Rendering png sequence issue

[Smeerik]

Hi!
I have this problem when I render this png sequence. Normaly it looks like this:

But when i render the png sequence with alpha premultiplied it looks like this:

It only happens somehow in the layer in wich I drew the face and I don't have any masks active.
I rendered a lot png sequences for this project and this is the first that came out looking like this.

[ematecki]

PNGs should never be premultiplied !

TVPaint still support premultiplied PNG for compatibility with some buggy software.
In TVPaint 11 you get now a warning when selecting premultiplied PNG.

[slowtiger]

My guess: those vanishing lines are on a layer set to Multiply, and in a spot where there's nothing else in the layers under it.

[Smeerik]

Ah the layer was set to Hard light must have clicked it by accident
May I asked why you should nog premultiply png's? i have used it for al my shots I rendered and I have no problems with it.

Thanks for the replies!

[ematecki]

May I asked why you should nog premultiply png's? i have used it for al my shots I rendered and I have no problems with it.

The PNG specs (available here : http://www.w3.org/TR/REC-png-multi.html" onclick="window.open(this.href);return false; , in "12.8. Non-premultiplied alpha") explicitly say PNGs are always NON-premultiplied...

12.8. Non-premultiplied alpha

PNG uses "unassociated" or "non-premultiplied" alpha so that images with separate transparency masks can be stored losslessly. Another common technique, "premultiplied alpha", stores pixel values premultiplied by the alpha fraction; in effect, the image is already composited against a black background. Any image data hidden by the transparency mask is irretrievably lost by that method, since multiplying by a zero alpha value always produces zero.
Some image rendering techniques generate images with premultiplied alpha (the alpha value actually represents how much of the pixel is covered by the image). This representation can be converted to PNG by dividing the sample values by alpha, except where alpha is zero. The result will look good if displayed by a viewer that handles alpha properly, but will not look very good if the viewer ignores the alpha channel.

Although each form of alpha storage has its advantages, we did not want to require all PNG viewers to handle both forms. We standardized on non-premultiplied alpha as being the lossless and more general case.