在iOS中以编程方式创建渐变图像 [英] Create gradient image programmatically in iOS

问题描述

我正在尝试处理一些直接来自设备相机的图像数据。为了理解CGImage结构，我使用缓冲区来创建一个不适合我的图像（我知道我不应该在Obj-C代码中使用C代码，它只是为了理解）。代码如下：

I'm trying to process some imagedata which comes directly from the device camera. In order to understand the CGImage structure, I'm using a buffer to create an image which doesn't work right for me (I know that I shouldn't use C code within Obj-C Code, it's just for understanding). The code is as follows:

int *outBuf = malloc(sizeof(int) * width * height);
for (int i = 0; i < width * height;i ++)
{
     outBuf[i] = (((float)i) / ((float) width * height)) * 255.f;
}
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();

CGContextRef ctx = CGBitmapContextCreate(outBuf, width, height, 8, width * 4, colorSpace, kCGImageAlphaNone);

CGImageRef img = CGBitmapContextCreateImage(ctx);
CFRelease(ref);
CGContextRelease(ctx);
free(outBuf);

CGColorSpaceRelease(colorSpace);

[view.imgView setImage: [UIImage imageWithCGImage:img]];

CGImageRelease(img);

这应该创建从第一个像素到最后一个像素的渐变，但它会产生一个奇怪的graphic：

This should create a gradient from the very first to the very last pixel, but it results in a weird graphic:

水平间距来自哪里？ （我想解决这个问题，我知道还有其他可能来绘制渐变）在此先感谢。

Where do the horizontal spacings come from? (I want to solve this issue, I'm aware that there are other possibilities to draw the gradient) Thanks in advance.

推荐答案

我找到了解决方案：

我用int *初始化缓冲区。每个int长4个字节，但灰度图片每个像素只需要1个字节。将缓冲区更改为char *并修改CGBitmapContextCreate参数修复了问题：

I was initialising the buffer with int*. Every int is 4 bytes long, but a grayscale picture just needs 1 byte per pixel. Changing the buffer to char* and modifying the CGBitmapContextCreate parameters fixed the issue:

CGBitmapContextCreate(outBuf, width, height, 8, width, colorSpace, kCGImageAlphaNone);

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