我如何知道图像是否是“预乘 Alpha”？
我听说在进行图层混合等时只需要预乘 alpha。我如何知道我的原始图像是否是预乘 alpha？
I heard that only premultiplied alpha is needed when doing layer blending etc. How do I know if my original image is premultiplied alpha?
如果你对这篇内容有疑问，欢迎到本站社区发帖提问 参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。
绑定邮箱获取回复消息
由于您还没有绑定你的真实邮箱，如果其他用户或者作者回复了您的评论，将不能在第一时间通知您！
发布评论
评论（2）
你不能。
您唯一可以检查的是它是否没有预乘。为此，请检查所有像素并查看是否存在比 alpha 允许的值更高的颜色值
if(max(col.r,col.g,col.b) > 255* alpha)//不是预乘。任何其他情况都是不明确的，可以或不能预乘。您最好的猜测可能是假设它们并非如此，因为大多数 PNG 都是这种情况。编辑：实际上，即使我发布的代码也不起作用，因为有很多带有白色遮罩的 PNG，因此图像必须包含 alpha 为
0的部分来确定首先是哑光色。You can't.
The only thing that you can check is if it's not premultiplied. To do it go over all the pixels and see if there is a color-value that has a higher value than the alpha would permit
if(max(col.r,col.g,col.b) > 255*alpha)//not premul. Any other cases are ambiguous and could or could not be premultiplied. Your best guess is probably to assume that they aren't as that's the case for most PNGs.Edit: actually, not even the code that I posted would work as there are a lot of PNGs out there with white matte, so the image would have to include parts that have an alpha of
0to determine the matte color first.Android
Bitmap存储从带有预乘 Alpha 的 PNG 加载的图像。您无法以通常的方式从中获得非预乘的原始颜色。为了加载没有预乘 RGB 通道的图像，我必须使用此处的第 3 方
PNGDecoder：http://twl.l33tlabs.org/#downloadsAndroid
Bitmapstores images loaded from PNG with premultiplied alpha. You can't get non-premultiplied original colours from it in usual way.In order to load images without RGB channels being premultiplied I have to use 3rd party
PNGDecoderfrom here: http://twl.l33tlabs.org/#downloads