CIColorMap不会对输入图像均匀应用梯度

问题描述

我通过加载附加的蓝色到红色渐变图片创建了一个CIColorMap过滤器。

然后我试图将它应用于灰度输入图像，这只是一个线性渐变

当我在CIContext中绘制CIColorMap的图像时，目的是使黑色呈深蓝色，白色呈深红色，中间灰色呈白色。但实际结果如下：

正如你所看到的，中间的灰色实际上映射为淡蓝色，而不是我预期的白色。

下面是源代码。我不知道我是否使用CIColorMap错误地给出了非常稀缺的文档。

  //接口文件
 #import< ; Cocoa / Cocoa.h> 
 @interface ColorMapView：NSView 
 @end 
 
 //实现文件
 #import< QuartzCore / QuartzCore.h> 
 #importColorMapView.h
 
 static size_t imageWitdh = 512; 
 static size_t imageHeight = 125; 
 
 @implementation ColorMapView {
 CIImage * m_backgroundImage; 
 CIImage * m_colorMapGradient; 
 CIFilter * m_colorMapFilter; 
 CIContext * m_ciContext; 
} 
 
  - （instancetype）initWithCoder：（NSCoder *）coder {
 self = [super initWithCoder：coder] 
 if（self）{
 [self initBackgroundImage]; 
 [self initColorMapGradient]; 
} 
 return self; 
} 
 
  - （void）drawRect：（NSRect）dirtyRect {
 [super drawRect：dirtyRect]; 
 
 if（！m_ciContext）{
 m_ciContext = [CIContext contextWithCGContext：[NSGraphicsContext currentContext] .graphicsPort options：nil]; 
} 
 
 CGFloat x =（self.bounds.size.width  -  imageWitdh）/ 2; 
 CGFloat y =（self.bounds.size.height  -  imageHeight）/ 2; 
 
 //这里绘制代码。 
 [m_colorMapFilter setValue：m_backgroundImage forKey：kCIInputImageKey]; 
 [m_ciContext drawImage：[m_colorMapFilter valueForKey：kCIOutputImageKey] inRect：CGRectMake（x，y，imageWitdh，imageHeight）fromRect：m_backgroundImage.extent]; 
} 
 
  - （void）initBackgroundImage {
 CGColorSpaceRef colorSpace = CGColorSpaceCreateWithName（kCGColorSpaceGenericGray）; 
 CGContextRef context = CGBitmapContextCreate（NULL，imageWitdh，imageHeight，8，imageWitdh，colorSpace，（CGBitmapInfo）kCGImageAlphaNone）; 
 CGFloat locations [2] = {0.0，1.0}; 
 CGFloat components [4] = {0.0，1.0，1.0，1.0}; 
 CGGradientRef gradient = CGGradientCreateWithColorComponents（colorSpace，components，locations，2）; 
 CGContextDrawLinearGradient（context，gradient，CGPointMake（0，0），CGPointMake（imageWitdh，0），NO）; 
 CGImageRef gradientImage = CGBitmapContextCreateImage（context）; 
 CGContextRelease（context）; 
 CGGradientRelease（gradient）; 
 CGColorSpaceRelease（colorSpace）; 
 m_backgroundImage = [CIImage imageWithCGImage：gradientImage]; 
 CGImageRelease（gradientImage）; 
} 
 
  - （void）initColorMapGradient {
 NSString * imagePath = [[NSBundle mainBundle] pathForResource：@blue_red_scale_gradientofType：@png]; 
 CGDataProviderRef dataProvider = CGDataProviderCreateWithFilename（imagePath.UTF8String）; 
 CGImageRef image = CGImageCreateWithPNGDataProvider（dataProvider，NULL，NO，kCGRenderingIntentDefault）; 
 m_colorMapGradient = [CIImage imageWithCGImage：image]; 
 CGImageRelease（image）; 
 m_colorMapFilter = [CIFilter filterWithName：@CIColorMap]; 
 [m_colorMapFilter setValue：m_colorMapGradient forKey：@inputGradientImage]; 
} 
 
 @end 
  

解决方案>

这似乎是与颜色管理问题有关。如果我在创建CIContext对象时将kCIContextWorkingColorSpace设置为NSNull，我将得到预期的结果。

  if（！m_ciContext）{
 NSDictionary * options = @ {kCIContextWorkingColorSpace：[NSNull null]}; 
 m_ciContext = [CIContext contextWithCGContext：[NSGraphicsContext currentContext] .graphicsPort options：options]; 
} 
  

I created a CIColorMap filter by loading the attached blue-to-red gradient image.

Then I tried to apply this to a gray scale input image, which is simply a linear gradient from black to white.

When I draw the out image of CIColorMap in a CIContext, the intention is to render black color in dark blue, white color in dark red, and mid gray in white. However the actual result looks like:

As you can see, the mid gray is actually mapped to light blue, instead of white as I have expected.

Below is the source code. I wonder if I have been using CIColorMap incorrectly given the very scarce documentation.

// Interface file
#import <Cocoa/Cocoa.h>
@interface ColorMapView : NSView
@end

// Implementation file
#import <QuartzCore/QuartzCore.h>
#import "ColorMapView.h"

static size_t imageWitdh = 512;
static size_t imageHeight = 125;

@implementation ColorMapView {
    CIImage *m_backgroundImage;
    CIImage *m_colorMapGradient;
    CIFilter *m_colorMapFilter;
    CIContext *m_ciContext;
}

- (instancetype)initWithCoder:(NSCoder *)coder {
    self = [super initWithCoder:coder];
    if (self) {
        [self initBackgroundImage];
        [self initColorMapGradient];
    }
    return self;
}

- (void)drawRect:(NSRect)dirtyRect {
    [super drawRect:dirtyRect];

    if (!m_ciContext)  {
        m_ciContext = [CIContext contextWithCGContext:[NSGraphicsContext currentContext].graphicsPort options:nil];
    }

    CGFloat x = (self.bounds.size.width - imageWitdh) / 2;
    CGFloat y = (self.bounds.size.height - imageHeight) / 2;

    // Drawing code here.
    [m_colorMapFilter setValue:m_backgroundImage forKey:kCIInputImageKey];
    [m_ciContext drawImage:[m_colorMapFilter valueForKey:kCIOutputImageKey] inRect:CGRectMake(x, y, imageWitdh, imageHeight) fromRect:m_backgroundImage.extent];
}

- (void)initBackgroundImage {
     CGColorSpaceRef colorSpace = CGColorSpaceCreateWithName(kCGColorSpaceGenericGray);
    CGContextRef context = CGBitmapContextCreate(NULL, imageWitdh, imageHeight, 8, imageWitdh, colorSpace, (CGBitmapInfo)kCGImageAlphaNone);
    CGFloat locations[2] = {0.0, 1.0};
    CGFloat components[4] = {0.0, 1.0, 1.0, 1.0};
    CGGradientRef gradient = CGGradientCreateWithColorComponents(colorSpace, components, locations, 2);
    CGContextDrawLinearGradient(context, gradient, CGPointMake(0, 0), CGPointMake(imageWitdh, 0), NO);
    CGImageRef gradientImage = CGBitmapContextCreateImage(context);
    CGContextRelease(context);
    CGGradientRelease(gradient);
    CGColorSpaceRelease(colorSpace);
    m_backgroundImage = [CIImage imageWithCGImage:gradientImage];
    CGImageRelease(gradientImage);
}

- (void)initColorMapGradient {
    NSString* imagePath = [[NSBundle mainBundle] pathForResource:@"blue_red_scale_gradient" ofType:@"png"];
    CGDataProviderRef dataProvider = CGDataProviderCreateWithFilename(imagePath.UTF8String);
    CGImageRef image = CGImageCreateWithPNGDataProvider(dataProvider, NULL, NO, kCGRenderingIntentDefault);
    m_colorMapGradient = [CIImage imageWithCGImage:image];
    CGImageRelease(image);
    m_colorMapFilter = [CIFilter filterWithName:@"CIColorMap"];
    [m_colorMapFilter setValue:m_colorMapGradient forKey:@"inputGradientImage"];
}

@end

解决方案

It seems this is related to color management issue. If I set kCIContextWorkingColorSpace to NSNull when creating CIContext object, I will get expected result.

if (!m_ciContext)  {
    NSDictionary *options = @{kCIContextWorkingColorSpace : [NSNull null]};
    m_ciContext = [CIContext contextWithCGContext:[NSGraphicsContext currentContext].graphicsPort options:options];
}

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