I'm writing this Today Widget, that needs to display an image.
I noticed, that every time the Widget loads, the image is redrawn. This takes about half a second.
After some investigation, I found out, that the culprit is, that the image file is in the Indexed color space.
So: my question is:
How do I convert this file to something that the iPhone can display more efficiently? For instance, an RGB file. I would then save it to a new file, and load that new file in my UIImageView.
I played around a bit with CGImage, since I believe that is the solution direction, but I end up with a white UIImageView.
This is my code:
UIImage * theCartoon = [UIImage imageWithData:imageData];
CGImageRef si = [theCartoon CGImage];
CGDataProviderRef src = CGImageGetDataProvider(si);
CGImageRef imageRef = CGImageCreateWithPNGDataProvider(src, NULL, NO, kCGRenderingIntentDefault);
cartoon.image = [[UIImage alloc] initWithCGImage:imageRef];
Any suggestions on this approach? Some obvious misprogramming?
Try this
// The source image
CGImageRef image = theCartoon.CGImage;
CGSize size = CGSizeMake(CGImageGetWidth(image), CGImageGetHeight(image));
// The result image in RGB color space
CGImageRef result = nil;
// Check color space
CGColorSpaceRef srcColorSpace = CGImageGetColorSpace(image);
if (CGColorSpaceGetModel(srcColorSpace) != kCGColorSpaceModelRGB) {
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(nil, size.width, size.height, 8, 0, colorSpace, kCGImageAlphaNoneSkipLast);
CGRect rect = {CGPointZero, size};
CGContextDrawImage(context, rect, image);
result = CGBitmapContextCreateImage(context);
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
}
It's been a while since the question was asked, but for others who might need this, here is my solution:
-(UIImage *) convertIndexedColorSpaceToRGB:(UIImage *) sourceImage {
CGImageRef originalImageRef = sourceImage.CGImage;
const CGBitmapInfo originalBitmapInfo = CGImageGetBitmapInfo(originalImageRef);
// See: http://stackoverflow.com/questions/23723564/which-cgimagealphainfo-should-we-use
const uint32_t alphaInfo = (originalBitmapInfo & kCGBitmapAlphaInfoMask);
CGBitmapInfo bitmapInfo = originalBitmapInfo;
switch (alphaInfo)
{
case kCGImageAlphaNone:
bitmapInfo |= kCGBitmapByteOrder32Big | kCGImageAlphaNoneSkipLast;
break;
case kCGImageAlphaPremultipliedFirst:
case kCGImageAlphaPremultipliedLast:
case kCGImageAlphaNoneSkipFirst:
case kCGImageAlphaNoneSkipLast:
break;
case kCGImageAlphaOnly:
case kCGImageAlphaLast:
case kCGImageAlphaFirst:
{
return sourceImage;
}
break;
}
const CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
const CGSize pixelSize = CGSizeMake(sourceImage.size.width * sourceImage.scale, sourceImage.size.height * sourceImage.scale);
const CGContextRef context = CGBitmapContextCreate(NULL,
pixelSize.width,
pixelSize.height,
CGImageGetBitsPerComponent(originalImageRef),
pixelSize.width*4,
colorSpace,
bitmapInfo
);
CGColorSpaceRelease(colorSpace);
if (!context) return sourceImage;
const CGRect imageRect = CGRectMake(0, 0, pixelSize.width, pixelSize.height);
UIGraphicsPushContext(context);
// Flip coordinate system. See: http://stackoverflow.com/questions/506622/cgcontextdrawimage-draws-image-upside-down-when-passed-uiimage-cgimage
CGContextTranslateCTM(context, 0, pixelSize.height);
CGContextScaleCTM(context, 1.0, -1.0);
[sourceImage drawInRect:imageRect];
UIGraphicsPopContext();
const CGImageRef decompressedImageRef = CGBitmapContextCreateImage(context);
CGContextRelease(context);
UIImage *image = [UIImage imageWithCGImage:decompressedImageRef scale:[UIScreen mainScreen].scale orientation:UIImageOrientationUp];
CGImageRelease(decompressedImageRef);
return image; }
I'm using VLCKit to play video in my app, and I need to be able to take a screenshot of the video at certain points. This is the code I'm using:
-(NSData*)generateThumbnail{
int s = 1;
UIScreen* screen = [UIScreen mainScreen];
if ([screen respondsToSelector:#selector(scale)]) {
s = (int) [screen scale];
}
GLint viewport[4];
glGetIntegerv(GL_VIEWPORT, viewport);
int width = viewport[2];
int height = [_profile.resolution integerValue];//viewport[3];
int myDataLength = width * height * 4;
GLubyte *buffer = (GLubyte *) malloc(myDataLength);
GLubyte *buffer2 = (GLubyte *) malloc(myDataLength);
glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
for(int y1 = 0; y1 < height; y1++) {
for(int x1 = 0; x1 <width * 4; x1++) {
buffer2[(height - 1 - y1) * width * 4 + x1] = buffer[y1 * 4 * width + x1];
}
}
free(buffer);
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer2, myDataLength, NULL);
int bitsPerComponent = 8;
int bitsPerPixel = 32;
int bytesPerRow = 4 * width;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
CGImageRef imageRef = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
CGColorSpaceRelease(colorSpaceRef);
CGDataProviderRelease(provider);
UIImage *image = [ UIImage imageWithCGImage:imageRef scale:s orientation:UIImageOrientationUp ];
NSData *thumbAsData = UIImageJPEGRepresentation(image, 5);
return thumbAsData;
}
To be honest, I have no idea how most of this works. I copied it from somewhere a while ago (I don't remember the source). It mostly works, however frequently it seems parts of the image are missing.
Can someone point me in the right direction? Most of the other posts I see regarding OpenGL screenshots are fairly old, and don't seem to apply.
Thanks.
I wrote a class to work around this problem.
Basically you take directly a screenshot from the screen, and then if you want you can take just a part of the image and also scale it.
Taking a screenshot from the screen, you take every stuff. UIKit , OpenGL, AVFoundation, etc.
Here the class: https://github.com/matteogobbi/MGScreenshotHelper/
Below useful functions, but i suggest you to download (and star :D) directly my helper class ;)
/* Get the screenshot of the screen (useful when you have UIKit elements and OpenGL or AVFoundation stuff */
+ (UIImage *)screenshotFromScreen
{
CGImageRef UIGetScreenImage(void);
CGImageRef screen = UIGetScreenImage();
UIImage* screenImage = [UIImage imageWithCGImage:screen];
CGImageRelease(screen);
return screenImage;
}
/* Get the screenshot of a determinate rect of the screen, and scale it to the size that you want. */
+ (UIImage *)getScreenshotFromScreenWithRect:(CGRect)captureRect andScaleToSize:(CGSize)newSize
{
UIImage *image = [[self class] screenshotFromScreen];
image = [[self class] cropImage:image withRect:captureRect];
image = [[self class] scaleImage:image toSize:newSize];
return image;
}
#pragma mark - Other methods
/* Get a portion of an image */
+ (UIImage *)cropImage:(UIImage *)image withRect:(CGRect)rect
{
CGImageRef imageRef = CGImageCreateWithImageInRect([image CGImage], rect);
UIImage *cropedImage = [UIImage imageWithCGImage:imageRef];
return cropedImage;
}
/* Scale an image */
+ (UIImage *)scaleImage:(UIImage *)image toSize:(CGSize)newSize
{
UIGraphicsBeginImageContextWithOptions(newSize, YES, 0.0);
[image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return scaledImage;
}
Ok turns out this is a problem only in the Simulator. On a device it seems to work 98% of the time.
I am trying to convert an image into grayscale in the following way:
#define bytesPerPixel 4
#define bitsPerComponent 8
-(unsigned char*) getBytesForImage: (UIImage*)pImage
{
CGImageRef image = [pImage CGImage];
NSUInteger width = CGImageGetWidth(image);
NSUInteger height = CGImageGetHeight(image);
NSUInteger bytesPerRow = bytesPerPixel * width;
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
unsigned char *rawData = malloc(height * width * 4);
CGContextRef context = CGBitmapContextCreate(rawData, width, height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(context, CGRectMake(0, 0, width, height), image);
CGContextRelease(context);
return rawData;
}
-(UIImage*) processImage: (UIImage*)pImage
{
DebugLog(#"processing image");
unsigned char *rawData = [self getBytesForImage: pImage];
NSUInteger width = pImage.size.width;
NSUInteger height = pImage.size.height;
DebugLog(#"width: %d", width);
DebugLog(#"height: %d", height);
NSUInteger bytesPerRow = bytesPerPixel * width;
for (int xCoordinate = 0; xCoordinate < width; xCoordinate++)
{
for (int yCoordinate = 0; yCoordinate < height; yCoordinate++)
{
int byteIndex = (bytesPerRow * yCoordinate) + xCoordinate * bytesPerPixel;
//Getting original colors
float red = ( rawData[byteIndex] / 255.f );
float green = ( rawData[byteIndex + 1] / 255.f );
float blue = ( rawData[byteIndex + 2] / 255.f );
//Processing pixel data
float averageColor = (red + green + blue) / 3.0f;
red = averageColor;
green = averageColor;
blue = averageColor;
//Assigning new color components
rawData[byteIndex] = (unsigned char) red * 255;
rawData[byteIndex + 1] = (unsigned char) green * 255;
rawData[byteIndex + 2] = (unsigned char) blue * 255;
}
}
NSData* newPixelData = [NSData dataWithBytes: rawData length: height * width * 4];
UIImage* newImage = [UIImage imageWithData: newPixelData];
free(rawData);
DebugLog(#"image processed");
return newImage;
}
So when I want to convert an image I just call processImage:
imageToDisplay.image = [self processImage: image];
But imageToDisplay doesn't display. What may be the problem?
Thanks.
I needed a version that preserved the alpha channel, so I modified the code posted by Dutchie432:
#implementation UIImage (grayscale)
typedef enum {
ALPHA = 0,
BLUE = 1,
GREEN = 2,
RED = 3
} PIXELS;
- (UIImage *)convertToGrayscale {
CGSize size = [self size];
int width = size.width;
int height = size.height;
// the pixels will be painted to this array
uint32_t *pixels = (uint32_t *) malloc(width * height * sizeof(uint32_t));
// clear the pixels so any transparency is preserved
memset(pixels, 0, width * height * sizeof(uint32_t));
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
// create a context with RGBA pixels
CGContextRef context = CGBitmapContextCreate(pixels, width, height, 8, width * sizeof(uint32_t), colorSpace,
kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedLast);
// paint the bitmap to our context which will fill in the pixels array
CGContextDrawImage(context, CGRectMake(0, 0, width, height), [self CGImage]);
for(int y = 0; y < height; y++) {
for(int x = 0; x < width; x++) {
uint8_t *rgbaPixel = (uint8_t *) &pixels[y * width + x];
// convert to grayscale using recommended method: http://en.wikipedia.org/wiki/Grayscale#Converting_color_to_grayscale
uint32_t gray = 0.3 * rgbaPixel[RED] + 0.59 * rgbaPixel[GREEN] + 0.11 * rgbaPixel[BLUE];
// set the pixels to gray
rgbaPixel[RED] = gray;
rgbaPixel[GREEN] = gray;
rgbaPixel[BLUE] = gray;
}
}
// create a new CGImageRef from our context with the modified pixels
CGImageRef image = CGBitmapContextCreateImage(context);
// we're done with the context, color space, and pixels
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
free(pixels);
// make a new UIImage to return
UIImage *resultUIImage = [UIImage imageWithCGImage:image];
// we're done with image now too
CGImageRelease(image);
return resultUIImage;
}
#end
Here is a code using only UIKit and the luminosity blending mode. A bit of a hack, but it works well.
// Transform the image in grayscale.
- (UIImage*) grayishImage: (UIImage*) inputImage {
// Create a graphic context.
UIGraphicsBeginImageContextWithOptions(inputImage.size, YES, 1.0);
CGRect imageRect = CGRectMake(0, 0, inputImage.size.width, inputImage.size.height);
// Draw the image with the luminosity blend mode.
// On top of a white background, this will give a black and white image.
[inputImage drawInRect:imageRect blendMode:kCGBlendModeLuminosity alpha:1.0];
// Get the resulting image.
UIImage *filteredImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return filteredImage;
}
To keep the transparency, maybe you can just set the opaque mode parameter of the UIGraphicsBeginImageContextWithOptions to NO. Needs to be checked.
Based on Cam's code with the ability to deal with the scale for Retina displays.
- (UIImage *) toGrayscale
{
const int RED = 1;
const int GREEN = 2;
const int BLUE = 3;
// Create image rectangle with current image width/height
CGRect imageRect = CGRectMake(0, 0, self.size.width * self.scale, self.size.height * self.scale);
int width = imageRect.size.width;
int height = imageRect.size.height;
// the pixels will be painted to this array
uint32_t *pixels = (uint32_t *) malloc(width * height * sizeof(uint32_t));
// clear the pixels so any transparency is preserved
memset(pixels, 0, width * height * sizeof(uint32_t));
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
// create a context with RGBA pixels
CGContextRef context = CGBitmapContextCreate(pixels, width, height, 8, width * sizeof(uint32_t), colorSpace,
kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedLast);
// paint the bitmap to our context which will fill in the pixels array
CGContextDrawImage(context, CGRectMake(0, 0, width, height), [self CGImage]);
for(int y = 0; y < height; y++) {
for(int x = 0; x < width; x++) {
uint8_t *rgbaPixel = (uint8_t *) &pixels[y * width + x];
// convert to grayscale using recommended method: http://en.wikipedia.org/wiki/Grayscale#Converting_color_to_grayscale
uint8_t gray = (uint8_t) ((30 * rgbaPixel[RED] + 59 * rgbaPixel[GREEN] + 11 * rgbaPixel[BLUE]) / 100);
// set the pixels to gray
rgbaPixel[RED] = gray;
rgbaPixel[GREEN] = gray;
rgbaPixel[BLUE] = gray;
}
}
// create a new CGImageRef from our context with the modified pixels
CGImageRef image = CGBitmapContextCreateImage(context);
// we're done with the context, color space, and pixels
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
free(pixels);
// make a new UIImage to return
UIImage *resultUIImage = [UIImage imageWithCGImage:image
scale:self.scale
orientation:UIImageOrientationUp];
// we're done with image now too
CGImageRelease(image);
return resultUIImage;
}
I liked Mathieu Godart's answer, but it didn't seem to work properly for retina or alpha images. Here's an updated version that seems to work for both of those for me:
- (UIImage*)convertToGrayscale
{
UIGraphicsBeginImageContextWithOptions(self.size, NO, self.scale);
CGRect imageRect = CGRectMake(0.0f, 0.0f, self.size.width, self.size.height);
CGContextRef ctx = UIGraphicsGetCurrentContext();
// Draw a white background
CGContextSetRGBFillColor(ctx, 1.0f, 1.0f, 1.0f, 1.0f);
CGContextFillRect(ctx, imageRect);
// Draw the luminosity on top of the white background to get grayscale
[self drawInRect:imageRect blendMode:kCGBlendModeLuminosity alpha:1.0f];
// Apply the source image's alpha
[self drawInRect:imageRect blendMode:kCGBlendModeDestinationIn alpha:1.0f];
UIImage* grayscaleImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return grayscaleImage;
}
What exactly takes place when you use this function? Is the function returning an invalid image, or is the display not showing it correctly?
This is the method I use to convert to greyscale.
- (UIImage *) convertToGreyscale:(UIImage *)i {
int kRed = 1;
int kGreen = 2;
int kBlue = 4;
int colors = kGreen | kBlue | kRed;
int m_width = i.size.width;
int m_height = i.size.height;
uint32_t *rgbImage = (uint32_t *) malloc(m_width * m_height * sizeof(uint32_t));
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(rgbImage, m_width, m_height, 8, m_width * 4, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast);
CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
CGContextSetShouldAntialias(context, NO);
CGContextDrawImage(context, CGRectMake(0, 0, m_width, m_height), [i CGImage]);
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
// now convert to grayscale
uint8_t *m_imageData = (uint8_t *) malloc(m_width * m_height);
for(int y = 0; y < m_height; y++) {
for(int x = 0; x < m_width; x++) {
uint32_t rgbPixel=rgbImage[y*m_width+x];
uint32_t sum=0,count=0;
if (colors & kRed) {sum += (rgbPixel>>24)&255; count++;}
if (colors & kGreen) {sum += (rgbPixel>>16)&255; count++;}
if (colors & kBlue) {sum += (rgbPixel>>8)&255; count++;}
m_imageData[y*m_width+x]=sum/count;
}
}
free(rgbImage);
// convert from a gray scale image back into a UIImage
uint8_t *result = (uint8_t *) calloc(m_width * m_height *sizeof(uint32_t), 1);
// process the image back to rgb
for(int i = 0; i < m_height * m_width; i++) {
result[i*4]=0;
int val=m_imageData[i];
result[i*4+1]=val;
result[i*4+2]=val;
result[i*4+3]=val;
}
// create a UIImage
colorSpace = CGColorSpaceCreateDeviceRGB();
context = CGBitmapContextCreate(result, m_width, m_height, 8, m_width * sizeof(uint32_t), colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast);
CGImageRef image = CGBitmapContextCreateImage(context);
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
UIImage *resultUIImage = [UIImage imageWithCGImage:image];
CGImageRelease(image);
free(m_imageData);
// make sure the data will be released by giving it to an autoreleased NSData
[NSData dataWithBytesNoCopy:result length:m_width * m_height];
return resultUIImage;
}
Different approach with CIFilter. Preserves alpha channel and works with transparent background:
+ (UIImage *)convertImageToGrayScale:(UIImage *)image
{
CIImage *inputImage = [CIImage imageWithCGImage:image.CGImage];
CIContext *context = [CIContext contextWithOptions:nil];
CIFilter *filter = [CIFilter filterWithName:#"CIColorControls"];
[filter setValue:inputImage forKey:kCIInputImageKey];
[filter setValue:#(0.0) forKey:kCIInputSaturationKey];
CIImage *outputImage = filter.outputImage;
CGImageRef cgImageRef = [context createCGImage:outputImage fromRect:outputImage.extent];
UIImage *result = [UIImage imageWithCGImage:cgImageRef];
CGImageRelease(cgImageRef);
return result;
}
A swift extension to UIImage, preserving alpha:
extension UIImage {
private func convertToGrayScaleNoAlpha() -> CGImageRef {
let colorSpace = CGColorSpaceCreateDeviceGray();
let bitmapInfo = CGBitmapInfo(CGImageAlphaInfo.None.rawValue)
let context = CGBitmapContextCreate(nil, UInt(size.width), UInt(size.height), 8, 0, colorSpace, bitmapInfo)
CGContextDrawImage(context, CGRectMake(0, 0, size.width, size.height), self.CGImage)
return CGBitmapContextCreateImage(context)
}
/**
Return a new image in shades of gray + alpha
*/
func convertToGrayScale() -> UIImage {
let bitmapInfo = CGBitmapInfo(CGImageAlphaInfo.Only.rawValue)
let context = CGBitmapContextCreate(nil, UInt(size.width), UInt(size.height), 8, 0, nil, bitmapInfo)
CGContextDrawImage(context, CGRectMake(0, 0, size.width, size.height), self.CGImage);
let mask = CGBitmapContextCreateImage(context)
return UIImage(CGImage: CGImageCreateWithMask(convertToGrayScaleNoAlpha(), mask), scale: scale, orientation:imageOrientation)!
}
}
Here is another good solution as a category method on UIImage. It's based on this blog post and its comments. But I fixed a memory issue here:
- (UIImage *)grayScaleImage {
// Create image rectangle with current image width/height
CGRect imageRect = CGRectMake(0, 0, self.size.width * self.scale, self.size.height * self.scale);
// Grayscale color space
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
// Create bitmap content with current image size and grayscale colorspace
CGContextRef context = CGBitmapContextCreate(nil, self.size.width * self.scale, self.size.height * self.scale, 8, 0, colorSpace, kCGImageAlphaNone);
// Draw image into current context, with specified rectangle
// using previously defined context (with grayscale colorspace)
CGContextDrawImage(context, imageRect, [self CGImage]);
// Create bitmap image info from pixel data in current context
CGImageRef grayImage = CGBitmapContextCreateImage(context);
// release the colorspace and graphics context
CGColorSpaceRelease(colorSpace);
CGContextRelease(context);
// make a new alpha-only graphics context
context = CGBitmapContextCreate(nil, self.size.width * self.scale, self.size.height * self.scale, 8, 0, nil, kCGImageAlphaOnly);
// draw image into context with no colorspace
CGContextDrawImage(context, imageRect, [self CGImage]);
// create alpha bitmap mask from current context
CGImageRef mask = CGBitmapContextCreateImage(context);
// release graphics context
CGContextRelease(context);
// make UIImage from grayscale image with alpha mask
CGImageRef cgImage = CGImageCreateWithMask(grayImage, mask);
UIImage *grayScaleImage = [UIImage imageWithCGImage:cgImage scale:self.scale orientation:self.imageOrientation];
// release the CG images
CGImageRelease(cgImage);
CGImageRelease(grayImage);
CGImageRelease(mask);
// return the new grayscale image
return grayScaleImage;
}
An fast and efficient Swift 3 implementation for iOS 9/10. I feel this is efficient having now tried every image filtering method I could find for processing 100's of images at a time (when downloading using AlamofireImage's ImageFilter option). I settled on this method as FAR better than any other I tried (for my use case) in terms of memory and speed.
func convertToGrayscale() -> UIImage? {
UIGraphicsBeginImageContextWithOptions(self.size, false, self.scale)
let imageRect = CGRect(x: 0.0, y: 0.0, width: self.size.width, height: self.size.height)
let context = UIGraphicsGetCurrentContext()
// Draw a white background
context!.setFillColor(red: 1.0, green: 1.0, blue: 1.0, alpha: 1.0)
context!.fill(imageRect)
// optional: increase contrast with colorDodge before applying luminosity
// (my images were too dark when using just luminosity - you may not need this)
self.draw(in: imageRect, blendMode: CGBlendMode.colorDodge, alpha: 0.7)
// Draw the luminosity on top of the white background to get grayscale of original image
self.draw(in: imageRect, blendMode: CGBlendMode.luminosity, alpha: 0.90)
// optional: re-apply alpha if your image has transparency - based on user1978534's answer (I haven't tested this as I didn't have transparency - I just know this would be the the syntax)
// self.draw(in: imageRect, blendMode: CGBlendMode.destinationIn, alpha: 1.0)
let grayscaleImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return grayscaleImage
}
Re the use of colorDodge: I initially had issues getting my images light enough to match the grayscale coloring produced by using CIFilter("CIPhotoEffectTonal") - my results turned out too dark. I was able to get a decent match by applying CGBlendMode.colorDodge # ~ 0.7 alpha, which seems to increase the overall contrast.
Other color blend effects might work too - but I think you would want to apply before luminocity, which is the greyscale filtering effect. I found this page very helpful to reference about the different BlendModes.
Re efficiency gains I found: I need to process 100's of thumbnail images as they are loaded from a server (using AlamofireImage for async loading, caching, and applying a filter). I started to experience crashes when the total size of my images exceeded the cache size, so I experimented with other methods.
The CoreImage CPU based CIFilter approach was the first I tried, and wasn't memory efficient enough for the number of images I'm handling.
I also tried applying a CIFilter via the GPU using EAGLContext(api: .openGLES3), which was actually even more memory intensive - I actually got memory warnings for 450+ mb use while loading 200 + images.
I tried bitmap processing (i.e. CGContext(data: nil, width: width, height: height, bitsPerComponent: 8, bytesPerRow: 0, space: colorSpace, bitmapInfo: CGImageAlphaInfo.none.rawValue)... which worked well except I couldn't get a high enough resolution for a modern retina device. Images were very grainy even when I added context.scaleBy(x: scaleFactor, y: scaleFactor).
So out of everything I tried, this method (UIGraphics Context Draw) to be VASTLY more efficient re speed and memory when applying as a filter to AlamofireImage. As in, seeing less than 70 mbs ram when processing my 200+ images and them basically loading instantly, rather than over about 35 seconds it took with the openEAGL methods. I know these are not very scientific benchmarks. I will instrument it if anyone is very curious though :)
And lastly, if you do need to pass this or another greyscale filter into AlamofireImage - this is how to do it: (note you must import AlamofireImage into your class to use ImageFilter)
public struct GrayScaleFilter: ImageFilter {
public init() {
}
public var filter: (UIImage) -> UIImage {
return { image in
return image.convertToGrayscale() ?? image
}
}
}
To use it, create the filter like this and pass into af_setImage like so:
let filter = GrayScaleFilter()
imageView.af_setImage(withURL: url, filter: filter)
#interface UIImageView (Settings)
- (void)convertImageToGrayScale;
#end
#implementation UIImageView (Settings)
- (void)convertImageToGrayScale
{
// Create image rectangle with current image width/height
CGRect imageRect = CGRectMake(0, 0, self.image.size.width, self.image.size.height);
// Grayscale color space
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
// Create bitmap content with current image size and grayscale colorspace
CGContextRef context = CGBitmapContextCreate(nil, self.image.size.width, self.image.size.height, 8, 0, colorSpace, kCGImageAlphaNone);
// Draw image into current context, with specified rectangle
// using previously defined context (with grayscale colorspace)
CGContextDrawImage(context, imageRect, [self.image CGImage]);
// Create bitmap image info from pixel data in current context
CGImageRef imageRef = CGBitmapContextCreateImage(context);
// Create a new UIImage object
UIImage *newImage = [UIImage imageWithCGImage:imageRef];
// Release colorspace, context and bitmap information
CGColorSpaceRelease(colorSpace);
CGContextRelease(context);
CFRelease(imageRef);
// Return the new grayscale image
self.image = newImage;
}
#end
I have yet another answer. This one is extremely performant and handles retina graphics as well as transparency. It expands on Sargis Gevorgyan's approach:
+ (UIImage*) grayScaleFromImage:(UIImage*)image opaque:(BOOL)opaque
{
// NSTimeInterval start = [NSDate timeIntervalSinceReferenceDate];
CGSize size = image.size;
CGRect bounds = CGRectMake(0, 0, size.width, size.height);
// Create bitmap content with current image size and grayscale colorspace
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
size_t bitsPerComponent = 8;
size_t bytesPerPixel = opaque ? 1 : 2;
size_t bytesPerRow = bytesPerPixel * size.width * image.scale;
CGContextRef context = CGBitmapContextCreate(nil, size.width, size.height, bitsPerComponent, bytesPerRow, colorSpace, opaque ? kCGImageAlphaNone : kCGImageAlphaPremultipliedLast);
// create image from bitmap
CGContextDrawImage(context, bounds, image.CGImage);
CGImageRef cgImage = CGBitmapContextCreateImage(context);
UIImage* result = [[UIImage alloc] initWithCGImage:cgImage scale:image.scale orientation:UIImageOrientationUp];
CGImageRelease(cgImage);
CGContextRelease(context);
// performance results on iPhone 6S+ in Release mode.
// Results are in photo pixels, not device pixels:
// ~ 5ms for 500px x 600px
// ~ 15ms for 2200px x 600px
// NSLog(#"generating %d x %d # %dx grayscale took %f seconds", (int)size.width, (int)size.height, (int)image.scale, [NSDate timeIntervalSinceReferenceDate] - start);
return result;
}
Using blending modes instead is elegant, but copying to a grayscale bitmap is more performant because you only use one or two color channels instead of four. The opacity bool is meant to take in your UIView's opaque flag so you can opt out of using an alpha channel if you know you won't need one.
I haven't tried the Core Image based solutions in this answer thread, but I would be very cautious about using Core Image if performance is important.
Thats my try to convert fast by drawing directly to grayscale colorspace without each pixel enumeration. It works 10x faster than CIImageFilter solutions.
#implementation UIImage (Grayscale)
static UIImage *grayscaleImageFromCIImage(CIImage *image, CGFloat scale)
{
CIImage *blackAndWhite = [CIFilter filterWithName:#"CIColorControls" keysAndValues:kCIInputImageKey, image, kCIInputBrightnessKey, #0.0, kCIInputContrastKey, #1.1, kCIInputSaturationKey, #0.0, nil].outputImage;
CIImage *output = [CIFilter filterWithName:#"CIExposureAdjust" keysAndValues:kCIInputImageKey, blackAndWhite, kCIInputEVKey, #0.7, nil].outputImage;
CGImageRef ref = [[CIContext contextWithOptions:nil] createCGImage:output fromRect:output.extent];
UIImage *result = [UIImage imageWithCGImage:ref scale:scale orientation:UIImageOrientationUp];
CGImageRelease(ref);
return result;
}
static UIImage *grayscaleImageFromCGImage(CGImageRef imageRef, CGFloat scale)
{
NSInteger width = CGImageGetWidth(imageRef) * scale;
NSInteger height = CGImageGetHeight(imageRef) * scale;
NSMutableData *pixels = [NSMutableData dataWithLength:width*height];
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
CGContextRef context = CGBitmapContextCreate(pixels.mutableBytes, width, height, 8, width, colorSpace, 0);
CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
CGImageRef ref = CGBitmapContextCreateImage(context);
UIImage *result = [UIImage imageWithCGImage:ref scale:scale orientation:UIImageOrientationUp];
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
CGImageRelease(ref);
return result;
}
- (UIImage *)grayscaleImage
{
if (self.CIImage) {
return grayscaleImageFromCIImage(self.CIImage, self.scale);
} else if (self.CGImage) {
return grayscaleImageFromCGImage(self.CGImage, self.scale);
}
return nil;
}
#end
Yes, I know this sounds like a duplicate... but I've tried lots of examples and even Apple's official code on their developer page and this is resulting in a white image on iPhone 4S & iPad 3.
Works great on iPad 1 and the iPhone Simulator though.
width and height passed to convertBitmapRGBA8ToUIImage is in actual pixels, not UIKit 'points'. I.e., on iPad 1, it would be 1024, 768. On iPad 3, it's 2048, 1536.
The raw data buffer is RGBA data read from glReadPixels and flipped manually before passing to tweetMessage().
- (UIImage *) convertBitmapRGBA8ToUIImage:(unsigned char *) buffer
withWidth:(int) width
withHeight:(int) height {
CGDataProviderRef ref = CGDataProviderCreateWithData(NULL, buffer, width * height * 4, NULL);
CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
CGImageRef iref = CGImageCreate(width, height, 8, 32, width * 4, colorspace, kCGBitmapByteOrder32Big | kCGImageAlphaPremultipliedLast, ref, NULL, true, kCGRenderingIntentDefault);
float scale = 1.0f;
if ([[UIScreen mainScreen] respondsToSelector:#selector(scale)])
{
scale = [[UIScreen mainScreen] scale];
}
UIGraphicsBeginImageContextWithOptions(CGSizeMake(width/scale, height/scale), NO, scale);
CGContextRef cgcontext = UIGraphicsGetCurrentContext();
CGContextSetBlendMode(cgcontext, kCGBlendModeCopy);
// Image needs to be flipped BACK for CG
CGContextTranslateCTM(cgcontext, 0, height/scale);
CGContextScaleCTM(cgcontext, 1, -1);
CGContextDrawImage(cgcontext, CGRectMake(0.0, 0.0, width/scale, height/scale), iref);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
CFRelease(ref);
CFRelease(colorspace);
CGImageRelease(iref);
return image;
}
- (void)tweetMessage:(const char *)message withURL:(const char *)url withImage:(unsigned char*)rawRGBAImage withWidth:(unsigned int)imageWidth withHeight:(unsigned int)imageHeight
{
UIImage *tweetImage = nil;
if (rawRGBAImage != nil)
{
// Convert raw data to UIImage
tweetImage = [self convertBitmapRGBA8ToUIImage:rawRGBAImage withWidth:imageWidth withHeight:imageHeight];
}
}
I have UITableViewCell with image in the right size.
This is how the cell should look like:
And i have the backgound:
And the image placeholder:
And i want to know if there is a way to crop image with the iOS library?
Yes that possible:
UIImage *imageToCrop = ...;
UIGraphicsBeginImageContext();
CGContextRef context = UIGraphicsGetCurrentContext();
[imageToCrop drawAtPoint:CGPointZero];
CGContextAddEllipseInRect(context, CGRectMake(0 ,0, imageToCrop.size.width, imageToCrop.size.height);
CGContextClip(context);
UIImage *croppedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
You can use CoreGraphics to add mask or clip with path. Mask is image with alpha channel which determines what part of image show. Below example how clip with image mask:
- (UIImage *)croppedImage:(UIImage *)sourceImage
{
UIGraphicsBeginImageContextWithOptions(CGSizeMake(width, height), NO, [UIScreen mainScreen].scale);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextClipToMask(context, CGRectMake(0, 0, width, height), [UIImage imageNamed:#"mask"].CGImage);
[sourceImage drawInRect:CGRectMake(0, 0, width, height)];
UIImage *resultImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return resultImage;
}
Then you can write cell.picture = [self croppedImage:sourceImage];
You can use image masking technique to crop this image
Please have a look at this link
https://developer.apple.com/library/mac/documentation/graphicsimaging/conceptual/drawingwithquartz2d/dq_images/dq_images.html#//apple_ref/doc/uid/TP30001066-CH212-CJBHIJEB
I have written some code that may help you out
#interface ImageRenderer : NSObject {
UIImage *image_;
}
#property (nonatomic, retain) UIImage * image;
- (void)cropImageinRect:(CGRect)rect;
- (void)maskImageWithMask:(UIImage *)maskImage;
- (void)imageWithAlpha;
#end
#implementation ImageRenderer
#synthesize image = image_;
- (void)cropImageinRect:(CGRect)rect {
CGImageRef imageRef = CGImageCreateWithImageInRect(image_.CGImage, rect);
image_ = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
}
- (void)maskImageWithMask:(UIImage *)maskImage {
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGImageRef maskImageRef = [maskImage CGImage];
// create a bitmap graphics context the size of the image
CGContextRef mainViewContentContext = CGBitmapContextCreate (NULL, maskImage.size.width, maskImage.size.height, 8, 0, colorSpace, kCGImageAlphaPremultipliedLast);
if (mainViewContentContext == NULL){
return;
}
CGFloat ratio = 0;
ratio = maskImage.size.width/ image_.size.width;
if(ratio * image_.size.height < maskImage.size.height) {
ratio = maskImage.size.height/ image_.size.height;
}
CGRect rect1 = {{0, 0}, {maskImage.size.width, maskImage.size.height}};
CGRect rect2 = {{-((image_.size.width*ratio)-maskImage.size.width)/2 , -((image_.size.height*ratio)-maskImage.size.height)/2}, {image_.size.width*ratio, image_.size.height*ratio}};
CGContextClipToMask(mainViewContentContext, rect1, maskImageRef);
CGContextDrawImage(mainViewContentContext, rect2, image_.CGImage);
// Create CGImageRef of the main view bitmap content, and then
// release that bitmap context
CGImageRef newImage = CGBitmapContextCreateImage(mainViewContentContext);
CGContextRelease(mainViewContentContext);
image_ = [UIImage imageWithCGImage:newImage];
CGImageRelease(newImage);
}
- (void)imageWithAlpha {
CGImageRef imageRef = image_.CGImage;
CGFloat width = CGImageGetWidth(imageRef);
CGFloat height = CGImageGetHeight(imageRef);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(nil, width, height, 8, 0, colorSpace, kCGImageAlphaPremultipliedFirst);
CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
CGImageRef resultImageRef = CGBitmapContextCreateImage(context);
image_ = [UIImage imageWithCGImage:resultImageRef scale:image_.scale orientation:image_.imageOrientation];
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
CGImageRelease(resultImageRef);
}
#end
In this code you can crop the image out of a bigger one and then you can use a mask image to get your work done.