Missing pixel information when rendering with matte object

[AC5L4T3R]

Hi guys,

Currently we're putting a configurator demo together and I have to render the wheels separately from the main body of the car. When I put the layers together in photoshop there seems to be some sort of padding going on, thus creating a small area between the fender and the tyre where there's no information.

See attached image.

Anyone got any ideas? Using 3.6.05

[vlado]

You need to tell PhotoShop that the images are with premultiplied alpha when loading them. Also make sure you render against black background.

Best regards,
Vlado

[dans]

Edit: If it is not simply what Vlado suggested and that line with "no information" in your screenshot is transparent then read on:

I'm not sure form your question if this is also a problem in your configurator or just something that you worried about when looking at your renders in Photoshop. I used to get similar questions from psd-manager users that generate masks/cutouts for all objects as Photoshop layers and then wonder why these thin lines appear between the layers on a transparent background if they make all layers visible.

Photoshop Experiment:
Put 2 solid layers above each other that are 50% transparent. What is the result? Dry the same with 70% and 30% opacity.
The same thing happens along these antialiased edge pixels. So this "gap" is normal with antialiased images.

Some ideas/workarounds:
A: Use a black base layer then add your configurable parts/layers on top using "Linear Dodge" (aka Add) blending mode (all parts need to be rendered on black, no layer transparency). If you want a background image then use the alpha channel of your render to create a "black hole" in it that fits your car and use "Linear Dodge" for this layer too
B If possible simply put a background behind everything that matches and covers these lines.

Daniel