PHP imageconvolution()在左上角留下黑点

问题描述

我正在尝试使用以下代码来锐化调整大小的图像:

I'm trying to sharpen resized images using this code:

imageconvolution($imageResource, array(
        array( -1, -1, -1 ),
        array( -1, 16, -1 ),
        array( -1, -1, -1 ),
    ), 8, 0);

使用上面的代码对透明PNG图像进行锐化时，它会在左上角显示一个黑点(我尝试了不同的卷积核，但是结果是相同的).调整图像大小后，看起来还可以.

When the transparent PNG image is sharpened, using code above, it appears with a black dot in the upper left corner (I have tried different convolution kernels, but the result is the same). After resizing the image looked OK.

第一张图片是原始图片

第二张图像是锐化的

编辑:我怎么了?我正在使用从像素中提取的颜色.

EDIT: What am I going wrong? I'm using the color retrieved from pixel.

$color = imagecolorat($imageResource, 0, 0);
    imageconvolution($imageResource, array(
        array( -1, -1, -1 ),
        array( -1, 16, -1 ),
        array( -1, -1, -1 ),
    ), 8, 0);
            imagesetpixel($imageResource, 0, 0, $color);

imagecolorat是正确的功能吗?还是位置正确?

Is imagecolorat the right function? Or is the position correct?

EDIT2 :我已经更改了坐标，但是仍然没有运气.我已经检查了imagecolorat给出的透明度(根据此帖子).这是转储:

EDIT2: I have changed coordinates, but still no luck. I've check the transparency given by imagecolorat (according to this post). This is the dump:

array(4) {
   red => 0
   green => 0
   blue => 0
   alpha => 127
}

Alpha 127 = 100％透明.这些零可能会导致问题...

Alpha 127 = 100% transparent. Those zeroes might cause the problem...

推荐答案

看起来像卷积代码中的错误(在某些实现中，角落是特殊情况).

Looks like a bug in the convolution code (corners are special cases in some implementations).

作为一种解决方法，您可以使用imageSetPixel()将像素值保存在卷积之前的那个角上，然后再进行恢复.

As a workaround, you can save the pixel value in that corner just before the convolution and restore it afterwards, with imageSetPixel().

您需要保存的像素为(0,0)，可能还需要检查透明度(但我认为它应该仅与imageColorAt和imageSetPixel一起使用).

The pixel you need to save is at (0,0), and possibly you will need to also check the transparency (but I think it should work with just imageColorAt and imageSetPixel).

测试代码

我从上面发布的文件中忘了文件"giants.png".如果我不使用imageSetPixel，我会遇到与您相同的额外像素.使用imageSetPixel，图像对我来说看起来是正确的.

The file 'giants.png' I wgot from the one you posted above. If I do not use imageSetPixel I experience the same extra pixel you got. With imageSetPixel, the image looks correct to me.

我运行ImageSaveAlpha或设置Alpha混合的顺序可能略有不同.

Possibly there's some slight difference in the sequence I run ImageSaveAlpha or set alpha blending.

<?php
        $giants = ImageCreateFromPNG('giants.png');

        $imageResource = ImageCreateTrueColor(190, 190);

        ImageColorTransparent($imageResource, ImageColorAllocateAlpha($imageResource, 0, 0, 0, 127));
        ImageAlphaBlending($imageResource, False);
        ImageSaveAlpha($imageResource, True);

        ImageCopyResampled($imageResource, $giants, 0, 0, 0, 0, 190, 190, ImageSX($giants), ImageSY($giants));

        $color = ImageColorAt($imageResource, 0, 0);
        ImageConvolution($imageResource, array(
                        array( -1, -1, -1 ),
                        array( -1, 16, -1 ),
                        array( -1, -1, -1 ),
                ), 8, 0);
        ImageSetPixel($imageResource, 0, 0, $color);
        ImagePNG($imageResource, 'dwarves.png');
?>

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