我有一个 UIImage (Cocoa Touch)。从那，我很高兴得到一个 CGImage 或任何你想要的东西。我想写这个函数：
- (int)getRGBAFromImage:(UIImage *)image atX:(int)xx andY:(int)yy {
// [...]
// What do I want to read about to help
// me fill in this bit, here?
// [...]
int result = (red << 24) | (green << 16) | (blue << 8) | alpha;
return result;
}
仅供参考，我将 Keremk 的答案与我的原始大纲结合起来，清理了拼写错误，将其概括为返回一组颜色并编译整个内容。结果如下：
+ (NSArray*)getRGBAsFromImage:(UIImage*)image atX:(int)x andY:(int)y count:(int)count
{
NSMutableArray *result = [NSMutableArray arrayWithCapacity:count];
// First get the image into your data buffer
CGImageRef imageRef = [image CGImage];
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
unsigned char *rawData = (unsigned char*) calloc(height * width * 4, sizeof(unsigned char));
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(rawData, width, height,
bitsPerComponent, bytesPerRow, colorSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
CGContextRelease(context);
// Now your rawData contains the image data in the RGBA8888 pixel format.
NSUInteger byteIndex = (bytesPerRow * y) + x * bytesPerPixel;
for (int i = 0 ; i < count ; ++i)
{
CGFloat alpha = ((CGFloat) rawData[byteIndex + 3] ) / 255.0f;
CGFloat red = ((CGFloat) rawData[byteIndex] ) / alpha;
CGFloat green = ((CGFloat) rawData[byteIndex + 1] ) / alpha;
CGFloat blue = ((CGFloat) rawData[byteIndex + 2] ) / alpha;
byteIndex += bytesPerPixel;
UIColor *acolor = [UIColor colorWithRed:red green:green blue:blue alpha:alpha];
[result addObject:acolor];
}
free(rawData);
return result;
}
一种方法是将图像绘制到由给定颜色空间的给定缓冲区支持的位图上下文（在本例中为 RGB）：（请注意，这会将图像数据复制到该缓冲区，所以你这样做想要缓存它而不是每次需要获取像素值时都执行此操作）
请参见下面的示例：
// First get the image into your data buffer
CGImageRef image = [myUIImage CGImage];
NSUInteger width = CGImageGetWidth(image);
NSUInteger height = CGImageGetHeight(image);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
unsigned char *rawData = malloc(height * width * 4);
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(rawData, width, height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(context, CGRectMake(0, 0, width, height));
CGContextRelease(context);
// Now your rawData contains the image data in the RGBA8888 pixel format.
int byteIndex = (bytesPerRow * yy) + xx * bytesPerPixel;
red = rawData[byteIndex];
green = rawData[byteIndex + 1];
blue = rawData[byteIndex + 2];
alpha = rawData[byteIndex + 3];
Apple 的技术问答 QA1509展示了以下简单方法：
CFDataRef CopyImagePixels(CGImageRef inImage)
{
return CGDataProviderCopyData(CGImageGetDataProvider(inImage));
}
用于CFDataGetBytePtr获取实际字节（以及CGImageGet*了解如何解释它们的各种方法）。
无法相信这里没有一个正确的答案。无需分配指针，未相乘的值仍需归一化。切入正题，这里是 Swift 4 的正确版本。UIImage只需使用.cgImage.
extension CGImage {
func colors(at: [CGPoint]) -> [UIColor]? {
let colorSpace = CGColorSpaceCreateDeviceRGB()
let bytesPerPixel = 4
let bytesPerRow = bytesPerPixel * width
let bitsPerComponent = 8
let bitmapInfo: UInt32 = CGImageAlphaInfo.premultipliedLast.rawValue | CGBitmapInfo.byteOrder32Big.rawValue
guard let context = CGContext(data: nil, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo),
let ptr = context.data?.assumingMemoryBound(to: UInt8.self) else {
return nil
}
context.draw(self, in: CGRect(x: 0, y: 0, width: width, height: height))
return at.map { p in
let i = bytesPerRow * Int(p.y) + bytesPerPixel * Int(p.x)
let a = CGFloat(ptr[i + 3]) / 255.0
let r = (CGFloat(ptr[i]) / a) / 255.0
let g = (CGFloat(ptr[i + 1]) / a) / 255.0
let b = (CGFloat(ptr[i + 2]) / a) / 255.0
return UIColor(red: r, green: g, blue: b, alpha: a)
}
}
}
您必须首先将图像绘制/转换为缓冲区的原因是因为图像可以有几种不同的格式。需要此步骤才能将其转换为您可以阅读的一致格式。
NSString * path = [[NSBundle mainBundle] pathForResource:@"filename" ofType:@"jpg"];
UIImage * img = [[UIImage alloc]initWithContentsOfFile:path];
CGImageRef image = [img CGImage];
CFDataRef data = CGDataProviderCopyData(CGImageGetDataProvider(image));
const unsigned char * buffer = CFDataGetBytePtr(data);
这是一个 SO线程，其中@Matt 通过置换图像仅将所需像素渲染到 1x1 上下文中，以便所需像素与上下文中的一个像素对齐。
根据UIImage 上的 Apple Reference，该对象是不可变的，您无法访问支持字节。UIImage如果您使用 a （显式或隐式）填充 a 确实可以访问 CGImage 数据，但如果由 a 支持CGImage，它将返回，反之亦然。NULLUIImageCIImage
图像对象不提供对其底层图像数据的直接访问。但是，您可以检索其他格式的图像数据以在您的应用程序中使用。具体来说，您可以使用 cgImage 和 ciImage 属性来检索分别与 Core Graphics 和 Core Image 兼容的图像版本。您还可以使用 UIImagePNGRepresentation( :) 和 UIImageJPEGRepresentation( :_:) 函数生成一个 NSData 对象，其中包含 PNG 或 JPEG 格式的图像数据。
如前所述，您的选择是
如果您想要的输出不是 ARGB、PNG 或 JPEG 数据并且数据尚未由 CIImage 支持，那么这些都不是特别好的技巧。
在开发项目时，完全避免 UIImage 并选择其他东西可能更有意义。UIImage，作为 Obj-C 图像包装器，通常由 CGImage 支持，以至于我们认为它是理所当然的。CIImage 往往是一种更好的包装格式，因为您可以使用CIContext来获取您想要的格式，而无需知道它是如何创建的。在您的情况下，获取位图将是调用的问题
- 渲染：toBitmap:rowBytes:bounds:format:colorSpace:
作为一个额外的好处，您可以通过将过滤器链接到图像上来开始对图像进行很好的操作。这解决了很多图像颠倒或需要旋转/缩放等问题。
基于 Olie 和 Algal 的答案，这里是 Swift 3 的更新答案
public func getRGBAs(fromImage image: UIImage, x: Int, y: Int, count: Int) -> [UIColor] {
var result = [UIColor]()
// First get the image into your data buffer
guard let cgImage = image.cgImage else {
print("CGContext creation failed")
return []
}
let width = cgImage.width
let height = cgImage.height
let colorSpace = CGColorSpaceCreateDeviceRGB()
let rawdata = calloc(height*width*4, MemoryLayout<CUnsignedChar>.size)
let bytesPerPixel = 4
let bytesPerRow = bytesPerPixel * width
let bitsPerComponent = 8
let bitmapInfo: UInt32 = CGImageAlphaInfo.premultipliedLast.rawValue | CGBitmapInfo.byteOrder32Big.rawValue
guard let context = CGContext(data: rawdata, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo) else {
print("CGContext creation failed")
return result
}
context.draw(cgImage, in: CGRect(x: 0, y: 0, width: width, height: height))
// Now your rawData contains the image data in the RGBA8888 pixel format.
var byteIndex = bytesPerRow * y + bytesPerPixel * x
for _ in 0..<count {
let alpha = CGFloat(rawdata!.load(fromByteOffset: byteIndex + 3, as: UInt8.self)) / 255.0
let red = CGFloat(rawdata!.load(fromByteOffset: byteIndex, as: UInt8.self)) / alpha
let green = CGFloat(rawdata!.load(fromByteOffset: byteIndex + 1, as: UInt8.self)) / alpha
let blue = CGFloat(rawdata!.load(fromByteOffset: byteIndex + 2, as: UInt8.self)) / alpha
byteIndex += bytesPerPixel
let aColor = UIColor(red: red, green: green, blue: blue, alpha: alpha)
result.append(aColor)
}
free(rawdata)
return result
}
斯威夫特 5 版本
此处给出的答案要么已过时，要么不正确，因为它们没有考虑以下内容：
image.size.width/返回的点大小不同image.size.height。UIView.drawHierarchy(in:afterScreenUpdates:)方法可以生成 BGRA 图像。CGImage，像素行的大小（以字节为单位）可能大于像素宽度乘以 4 的大小。下面的代码是提供一个通用的 Swift 5 解决方案来获取UIColor所有此类特殊情况的像素。代码针对可用性和清晰度进行了优化，而不是针对性能进行了优化。
public extension UIImage {
var pixelWidth: Int {
return cgImage?.width ?? 0
}
var pixelHeight: Int {
return cgImage?.height ?? 0
}
func pixelColor(x: Int, y: Int) -> UIColor {
assert(
0..<pixelWidth ~= x && 0..<pixelHeight ~= y,
"Pixel coordinates are out of bounds")
guard
let cgImage = cgImage,
let data = cgImage.dataProvider?.data,
let dataPtr = CFDataGetBytePtr(data),
let colorSpaceModel = cgImage.colorSpace?.model,
let componentLayout = cgImage.bitmapInfo.componentLayout
else {
assertionFailure("Could not get a pixel of an image")
return .clear
}
assert(
colorSpaceModel == .rgb,
"The only supported color space model is RGB")
assert(
cgImage.bitsPerPixel == 32 || cgImage.bitsPerPixel == 24,
"A pixel is expected to be either 4 or 3 bytes in size")
let bytesPerRow = cgImage.bytesPerRow
let bytesPerPixel = cgImage.bitsPerPixel/8
let pixelOffset = y*bytesPerRow + x*bytesPerPixel
if componentLayout.count == 4 {
let components = (
dataPtr[pixelOffset + 0],
dataPtr[pixelOffset + 1],
dataPtr[pixelOffset + 2],
dataPtr[pixelOffset + 3]
)
var alpha: UInt8 = 0
var red: UInt8 = 0
var green: UInt8 = 0
var blue: UInt8 = 0
switch componentLayout {
case .bgra:
alpha = components.3
red = components.2
green = components.1
blue = components.0
case .abgr:
alpha = components.0
red = components.3
green = components.2
blue = components.1
case .argb:
alpha = components.0
red = components.1
green = components.2
blue = components.3
case .rgba:
alpha = components.3
red = components.0
green = components.1
blue = components.2
default:
return .clear
}
// If chroma components are premultiplied by alpha and the alpha is `0`,
// keep the chroma components to their current values.
if cgImage.bitmapInfo.chromaIsPremultipliedByAlpha && alpha != 0 {
let invUnitAlpha = 255/CGFloat(alpha)
red = UInt8((CGFloat(red)*invUnitAlpha).rounded())
green = UInt8((CGFloat(green)*invUnitAlpha).rounded())
blue = UInt8((CGFloat(blue)*invUnitAlpha).rounded())
}
return .init(red: red, green: green, blue: blue, alpha: alpha)
} else if componentLayout.count == 3 {
let components = (
dataPtr[pixelOffset + 0],
dataPtr[pixelOffset + 1],
dataPtr[pixelOffset + 2]
)
var red: UInt8 = 0
var green: UInt8 = 0
var blue: UInt8 = 0
switch componentLayout {
case .bgr:
red = components.2
green = components.1
blue = components.0
case .rgb:
red = components.0
green = components.1
blue = components.2
default:
return .clear
}
return .init(red: red, green: green, blue: blue, alpha: UInt8(255))
} else {
assertionFailure("Unsupported number of pixel components")
return .clear
}
}
}
public extension UIColor {
convenience init(red: UInt8, green: UInt8, blue: UInt8, alpha: UInt8) {
self.init(
red: CGFloat(red)/255,
green: CGFloat(green)/255,
blue: CGFloat(blue)/255,
alpha: CGFloat(alpha)/255)
}
}
public extension CGBitmapInfo {
enum ComponentLayout {
case bgra
case abgr
case argb
case rgba
case bgr
case rgb
var count: Int {
switch self {
case .bgr, .rgb: return 3
default: return 4
}
}
}
var componentLayout: ComponentLayout? {
guard let alphaInfo = CGImageAlphaInfo(rawValue: rawValue & Self.alphaInfoMask.rawValue) else { return nil }
let isLittleEndian = contains(.byteOrder32Little)
if alphaInfo == .none {
return isLittleEndian ? .bgr : .rgb
}
let alphaIsFirst = alphaInfo == .premultipliedFirst || alphaInfo == .first || alphaInfo == .noneSkipFirst
if isLittleEndian {
return alphaIsFirst ? .bgra : .abgr
} else {
return alphaIsFirst ? .argb : .rgba
}
}
var chromaIsPremultipliedByAlpha: Bool {
let alphaInfo = CGImageAlphaInfo(rawValue: rawValue & Self.alphaInfoMask.rawValue)
return alphaInfo == .premultipliedFirst || alphaInfo == .premultipliedLast
}
}
要在 Swift 5 中访问 UIImage 的原始 RGB 值，请使用底层 CGImage 及其 dataProvider：
import UIKit
let image = UIImage(named: "example.png")!
guard let cgImage = image.cgImage,
let data = cgImage.dataProvider?.data,
let bytes = CFDataGetBytePtr(data) else {
fatalError("Couldn't access image data")
}
assert(cgImage.colorSpace?.model == .rgb)
let bytesPerPixel = cgImage.bitsPerPixel / cgImage.bitsPerComponent
for y in 0 ..< cgImage.height {
for x in 0 ..< cgImage.width {
let offset = (y * cgImage.bytesPerRow) + (x * bytesPerPixel)
let components = (r: bytes[offset], g: bytes[offset + 1], b: bytes[offset + 2])
print("[x:\(x), y:\(y)] \(components)")
}
print("---")
}
https://www.ralfebert.de/ios/examples/image-processing/uiimage-raw-pixels/
基于不同的答案，但主要基于this，这可以满足我的需要：
UIImage *image1 = ...; // The image from where you want a pixel data
int pixelX = ...; // The X coordinate of the pixel you want to retrieve
int pixelY = ...; // The Y coordinate of the pixel you want to retrieve
uint32_t pixel1; // Where the pixel data is to be stored
CGContextRef context1 = CGBitmapContextCreate(&pixel1, 1, 1, 8, 4, CGColorSpaceCreateDeviceRGB(), kCGImageAlphaNoneSkipFirst);
CGContextDrawImage(context1, CGRectMake(-pixelX, -pixelY, CGImageGetWidth(image1.CGImage), CGImageGetHeight(image1.CGImage)), image1.CGImage);
CGContextRelease(context1);
由于这些行，您将拥有一个 AARRGGBB 格式的像素，其 alpha 在 4 字节无符号整数中始终设置为 FF pixel1。