I need to form an image by composing some visual elements and save it on disk. The question is: how to "screenshot" a certain area of a view? Possibly a view that is not visible, so the procedure can be executed unnoticed?
This code snippet shows how to render a view to a UIImage:
UIGraphicsBeginImageContext(myView.bounds.size);
[myView.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
And this snippet shows how to save a UIImage as a JPEG or a PNG:
NSString *pngPath = [NSHomeDirectory()
stringByAppendingPathComponent:#"Documents/Test.png"];
NSString *jpgPath = [NSHomeDirectory()
stringByAppendingPathComponent:#"Documents/Test.jpg"];
[UIImageJPEGRepresentation(viewImage, 1.0) writeToFile:jpgPath atomically:YES];
[UIImagePNGRepresentation(viewImage) writeToFile:pngPath atomically:YES];
Related
I am cutting up a large image and saving it into many different images. I first implemented this in iOS and it is working fine, but when I try and port the code to OSX, a thin white line (1 pixel) appears on the top and right of the image. The line is not pure white, or solid (see sample below).
Here is the iOS code to make one sub-image, that works like a champ:
-(void)testMethod:(int)page forRect:(CGRect)rect{
NSString *filePath = #"imageName";
NSData *data = [HeavyResourceManager dataForPath:filePath];//this just gets the image as NSData
UIImage *image = [UIImage imageWithData:data];
CGImageRef imageRef = CGImageCreateWithImageInRect([image CGImage], rect);//crop in the rect
UIImage *result = [UIImage imageWithCGImage:imageRef scale:0 orientation:image.imageOrientation];
CGImageRelease(imageRef);
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectoryPath = [paths objectAtIndex:0];
[UIImageJPEGRepresentation(result, 1.0) writeToFile:[documentsDirectoryPath stringByAppendingPathComponent::#"output.jpg"] atomically:YES];
}
Here is the ported code in OSX that causes the white lines to be added:
NSImage *source = [[[NSImage alloc]initWithContentsOfFile:imagePath] autorelease];
//init the image
NSImage *target = [[[NSImage alloc]initWithSize:panelRect.size] autorelease];
//start drawing
[target lockFocus];
[source drawInRect:NSMakeRect(0,0,panelRect.size.width,panelRect.size.height)
fromRect:NSMakeRect(panelRect.origin.x , source.size.height - panelRect.origin.y - panelRect.size.height, panelRect.size.width, panelRect.size.height)
operation:NSCompositeCopy
fraction:1.0];
[target unlockFocus];
//create a NSBitmapImageRep
NSBitmapImageRep *bmpImageRep = [[[NSBitmapImageRep alloc]initWithData:[target TIFFRepresentation]] autorelease];
//write to tiff
[[target TIFFRepresentation] writeToFile:#"outputImage.tiff" atomically:NO];
[target addRepresentation:bmpImageRep];
NSDictionary *imageProps = [NSDictionary dictionaryWithObject:[NSNumber numberWithFloat:1.0] forKey:NSImageCompressionFactor];
//get the data from the representation
NSData *data = [bmpImageRep representationUsingType: NSJPEGFileType
properties: imageProps];
//write the data to a file
[data writeToFile: #"outputImage.jpg" atomically:NO];
data = [bmpImageRep representationUsingType: NSPNGFileType properties: imageProps];
//write the data to png
[data writeToFile: #"outputImage.png" atomically:NO];
The above code saves the image to three different formats to check if the problem was not in the save process of a specific format. It does not seem to be because all the formats have the same problem.
Here is a blown up (4x) version of top right hand corner of the images:
(OSX, note the white line top and left. It looks like a blur here, because the image is blown up)
(iOS, note there are no white lines)
If someone could tell me why this might be happening, I would be very happy. Perhaps it has something to do with the quality difference (the OSX version seems lower quality - though you can't notice)? Perhaps there is a completely different way to do this?
For reference, here is the unscaled osx image:
Update: Thanks to Daij-Djan, I was able to stop the drawInRect method from antialiasing:
//start drawing on target
[target lockFocus];
[NSGraphicsContext saveGraphicsState];
[[NSGraphicsContext currentContext]
setImageInterpolation:NSImageInterpolationNone];
[[NSGraphicsContext currentContext] setShouldAntialias:NO];
//draw the portion of the source image on target image
[source drawInRect:NSMakeRect(0,0,panelRect.size.width,panelRect.size.height)
fromRect:NSMakeRect(panelRect.origin.x , source.size.height - panelRect.origin.y - panelRect.size.height, panelRect.size.width, panelRect.size.height)
operation:NSCompositeDestinationAtop
fraction:1.0];
[NSGraphicsContext restoreGraphicsState];
//end drawing
[target unlockFocus];
Update: Changed 'Interpolation' to NSImageInterpolationNone, as this gives a better representation. The high interpolation makes minor adjustments, which is noticeable when zooming in on text. Removing interpolation stops pixels from jumping around, but still, there is a little difference in the color (164 to 155 for a grey color). Would be great to be able to just cut up an image like I can in iOS...
it looks like antialiasing... you gotta round the float values you calculate when cutting/scaling the image.
use froundf() on the float values
I'm trying to move some image loading into the background. Currently i'm loading UIImages in the background but from what I have read, this is not the suggested way to go about doing it, instead I should load the CGImageRef in the background, then load the UIImage from it in the main thread.
The problem is that when I try to create a CGImageRef, its coming back as null. Sample code:
NSData * imageData = [NSData dataWithContentsOfFile: coverPath];
if(nil != imageData)
{
UIImage * uiImage = [UIImage imageWithData: imageData];
CGDataProviderRef provider = CGDataProviderCreateWithCFData((__bridge CFDataRef) imageData);
CGImageRef imageRef = CGImageCreateWithPNGDataProvider(provider, NULL, true, kCGRenderingIntentDefault);
NSLog(#"Test: %p, %p", imageRef, uiImage);
CGDataProviderRelease(provider);
}
Which logs out Test: 0x0, 0x1c566bb0. Meaning the imageRef is null but the uiImage is not. Any ideas what i'm doing wrong here? It seems as if this should be quite simple?
CGImageCreateWithPNGDataProvider()
returns nil if the provided data is not in PNG format (for example JPEG or TIFF).
[UIImage imageWithData: imageData]
returns an image for all supported image file formats (PNG, JPEG, TIFF etc.)
This explains why the first function can fail while the second succeeds.
I have two methods, first checks if I've already downloaded the image, and if not retrieves the image from a URL and caches it to my docs directory in my app. If it has been, it simply retrieves it, and if I have a internet connection, will re-download it. Here are the two methods:
- (UIImage *) getImageFromUserIMagesFolderInDocsWithName:(NSString *)nameOfFile
{
UIImage *image = [UIImage imageNamed:nameOfFile];
if (!image) // image doesn't exist in bundle...
{
// Get Image
NSString *cleanNameOfFile = [[[nameOfFile stringByReplacingOccurrencesOfString:#"." withString:#""]
stringByReplacingOccurrencesOfString:#":" withString:#""]
stringByReplacingOccurrencesOfString:#"/" withString:#""];
NSString *filePath = [NSHomeDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:#"Documents/%#.png", cleanNameOfFile]];
image = [[UIImage alloc] initWithData:[NSData dataWithContentsOfFile:filePath]];
if (!image)
{
// image isn't cached
image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:nameOfFile]]];
[self saveImageToUserImagesFolderInDocsWithName:cleanNameOfFile andImage:image];
}
else
{
// if we have a internet connection, update the cached image
/*if (isConnectedToInternet) {
image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:nameOfFile]]];
[self saveImageToUserImagesFolderInDocsWithName:cleanNameOfFile andImage:image];
}*/
// otherwise just return it
}
}
return image;
}
Here's to save the image
- (void) saveImageToUserImagesFolderInDocsWithName:(NSString *)nameOfFile andImage:(UIImage *)image
{
NSString *pngPath = [NSHomeDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:#"Documents/%#.png", nameOfFile]];
[UIImagePNGRepresentation(image) writeToFile:pngPath atomically:YES];
NSLog(#"directory: %#", [[UIImage alloc] initWithContentsOfFile:pngPath]);
}
The image has already been successfully downloaded and cached to my documents directory (I know because I can see it in the File system). And it successfully re loads the image the first time I call this method, but once I go to another view, and re-call this method when I come back to the same view, it's blank. Yet, the URL is correct. What's wrong here?
1) You should not be writing into a hardcoded path as you do (ie "Documents/xxx"), but rather ask for the Application Support directory, use it, and also mark files so that they don't get uploaded to iCloud (unless you want that). See this link on the specifics. Create a subfolder in it and mark it as not for iCloud backup.
2) Try changing:
image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:nameOfFile]]];
to
image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:filePath]]];
Maybe, you should do:
image = [UIImage imageWithContentsOfFile: nameOfFile];
How can I draw to an image in objective-c? all I need to do is create an image with a size I set, draw few AA lines and save the image to a png file. I tried to find it in apple docs but there are CGImage, NSImage, CIImage and more. which one is easiest for my goal? I only need to support the latest mac os x version so new things are not a problem.
Probably the easiest way is to use an NSImage and draw directly into it after calling lockFocus.
Example:
NSSize imageSize = NSMakeSize(512, 512);
NSImage *image = [[[NSImage alloc] initWithSize:imageSize] autorelease];
[image lockFocus];
//draw a line:
[NSBezierPath strokeLineFromPoint:NSMakePoint(100, 100) toPoint:NSMakePoint(200, 200)];
//...
NSBitmapImageRep *imageRep = [[[NSBitmapImageRep alloc] initWithFocusedViewRect:NSMakeRect(0, 0, imageSize.width, imageSize.height)] autorelease];
NSData *pngData = [imageRep representationUsingType:NSPNGFileType properties:nil];
[image unlockFocus];
[pngData writeToFile:#"/path/to/your/file.png" atomically:YES];
Well your question is actually two questions in one.
First question is about how to draw an image. You should first read the docs about drawing images. Apple has a Cocoa Drawing Guide about this topic. Start from there to draw images.
Then you need to save the image to disk. Here is a nice piece of code from over here:
NSBitmapImageRep *bits = ...; // get a rep from your image, or grab from a view
NSData *data;
data = [bits representationUsingType: NSPNGFileType
properties: nil];
[data writeToFile: #"/path/to/wherever/test.png"
atomically: NO];
I am loading files that are downloaded from the web in a UIWebView (HTML files).
Is there a way to create a UIImage from an HTML file located in the Documents folder?
The goal is to auto generate thumbnails without needing to manual create them...
Update
My train of thought would be to do something in the line of:
NSString * s = [[NSBundle mainBundle] pathForResource:#"test" ofType:#"html"];
UIImage *image = [[UIImage alloc] initWithData:
[NSData dataWithContentsOfURL:url]];
Which of course does not work in this case!
Thanks!
S.
I found this solution here
UIGraphicsBeginImageContext(yourWebView.bounds.size);
[yourWebView.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *resultImageView = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
resultImageView will be an image that contains the render of yourWebView.
If you want to shrink it down to a thumbnail size from there, I like Trevor's UIImage category for that purpose.