image node: remove sampling error at missing_texture_color border

[aaronfross]

Hello,

The Missing Texture Color of an Arnold Image node is resulting in a spurious border at the edge of the texture. See the attached screen capture. The "decal" texture is a .PNG with no transparency. The border pixels are all white. The Missing Texture Color is set to pink. There's a black line at the border.

missing_texture_color_sample_error.png

This must be a sampling error. It looks like the edge pixels of the bitmap are being antialiased with their neighbors on all sides, including sides that don't have adjacent pixels. So basically the edge pixels are being blended with nothing, reducing their brightness.

I can make it a little better by changing the Filter Type of the Image node, but of course this changes the image sample quality. And it doesn't completely remove the spurious border.

In Maya, I can make the border disappear with the native File node's Coverage attributes. But it's not consistent, and when I change values back to their defaults, the spurious border does NOT reappear. This is most troubling.

If I want the Missing Texture Color to be the same as the bitmap, I can work around the issue by using Clamp mode and just inheriting the edge pixels. But if the Missing Texture Color needs to be different from the bitmap, we have a problem.

So, is there a workaround for this, or is this a bug / limitation in the way bitmaps are sampled? Could it be an artifact of mipmapping? I tried different Mipmap Bias settings to no avail.

Thanks,

Aaron

[thiago.ize · Accepted solution]

Thanks for catching this bug and reporting it!

We've now fixed this and assuming we don't detect any problems during our testing, the next release of arnold should contain this fix.

[aaronfross]

Awesome, that's great news. Thanks Thiago.