在CIFilter中使用来自CIColor的CIImage：获取空图像 [英] Using a CIImage from CIColor in a CIFilter: getting empty image

问题描述

我正在尝试使用混合模式创建CIFilter（如叠加或乘法）。相关代码：

I'm trying to create a CIFilter with blend mode (like overlay or multiply). Relevant code:

// Let's try a filter here
// Get the data
NSData *imageData = UIImageJPEGRepresentation(image, 0.85);
// Create a CI Image
CIImage *beginImage = [CIImage imageWithData:imageData];
CIImage *overlay = [CIImage imageWithColor:[CIColor colorWithRed:0.7 green:0.75 blue:0.9 alpha:0.75]];
// Create a context
CIContext *context = [CIContext contextWithOptions:nil];
// Create filter
CIFilter *filter = [CIFilter filterWithName:@"CIOverlayBlendMode" 
                                  keysAndValues:@"inputImage", beginImage,
                                                @"inputBackgroundImage", overlay,
                                                nil];

其他过滤器工作正常（如棕褐色调），但过滤器需要inputBackgroundImage键，我得到一个空白/空结果......所以我的背景图像似乎有些问题。

Other filters are working okay (like sepia tone), but with a filter that requires a "inputBackgroundImage" key, I get a blank/empty result ... so something seems to be wrong with my background image.

如何通过在图像上放置纯色来使用混合模式滤镜？

How do I use a blend mode filter by placing a solid color over an image?

推荐答案

在主题入门代码中没问题，只需要一个修复。

Its okay in topic starter's code, only one fix should be.

NSData *imageData = UIImageJPEGRepresentation(image, 0.85);
// Create a CI Image
CIImage *beginImage = [CIImage imageWithData:imageData];
CIImage *overlay = [CIImage imageWithColor:[CIColor colorWithRed:0.7 green:0.75 blue:0.9 alpha:0.75]];

//You should crop the generated image to beginImage size because generated image's size is infinite. I don't know why, but CIOverlayBlendMode isn't tolerant to infinite size
    overlay = [overlay imageByCroppingToRect:CGRectMake(beginImage.extent.origin.x, beginImage.extent.origin.y, beginImage.extent.size.width, beginImage.extent.size.height)];

// Create a context
CIContext *context = [CIContext contextWithOptions:nil];
// Create filter
CIFilter *filter = [CIFilter filterWithName:@"CIOverlayBlendMode" 
                                      keysAndValues:@"inputImage", beginImage,
                                                    @"inputBackgroundImage", overlay,
                                                    nil];

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