使用p5.js实现RGB转CMYK时图像变黑、像素值被重置为0的问题求助

我正在做一个图像滤镜项目，其中两个滤镜需要转换色彩空间。其他功能类似的函数都运行得很正常，但这个RGB转CMYK的函数却出了问题——当alpha值为255时，整个图像会变成纯黑色，本质上就是根据alpha值把图像变成单一的深色。

补充说明：我使用的是p5.min.js库

经过调试和查看打印的像素颜色信息，我发现这个函数似乎被循环执行了两次：第一次运行时一切正常，但第二次会把所有RGB值都设为0。我绞尽脑汁也找不到问题所在，目前只明确了这个现象。

下面是我的代码：

//CMYK Colour space conversion
function rgbToCMYK(imgIn)
{
    var imgOut = createImage(imgIn.width, imgIn.height);
    
    imgOut.loadPixels();
    imgIn.loadPixels();
    
    //Loop through pixels
    for (var x=0; x<imgIn.width; x++){
        for (var y=0; y<imgIn.height; y++){
            var index = (x + (y * imgIn.width)) * 4;
            
            var r = imgIn.pixels[index +0];
            var g = imgIn.pixels[index +1];
            var b = imgIn.pixels[index +2];
            var a = imgIn.pixels[index +3];
            
            //Just checking that the program is reading the pixel info correctly
            console.log(r, "  ", g, "  ", b, "  ", a);
            
            //Convert rgb to CMY
            var computedC = 1 - (r/255);
            var computedM = 1 - (g/255);
            var computedY = 1 - (b/255);
            
            console.log(computedC, "  ", computedM, "  ", computedY);
            
            //Compute min CMY
            var minCMY = Math.min(computedC, Math.min(computedM, computedY));
            
            //Complete Conversion
            computedC = (computedC - minCMY) / (1 - minCMY);
            computedM = (computedM - minCMY) / (1 - minCMY);
            computedY = (computedY - minCMY) / (1 - minCMY);
            
            console.log(computedC, "  ", computedM, "  ", computedY);
            
            //K is not used yet
            var k = minCMY;
            
            imgOut.pixels[index + 0]] = computedC;
            imgOut.pixels[index + 1] = computedM;
            imgOut.pixels[index + 2] = computedY;
            imgOut.pixels[index + 3] = 125;
        }
    }
    imgOut.updatePixels();
    return imgOut;
}

我只调用了这个函数一次，它接收一张图像作为参数，本应完成色彩空间转换后返回处理后的图像。我对色彩空间转换完全是新手，甚至不确定自己的实现思路是否正确。

备注：内容来源于stack exchange，提问作者Luke Clark