iOS:将 RGB 滤镜应用于灰度 PNG [英] iOS: Applying a RGB filter to a greyscale PNG

问题描述

我有一个灰度宝石顶视图.

I have a greyscale gem top view.

(PNG 格式，所以有 alpha 组件)

(PNG format, so has alpha component)

我想根据这张图片创建 12 个小尺寸按钮，每个按钮的颜色都不同.

I would like to create 12 small size buttons, each in a different colour, from this image.

为了整洁起见，我想在代码中而不是在某些艺术包中进行此操作.

For the sake of tidiness, I would like to do this within the code rather than externally in some art package.

谁能提供一个方法(甚至一些代码)来做到这一点?

Can anyone provide a method (or even some code) for doing this?

PS 我知道如何在 GL 中使用大量代码来完成它，我希望有一种使用核心图形/核心动画的更简单的方法

PS I am aware of how to do it in GL using a ridiculous amount of code, I'm hoping there is a simpler way using core graphics / core animation

工作解决方案，感谢以下答案的精彩

Working solution, thanks to awesomeness from below answer

    CGSize targetSize = (CGSize){100,100};
    UIImage* image;
    {
        CGRect rect = (CGRect){ .size = targetSize };

        UIGraphicsBeginImageContext( targetSize );
        {
            CGContextRef X = UIGraphicsGetCurrentContext();

            UIImage* uiGem = [UIImage imageNamed: @"GemTop_Dull.png"];

            // draw gem
            [uiGem drawInRect: rect];

            // overlay a red rectangle
            CGContextSetBlendMode( X, kCGBlendModeColor ) ;
            CGContextSetRGBFillColor ( X,  0.9, 0, 0,  1 );
            CGContextFillRect ( X, rect );

            // redraw gem 
            [uiGem drawInRect: rect
                    blendMode: kCGBlendModeDestinationIn
                        alpha: 1. ];

            image = UIGraphicsGetImageFromCurrentImageContext();
        }
        UIGraphicsEndImageContext();
    }

推荐答案

最简单的方法是将图像绘制成 RGB 颜色空间 CGBitmapContext，使用CGContextSetBlendMode设置kCGBlendModeColor，以及然后用纯色绘制它(例如用 CGContextFillRect).

The easiest way to do it is to draw the image into an RGB-colorspaced CGBitmapContext, use CGContextSetBlendMode to set kCGBlendModeColor, and then draw over it with a solid color (e.g. with CGContextFillRect).

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