将非透明像素转换为黑色

I'm looking for a way of converting an image so that all non-transparent pixels (those that have alpha != 1) into black and transparent pixels untouched (or converted to white). The closest I got was with the below imagemagick command:

我正在寻找一种方法来转换图像，使所有非透明像素(具有alpha != 1的像素)都变成不受影响的黑色和透明像素(或转换为白色)。我最接近的是下面的imagemagick命令:

convert <img> -colorspace Gray <out>

However this still gives me some gray colors instead of a complete black. I have tried all colorspace options and none does the job.

但是这仍然给了我一些灰色而不是完全的黑色。我尝试过所有的颜色空间选项，但是没有一个可以。

Any idea how I could achieve this with imagemagick or with similar tools (or with a PHP library if it exists)

我可以用imagemagick或者类似的工具(如果有PHP库的话)来实现这一点吗?

3 个解决方案

#1

I know this question is old, but now I've stumbled on it I might as well answer it.

我知道这个问题由来已久，但现在我偶然发现了它，我不妨回答它。

The ImageMagick command you want is:

您需要的ImageMagick命令是:

convert <img> -alpha extract -threshold 0 -negate -transparent white <out>

I'll breakdown what it's doing as well.

我也会分析它在做什么。

1. -alpha extract - Take the alpha mask of the image. Completely transparent pixels will be black, completely opaque ones white.
2. -alpha提取-获取图像的alpha蒙版。完全透明的像素是黑色的，完全不透明的像素是白色的。
3. -threshold 0 - Increase all channels to their maximum value if they are greater than zero. In this case, it will make every pixel white except the ones that are completely black.
4. -阈值0 -如果大于零，则增加所有通道的最大值。在这种情况下，它会使每个像素都变成白色，除了那些完全是黑色的像素。
5. -negate - Invert the image. Now our blacks are white and our whites are black.
6. -反相-反相图像。现在我们的黑人是白人，我们的白人是黑人。
7. -transparent white - Set white pixels to be transparent. This can be excluded if you'd prefer your originally transparent pixels to be white.
8. -透明白色-设置为透明的白色像素。如果您希望您最初的透明像素是白色的，那么可以排除这种情况。

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#2

I'm not sure whether it'll help you (i.e. whether the methods presented will leave the transparent pixels alone) but check out the answers to this question: PHP/ImageMagic Get the “shadow” of an image

我不确定它是否会对您有所帮助(例如，所提供的方法是否会保留透明像素)，但请检查这个问题的答案:PHP/ImageMagic获得图像的“阴影”

#3

Well, you could do it with GD and a pair of loops:

你可以用GD和一对环来做:

$img = imagecreatefromstring(file_get_contents($imgFile));
$width = imagesx($img);
$hieght = imagesy($img);

$black = imagecolorallocate($img, 0, 0, 0);
$white = imagecolorallocate($img, 255, 255, 255);

for ($x = 0; $x < $width; $x++) {
    for ($y = 0; $y < $width; $y++) {
        $color = imagecolorat($img, $x, $y);
        $color = imagecolorforindex($color);
        if ($color['alpha'] == 1) {
            imagesetpixel($img, $x, $y, $black);
        } else {
            imagesetpixel($img, $x, $y, $white);
        }
    }
}

Or, you could replace colors (this may or may not work):

或者，你可以更换颜色(这可能有用，也可能没用):

$img = imagecreatefromstring(file_get_contents($imgFile));
$maxcolors = imagecolorstotal($img);
for ($i = 1; $i <= $maxcolors; $i++) {
    $color = imagecolorforindex($i);
    if ($color['alpha'] == 1) {
        imagecolorset($img, $i, 0, 0, 0);
    } else {
        imagecolorset($img, $i, 255, 255, 255);
    }
}