BEst way to apply alpha mask to change BG without "ghosting!"

[nickdk]

I simply can't figure out how to properly use the alpha mask from my vray rendering via 3dsmax. I can't change the background without getting a ghosting effects on the edge of the new bg (I guess this is leftover pixels from the render)

But I thought the point with an alpha map was to tell photoshop exactly which pixels it should show and hide?

 

Help please!

[luthias42]

Did you check to make sure that the Alpha is at 100% white? Also you could use the Alpha to delete the BG in photoshop completely to make sure that nothing is ghosting.

[nickdk]

The alpha is indeed not completely white, I can see grades of white if I zoom in, do you know how to set it at completely white? And isn't it a catch 22, if it's completely white then it must be aliased and it would return a hard cut of the bg?

[luthias42]

the easiest way I know of is to place a blk vraylight material on everything and if your using a physical camera turn off exposure and set your BG color to 255 white in the environment slot that should give you a mask of the BG.

[Stephen Thomas]

You could try saving as a TGA and setting pre-multiplied alpha to off. This will make sure that the edge pixels of your render are not multiplied with whatever background colour you have during anti-aliasing. Also make sure you are loading the alpha properly as a selection by ctrl + left clicking on the channel, not just doing a select by colour range or using the magic wand tool before deleting.

[fourthand11]

In Photoshop you can adjust the mask of your adjustment layer. Say you have an Exposure adjustment layer that you are using to adjust only the background of your image. In the same box where the adjustment layer sliders are there is a TAB next to the adjustment tab where you can adjust the mask.

[fourthand11]

I put together a quick tutorial to show this process.

 

[ATTACH]43990[/ATTACH][ATTACH]43990[/ATTACH]