在我的iPhone应用程序上，我有一个UIImage实例。我想得到一个UIImage，它是第一个UIImage的结果，其中一个颜色（例如品红色）变得透明。我怎么能这样做？
答案 0 :(得分：32)
行。经过尝试我不知道这些解决方案有多少个版本，我有自己的定制版本。我发现@yubenyi的解决方案效果很好，但是如果你想从他的changeWhiteColorTransparent（）函数中获取输出并将其传回来，它就不起作用了。
我的第一步是将其功能更改为接受特定的颜色和容差，以便调用者可以指定一系列颜色以使其透明。这很好，几乎没有变化，但我发现输出不是一个有效的图像，用于传递具有第二个颜色范围的相同代码。
经过大量的反复试验，我通过自己进行颜色替换来实现这一目标。我拒绝这一点，因为当有API来做这件事时似乎太辛苦了，但它们并不总是按照你想要的方式行事。具体来说，CGImageCreateWithMaskingColors（）的输出不能用作对同一函数的另一个调用的输入。我无法找出原因，但我认为这与alpha通道有关。
无论如何，我的解决方案是：
- (UIImage*) replaceColor:(UIColor*)color inImage:(UIImage*)image withTolerance:(float)tolerance {
CGImageRef imageRef = [image CGImage];
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
NSUInteger bitmapByteCount = bytesPerRow * height;
unsigned char *rawData = (unsigned char*) calloc(bitmapByteCount, sizeof(unsigned char));
CGContextRef context = CGBitmapContextCreate(rawData, width, height,
bitsPerComponent, bytesPerRow, colorSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
CGColorRef cgColor = [color CGColor];
const CGFloat *components = CGColorGetComponents(cgColor);
float r = components[0];
float g = components[1];
float b = components[2];
//float a = components[3]; // not needed
r = r * 255.0;
g = g * 255.0;
b = b * 255.0;
const float redRange[2] = {
MAX(r - (tolerance / 2.0), 0.0),
MIN(r + (tolerance / 2.0), 255.0)
};
const float greenRange[2] = {
MAX(g - (tolerance / 2.0), 0.0),
MIN(g + (tolerance / 2.0), 255.0)
};
const float blueRange[2] = {
MAX(b - (tolerance / 2.0), 0.0),
MIN(b + (tolerance / 2.0), 255.0)
};
int byteIndex = 0;
while (byteIndex < bitmapByteCount) {
unsigned char red = rawData[byteIndex];
unsigned char green = rawData[byteIndex + 1];
unsigned char blue = rawData[byteIndex + 2];
if (((red >= redRange[0]) && (red <= redRange[1])) &&
((green >= greenRange[0]) && (green <= greenRange[1])) &&
((blue >= blueRange[0]) && (blue <= blueRange[1]))) {
// make the pixel transparent
//
rawData[byteIndex] = 0;
rawData[byteIndex + 1] = 0;
rawData[byteIndex + 2] = 0;
rawData[byteIndex + 3] = 0;
}
byteIndex += 4;
}
CGImageRef imgref = CGBitmapContextCreateImage(context);
UIImage *result = [UIImage imageWithCGImage:imgref];
CGImageRelease(imgref);
CGContextRelease(context);
free(rawData);
return result;
}
答案 1 :(得分：17)
这是对yubenyi的代码的调整，可以使用多次传递。它在处理之前通过将图像转换为未压缩的jpeg来剥离alpha通道。还添加了一些关于颜色范围选择如何工作的评论。
-(UIImage *)changeWhiteColorTransparent: (UIImage *)image
{
//convert to uncompressed jpg to remove any alpha channels
//this is a necessary first step when processing images that already have transparency
image = [UIImage imageWithData:UIImageJPEGRepresentation(image, 1.0)];
CGImageRef rawImageRef=image.CGImage;
//RGB color range to mask (make transparent) R-Low, R-High, G-Low, G-High, B-Low, B-High
const double colorMasking[6] = {222, 255, 222, 255, 222, 255};
UIGraphicsBeginImageContext(image.size);
CGImageRef maskedImageRef=CGImageCreateWithMaskingColors(rawImageRef, colorMasking);
//iPhone translation
CGContextTranslateCTM(UIGraphicsGetCurrentContext(), 0.0, image.size.height);
CGContextScaleCTM(UIGraphicsGetCurrentContext(), 1.0, -1.0);
CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, image.size.width, image.size.height), maskedImageRef);
UIImage *result = UIGraphicsGetImageFromCurrentImageContext();
CGImageRelease(maskedImageRef);
UIGraphicsEndImageContext();
return result;
}
答案 2 :(得分：12)
-(void)changeColor
{
UIImage *temp23=[UIImage imageNamed:@"leaf.png"];
CGImageRef ref1=[self createMask:temp23];
const float colorMasking[6] = {1.0, 2.0, 1.0, 1.0, 1.0, 1.0};
CGImageRef New=CGImageCreateWithMaskingColors(ref1, colorMasking);
UIImage *resultedimage=[UIImage imageWithCGImage:New];
}
-(CGImageRef)createMask:(UIImage*)temp
{
CGImageRef ref=temp.CGImage;
int mWidth=CGImageGetWidth(ref);
int mHeight=CGImageGetHeight(ref);
int count=mWidth*mHeight*4;
void *bufferdata=malloc(count);
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
CGContextRef cgctx = CGBitmapContextCreate (bufferdata,mWidth,mHeight, 8,mWidth*4, colorSpaceRef, kCGImageAlphaPremultipliedFirst);
CGRect rect = {0,0,mWidth,mHeight};
CGContextDrawImage(cgctx, rect, ref);
bufferdata = CGBitmapContextGetData (cgctx);
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, bufferdata, mWidth*mHeight*4, NULL);
CGImageRef savedimageref = CGImageCreate(mWidth,mHeight, 8, 32, mWidth*4, colorSpaceRef, bitmapInfo,provider , NULL, NO, renderingIntent);
CFRelease(colorSpaceRef);
return savedimageref;
}
上面的代码经过测试，我使用遮罩
将绿色更改为红色答案 3 :(得分：11)
这个功能可以工作！
-(UIImage *)changeWhiteColorTransparent: (UIImage *)image
{
CGImageRef rawImageRef=image.CGImage;
const float colorMasking[6] = {222, 255, 222, 255, 222, 255};
UIGraphicsBeginImageContext(image.size);
CGImageRef maskedImageRef=CGImageCreateWithMaskingColors(rawImageRef, colorMasking);
{
//if in iphone
CGContextTranslateCTM(UIGraphicsGetCurrentContext(), 0.0, image.size.height);
CGContextScaleCTM(UIGraphicsGetCurrentContext(), 1.0, -1.0);
}
CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, image.size.width, image.size.height), maskedImageRef);
UIImage *result = UIGraphicsGetImageFromCurrentImageContext();
CGImageRelease(maskedImageRef);
UIGraphicsEndImageContext();
return result;
}
答案 4 :(得分：10)
使用你的功能之后，我发现了更简单的为UIImage制作透明背景的方法：）
例如，您有带黑色背景的PNG图像，并且您希望在屏幕上使此背景透明。
你可以试试这个：
UIImage * image = [UIImage imageNamed:@"image.png"];
const CGFloat colorMasking[6] = {0.0, 0.0, 0.0, 0.0, 0.0, 0.0};
image = [UIImage imageWithCGImage: CGImageCreateWithMaskingColors(image.CGImage, colorMasking)];
你有透明背景的图像。
这就是全部：）
答案 5 :(得分：5)
Swift 4 :(用于白色遮蔽）
extension UIImage {
func imageByMakingWhiteBackgroundTransparent() -> UIImage? {
let image = UIImage(data: UIImageJPEGRepresentation(self, 1.0)!)!
let rawImageRef: CGImage = image.cgImage!
let colorMasking: [CGFloat] = [222, 255, 222, 255, 222, 255]
UIGraphicsBeginImageContext(image.size);
let maskedImageRef = rawImageRef.copy(maskingColorComponents: colorMasking)
UIGraphicsGetCurrentContext()?.translateBy(x: 0.0,y: image.size.height)
UIGraphicsGetCurrentContext()?.scaleBy(x: 1.0, y: -1.0)
UIGraphicsGetCurrentContext()?.draw(maskedImageRef!, in: CGRect.init(x: 0, y: 0, width: image.size.width, height: image.size.height))
let result = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return result
}
}
答案 6 :(得分：2)
基于@ PKCLsoft 的高超答案，我进行了一次编辑，它只使白色透明，但它根据＆＃34; white＆＃34;像素是。当您尝试使用黑白图像制作蒙版时，这可能会非常方便，因此它会在文本或形状上提供平滑的边缘。
- (UIImage *)makeWhiteColorTransparentInImage:(UIImage *)image {
CGImageRef imageRef = [image CGImage];
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
NSUInteger bitmapByteCount = bytesPerRow * height;
unsigned char *rawData = (unsigned char*) calloc(bitmapByteCount, sizeof(unsigned char));
CGContextRef context = CGBitmapContextCreate(rawData, width, height,
bitsPerComponent, bytesPerRow, colorSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
int byteIndex = 0;
while (byteIndex < bitmapByteCount) {
unsigned char red = rawData[byteIndex];
unsigned char green = rawData[byteIndex + 1];
unsigned char blue = rawData[byteIndex + 2];
unsigned char alpha = rawData[byteIndex + 3];
if (alpha == 0.0) {
rawData[byteIndex + 3] = 0.0;
} else {
rawData[byteIndex + 3] = 255.0 - (red + green + blue) / 3.0;
}
byteIndex += 4;
}
CGImageRef imgref = CGBitmapContextCreateImage(context);
UIImage *result = [UIImage imageWithCGImage:imgref];
CGImageRelease(imgref);
CGContextRelease(context);
free(rawData);
return result;
}
我希望有一天能帮到某人：）
答案 7 :(得分：1)
从白色背景色到透明色的快速版本
extension UIImage {
func imageByMakingWhiteBackgroundTransparent() -> UIImage? {
let image = UIImage(data: self.jpegData(compressionQuality: 1.0)!)!
let rawImageRef: CGImage = image.cgImage!
let colorMasking: [CGFloat] = [222, 255, 222, 255, 222, 255]
UIGraphicsBeginImageContext(image.size);
let maskedImageRef = rawImageRef.copy(maskingColorComponents: colorMasking)
UIGraphicsGetCurrentContext()?.translateBy(x: 0.0,y: image.size.height)
UIGraphicsGetCurrentContext()?.scaleBy(x: 1.0, y: -1.0)
UIGraphicsGetCurrentContext()?.draw(maskedImageRef!, in: CGRect.init(x: 0, y: 0, width: image.size.width, height: image.size.height))
let result = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return result
}
}
答案 8 :(得分：0)
我自己从未做过这样的事情，但看起来CGImageCreateWithMaskingColors似乎可以在这里使用。但是，使用Core Graphics超出了我在本网站的答案中可以解释的范围;查看您的文档并在Web上搜索教程。
答案 9 :(得分：0)
swift 5中的UIImage扩展，可以将任何颜色更改为透明。基于@fegoulart答案。
extension UIImage {
func remove(color: UIColor) -> UIImage? {
let cgColor = color.cgColor
let components = cgColor.components
var r = components?[0] ?? 0.0
var g = components?[1] ?? 0.0
var b = components?[2] ?? 0.0
r = r * 255.0
g = g * 255.0
b = b * 255.0
let colorMasking: [CGFloat] = [r, r, g, g, b, b]
let image = UIImage(data: self.jpegData(compressionQuality: 1.0)!)!
let rawImageRef: CGImage = image.cgImage!
UIGraphicsBeginImageContext(image.size);
let maskedImageRef = rawImageRef.copy(maskingColorComponents: colorMasking)
UIGraphicsGetCurrentContext()?.translateBy(x: 0.0,y: image.size.height)
UIGraphicsGetCurrentContext()?.scaleBy(x: 1.0, y: -1.0)
UIGraphicsGetCurrentContext()?.draw(maskedImageRef!, in: CGRect.init(x: 0, y: 0, width: image.size.width, height: image.size.height))
let result = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return result
}
}