I have an NSImage that I would like to save as a PNG, but remove the alpha channel and use 5 bit colour. I am currently doing this to create my PNG:
NSData *imageData = [image TIFFRepresentation];
NSBitmapImageRep *imageRep = [NSBitmapImageRep imageRepWithData:imageData];
NSDictionary *imageProps = nil;
imageData = [imageRep representationUsingType:NSPNGFileType properties:imageProps];
[imageData writeToFile:fileNameWithExtension atomically:YES];
I've read though lots of similar questions on SO but am confused as to the best/correct approach to use. Do I create a new CGGraphics context and draw into that? Can I create a new imageRep with these parameters directly? Any help, with a code snippet would be greatly appreciated.
Cheers
Dave
I did this in the end. Looks ugly and smells to me. Any better suggestions greatly appreciated.
// Create a graphics context (5 bits per colour, no-alpha) to render the tile
static int const kNumberOfBitsPerColour = 5;
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef tileGraphicsContext = CGBitmapContextCreate (NULL, rect.size.width, rect.size.height, kNumberOfBitsPerColour, 2 * rect.size.width, colorSpace, kCGBitmapByteOrder16Little | kCGImageAlphaNoneSkipFirst);
// Draw the clipped part of the image into the tile graphics context
NSData *imageData = [clippedNSImage TIFFRepresentation];
CGImageRef imageRef = [[NSBitmapImageRep imageRepWithData:imageData] CGImage];
CGContextDrawImage(tileGraphicsContext, rect, imageRef);
// Create an NSImage from the tile graphics context
CGImageRef newImage = CGBitmapContextCreateImage(tileGraphicsContext);
NSImage *newNSImage = [[NSImage alloc] initWithCGImage:newImage size:rect.size];
// Clean up
CGImageRelease(newImage);
CGContextRelease(tileGraphicsContext);
CGColorSpaceRelease(colorSpace);
Related
I got a UIImage from UIImagePickerController, and using the code from this site to resize the image
- (UIImage *)resizedImage:(CGSize)newSize
transform:(CGAffineTransform)transform
drawTransposed:(BOOL)transpose
interpolationQuality:(CGInterpolationQuality)quality {
CGRect newRect = CGRectIntegral(CGRectMake(0, 0, newSize.width, newSize.height));
CGRect transposedRect = CGRectMake(0, 0, newRect.size.height, newRect.size.width);
CGImageRef imageRef = self.CGImage;
// Build a context that's the same dimensions as the new size
CGContextRef bitmap = CGBitmapContextCreate(NULL,
newRect.size.width,
newRect.size.height,
CGImageGetBitsPerComponent(imageRef),
0,
CGImageGetColorSpace(imageRef),
CGImageGetBitmapInfo(imageRef));
// Rotate and/or flip the image if required by its orientation
CGContextConcatCTM(bitmap, transform);
// Set the quality level to use when rescaling
CGContextSetInterpolationQuality(bitmap, quality);
// Draw into the context; this scales the image
CGContextDrawImage(bitmap, transpose ? transposedRect : 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;
}
UIImagePNGRepresentation() failed to return NSData on re-sized image, but UIImageJPEGRepresentation() succeed.
How do we know if a UIImage is presentable in PNG or JPEG? What missed in the above code that make the resized image can not be represented in PNG?
According to apple document: "This function may return nil if the image has no data or if the underlying CGImageRef contains data in an unsupported bitmap format."
What bitmap format supported by PNG presentation? How to make an UIImage PNG-supported format?
That was a mistake that in another part of the code the image was rescaled with the following
CGContextRef context = CGBitmapContextCreate(NULL,
size.width,
size.height,
8,
0,
CGImageGetColorSpace(source),
kCGImageAlphaNoneSkipFirst);
Changing kCGImageAlphaNoneSkipFirst to CGImageGetBitmapInfo(source) fixed the problem
go to following link...
How to check if downloaded PNG image is corrupt?
it may help you...
Let me know it is working or not...
Happy Coding!!!!
I'm processing images (using AVFoundation and OpenCV on iOS) and I want to simply display contents of CMSampleBufferRef (or IplImage) to screen.
Simply: I just want to display (like with OpenCV's cvShowImage()) non-converted image to see if I'm not dealing with corrupted or somehow deformed image.
Sadly not. Different bitmap representation.
Perhaps you want a category? I use something along the lines of this:
// NSImage+OpenCV.h
#interface NSImage (OpenCV)
+ (NSImage*)imageWithCVMat:(const cv::Mat&)cvMat;
- (id)initWithCVMat:(const cv::Mat&)cvMat;
- (cv::Ptr<cv::Mat>)cvMat;
#end
// NSImage+OpenCV.m
using namespace cv;
#implementation NSImage (OpenCV)
- (id)initWithCVMat:(const cv::Mat&)cvMat {
NSData *data = [NSData dataWithBytes:cvMat.data
length:cvMat.total()*cvMat.elemSize()];
CGDataProviderRef provider = CGDataProviderCreateWithCFData((__bridge CFDataRef)data);
CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
CGImageRef imageRef = CGImageCreate(cvMat.cols,
cvMat.rows,
8,
8 * cvMat.elemSize(),
cvMat.step[0],
colourSpace,
kCGImageAlphaNone |
kCGBitmapByteOrderDefault,
provider,
NULL,
false,
kCGRenderingIntentDefault);
NSImage *image = [[NSImage alloc] initWithCGImage:imageRef size:CGSizeMake(cvMat.cols,cvMat.rows)];
CGColorSpaceRelease(colourSpace);
CGDataProviderRelease(provider);
CGImageRelease(imageRef);
return image;
}
+(NSImage*)imageWithCVMat:(const cv::Mat&)cvMat {
return [[NSImage alloc] initWithCVMat:cvMat];
}
- (cv::Ptr<cv::Mat>)cvMat {
CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)[self TIFFRepresentation], NULL);
CGImageRef imageRef = CGImageSourceCreateImageAtIndex(source, 0, NULL);
cv::Ptr<cv::Mat> cvMat = new cv::Mat(self.size.height, self.size.width, CV_8UC4);
CGContextRef contextRef = CGBitmapContextCreate(cvMat->data,
cvMat->cols,
cvMat->rows,
8,
cvMat->step[0],
CGImageGetColorSpace(imageRef),
kCGImageAlphaNoneSkipLast |
kCGBitmapByteOrderDefault);
CGContextDrawImage(contextRef,
CGRectMake(0, 0, cvMat->cols, cvMat->rows),
imageRef);
CGContextRelease(contextRef);
CGImageRelease(imageRef);
return cvMat;
}
#end
I created a masked image using a function form an iphone blog:
UIImage *imgToSave = [self maskImage:[UIImage imageNamed:#"pic.jpg"] withMask:[UIImage imageNamed:#"sd-face-mask.png"]];
Looks good in a UIImageView
UIImageView *imgView = [[UIImageView alloc] initWithImage:imgToSave];
imgView.center = CGPointMake(160.0f, 140.0f);
[self.view addSubview:imgView];
UIImagePNGRepresentation to save to disk:
[UIImagePNGRepresentation(imgToSave) writeToFile:[self findUniqueSavePath] atomically:YES];
UIImagePNGRepresentation returns NSData of an image that looks different.
The output is inverse image mask.
The area that was cut out in the app is now visible in the file.
The area that was visible in the app is now removed. Visibility is opposite.
My mask is designed to remove everything but the face area in the picture. The UIImage looks right in the app but after I save it on disk, the file looks opposite. The face is removed but everything else this there.
Please let me know if you can help!
In quartz you cam mask either by an image mask (black let through and white blocks), or a normal image (white let through and black blocks) which is the opposite. It seems for some reason saving is treating the image mask as a normal image to mask with. One thought is to render to a bitmap context and then create an image to be saved from that.
I had the exact same issue, when I saved the file it was one way, but the image returned in memory was the exact opposite.
The culprit & the solution was UIImagePNGRepresentation(). It fixes the in-app image before saving it to disk, so I just inserted that function as the last step in creating the masked image and returning that.
This may not be the most elegant solution, but it works. I copied some code from my app and condensed it, not sure if this code below works as is, but if not, its close... maybe just some typos.
Enjoy. :)
// MyImageHelperObj.h
#interface MyImageHelperObj : NSObject
+ (UIImage *) createGrayScaleImage:(UIImage*)originalImage;
+ (UIImage *) createMaskedImageWithSize:(CGSize)newSize sourceImage:(UIImage *)sourceImage maskImage:(UIImage *)maskImage;
#end
// MyImageHelperObj.m
#import <QuartzCore/QuartzCore.h>
#import "MyImageHelperObj.h"
#implementation MyImageHelperObj
+ (UIImage *) createMaskedImageWithSize:(CGSize)newSize sourceImage:(UIImage *)sourceImage maskImage:(UIImage *)maskImage;
{
// create image size rect
CGRect newRect = CGRectZero;
newRect.size = newSize;
// draw source image
UIGraphicsBeginImageContextWithOptions(newRect.size, NO, 0.0f);
[sourceImage drawInRect:newRect];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
// draw mask image
[maskImage drawInRect:newRect blendMode:kCGBlendModeNormal alpha:1.0f];
maskImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
// create grayscale version of mask image to make the "image mask"
UIImage *grayScaleMaskImage = [MyImageHelperObj createGrayScaleImage:maskImage];
CGFloat width = CGImageGetWidth(grayScaleMaskImage.CGImage);
CGFloat height = CGImageGetHeight(grayScaleMaskImage.CGImage);
CGFloat bitsPerPixel = CGImageGetBitsPerPixel(grayScaleMaskImage.CGImage);
CGFloat bytesPerRow = CGImageGetBytesPerRow(grayScaleMaskImage.CGImage);
CGDataProviderRef providerRef = CGImageGetDataProvider(grayScaleMaskImage.CGImage);
CGImageRef imageMask = CGImageMaskCreate(width, height, 8, bitsPerPixel, bytesPerRow, providerRef, NULL, false);
CGImageRef maskedImage = CGImageCreateWithMask(newImage.CGImage, imageMask);
CGImageRelease(imageMask);
newImage = [UIImage imageWithCGImage:maskedImage];
CGImageRelease(maskedImage);
return [UIImage imageWithData:UIImagePNGRepresentation(newImage)];
}
+ (UIImage *) createGrayScaleImage:(UIImage*)originalImage;
{
//create gray device colorspace.
CGColorSpaceRef space = CGColorSpaceCreateDeviceGray();
//create 8-bit bimap context without alpha channel.
CGContextRef bitmapContext = CGBitmapContextCreate(NULL, originalImage.size.width, originalImage.size.height, 8, 0, space, kCGImageAlphaNone);
CGColorSpaceRelease(space);
//Draw image.
CGRect bounds = CGRectMake(0.0, 0.0, originalImage.size.width, originalImage.size.height);
CGContextDrawImage(bitmapContext, bounds, originalImage.CGImage);
//Get image from bimap context.
CGImageRef grayScaleImage = CGBitmapContextCreateImage(bitmapContext);
CGContextRelease(bitmapContext);
//image is inverted. UIImage inverts orientation while converting CGImage to UIImage.
UIImage* image = [UIImage imageWithCGImage:grayScaleImage];
CGImageRelease(grayScaleImage);
return image;
}
#end
I'm using the following code to crop and create a new UIImage out of a bigger one. I've isolated the issue to be with the function CGImageCreateWithImageInRect() which seem to not set some CGImage property the way I want. :-) The problem is that a call to function UIImagePNGRepresentation() fails returning a nil.
CGImageRef origRef = [stillView.image CGImage];
CGImageRef cgCrop = CGImageCreateWithImageInRect( origRef, theRect);
UIImage *imgCrop = [UIImage imageWithCGImage:cgCrop];
...
NSData *data = UIImagePNGRepresentation ( imgCrop);
-- libpng error: No IDATs written into file
Any idea what might wrong or alternative for cropping a rect out of UIImage?
I had the same problem, but only when testing compatibility on iOS 3.2. On 4.2 it works fine.
In the end I found this http://www.hive05.com/2008/11/crop-an-image-using-the-iphone-sdk/ which works on both, albeit a little more verbose!
I converted this into a category on UIImage:
UIImage+Crop.h
#interface UIImage (Crop)
- (UIImage*) imageByCroppingToRect:(CGRect)rect;
#end
UIImage+Crop.m
#implementation UIImage (Crop)
- (UIImage*) imageByCroppingToRect:(CGRect)rect
{
//create a context to do our clipping in
UIGraphicsBeginImageContext(rect.size);
CGContextRef currentContext = UIGraphicsGetCurrentContext();
//create a rect with the size we want to crop the image to
//the X and Y here are zero so we start at the beginning of our
//newly created context
CGRect clippedRect = CGRectMake(0, 0, rect.size.width, rect.size.height);
CGContextClipToRect( currentContext, clippedRect);
//create a rect equivalent to the full size of the image
//offset the rect by the X and Y we want to start the crop
//from in order to cut off anything before them
CGRect drawRect = CGRectMake(rect.origin.x * -1,
rect.origin.y * -1,
self.size.width,
self.size.height);
//draw the image to our clipped context using our offset rect
CGContextTranslateCTM(currentContext, 0.0, rect.size.height);
CGContextScaleCTM(currentContext, 1.0, -1.0);
CGContextDrawImage(currentContext, drawRect, self.CGImage);
//pull the image from our cropped context
UIImage *cropped = UIGraphicsGetImageFromCurrentImageContext();
//pop the context to get back to the default
UIGraphicsEndImageContext();
//Note: this is autoreleased
return cropped;
}
#end
In a PNG there are various chunks present, some containing palette info, some actual image data and some other information, it's a very interesting standard. The IDAT chunk is the bit that actually contains the image data. If there's no "IDAT written into file" then libpng has had some issue creating a PNG from the input data.
I don't know exactly what your stillView.image is, but what happens when you pass your code a CGImageRef that is certainly valid? What are the actual values in theRect? If your theRect is beyond the bounds of the image then the cgCrop you're trying to use to make the UIImage could easily be nil - or not nil, but containing no image or an image with width and height 0, giving libpng nothing to work with.
It seems the solution you are trying should work, but I recommend to use this:
CGImageRef image = [stillView.image CGImage];
CGRect cropZone;
size_t cWitdh = cropZone.size.width;
size_t cHeight = cropZone.size.height;
size_t bitsPerComponent = CGImageGetBitsPerComponent(image);
size_t bytesPerRow = CGImageGetBytesPerRow(image) / CGImageGetWidth(image) * cWidth;
//Now we build a Context with those dimensions.
CGContextRef context = CGBitmapContextCreate(nil, cWitdh, cHeight, bitsPerComponent, bytesPerRow, CGColorSpaceCreateDeviceRGB(), CGImageGetBitmapInfo(image));
CGContextDrawImage(context, cropZone, image);
CGImageRef result = CGBitmapContextCreateImage(context);
UIImage * cropUIImage = [[UIImage alloc] initWithCGImage:tmp];
CGContextRelease(context);
CGImageRelease(mergeResult);
NSData * imgData = UIImagePNGRepresentation ( cropUIImage);
UIImage *croppedImage = [self imageByCropping:yourImageView.image toRect:heredefineyourRect];
CGSize size = CGSizeMake(croppedImage.size.height, croppedImage.size.width);
UIGraphicsBeginImageContext(size);
CGPoint pointImg1 = CGPointMake(0,0);
[croppedImage drawAtPoint:pointImg1 ];
[[UIImage imageNamed:yourImagenameDefine] drawInRect:CGRectMake(0,532, 150,80) ];//here define your Reactangle
UIImage* result = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
croppedImage = result;
yourCropImageView.image=croppedImage;
[yourCropImageView.image retain];
I have a buffer which has JPEG image data. I need to display this image in UIImageView. I need to convert this image buffer into an object of UIImage and use it as follows
NSData *data = [NSData dataWithContentsOfFile:appFile];
UIImage *theImage = [[UIImage alloc] initWithData:data];
I get the image displayed but with a low resolution as compared to the actual resolution. Do I need to convert it into a Bitmap first and then use it with UIImage? I don't seem to be able to use NSBitmapImageRep. Any ideas on how can this be achieved?
If the UIImageView frame dimensions are different than the source image dimensions, you'll get a resized version of the image. The quality can be pretty rough depending on how much of a conversion is being performed.
I found this code on the net somewhere (sorry original author - I've lost the attribution) that performs a smoother resize:
UIImage* resizedImage(UIImage *inImage, CGRect thumbRect)
{
CGImageRef imageRef = [inImage CGImage];
CGImageAlphaInfo alphaInfo = CGImageGetAlphaInfo(imageRef);
// There's a wierdness with kCGImageAlphaNone and CGBitmapContextCreate
// see Supported Pixel Formats in the Quartz 2D Programming Guide
// Creating a Bitmap Graphics Context section
// only RGB 8 bit images with alpha of kCGImageAlphaNoneSkipFirst, kCGImageAlphaNoneSkipLast, kCGImageAlphaPremultipliedFirst,
// and kCGImageAlphaPremultipliedLast, with a few other oddball image kinds are supported
// The images on input here are likely to be png or jpeg files
if (alphaInfo == kCGImageAlphaNone)
alphaInfo = kCGImageAlphaNoneSkipLast;
// Build a bitmap context that's the size of the thumbRect
CGContextRef bitmap = CGBitmapContextCreate(
NULL,
thumbRect.size.width, // width
thumbRect.size.height, // height
CGImageGetBitsPerComponent(imageRef), // really needs to always be 8
4 * thumbRect.size.width, // rowbytes
CGImageGetColorSpace(imageRef),
alphaInfo
);
// Draw into the context, this scales the image
CGContextDrawImage(bitmap, thumbRect, imageRef);
// Get an image from the context and a UIImage
CGImageRef ref = CGBitmapContextCreateImage(bitmap);
UIImage* result = [UIImage imageWithCGImage:ref];
CGContextRelease(bitmap); // ok if NULL
CGImageRelease(ref);
return result;
}