphicsBeginImageContext(renderSize);
[[outPutView layer] renderInContext:UIGraphicsGetCurrentContext()];
renderedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
I've just made this work, although in the opposite direction (scaling down). Here's a summary of the relevant code:
// destination size is half of self (self is a UIView)
float rescale = 0.5;
CGSize resize = CGSizeMake(self.width * rescale, self.height * rescale);
// make the destination context
UIGraphicsBeginImageContextWithOptions(resize, YES, 0);
// apply the scale to dest context
CGContextScaleCTM(UIGraphicsGetCurrentContext(), rescale, rescale);
// render self into dest context
[self.layer renderInContext:UIGraphicsGetCurrentContext()];
// grab the resulting UIImage
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
To scale up instead of down, it should be fine to have rescale = 2.
I solved this by re-ordering my views. Actually adding another view between the output view: the view that the rendered context is taken from, and the view that is scaled via transform. It worked, but I have no idea why at this point. Any thoughts on this would be appreciated. Thanks for reading.
I have found the following code to resize an UIImage:
CGSize newSize = CGSizeMake(self.image.size.width*0.25, self.image.size.height*0.25);
UIGraphicsBeginImageContextWithOptions(newSize, NO, 0.0);
[self.image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
self.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
but there are some couple of things I don't understand.
First I'm trying to resize the original image to 25% of the original size - but this method resizes it to 50% of the original size. Why?
What is the connection between drawInRect and UIGraphicsGetImageFromCurrentImageContext. As I see it, the UIGraphicsGetImageFromCurrentImageContext is overwriting the current image making the call to drawInRect redundant.
I would be grateful if someone could help me understand what's going on in details.
Thanks in advance.
first , because it's retina screen, you should set the scale to 1.0 , or it just x2
UIGraphicsBeginImageContextWithOptions(newSize, NO, 1.0);
if you call UIGraphicsBeginImageContext , any paint work will result in the Context you specific
the drawInRect in your code paint the image to the context, it's not redundant
or you can remove it, you get a empty image
finally, you can get a merged UIImage from the context
UIGraphicsGetImageFromCurrentImageContext();
just get a UIImage From What you have done(on context)
if you don't set the image back , it's won't change anything
self.image = UIGraphicsGetImageFromCurrentImageContext();