3 Replies Latest reply on Aug 28, 2009 8:51 AM by gravc

# LInear Dissolve shift in density

When dissolving over 14 frames from a white artwork to identical white artwork with a title, I am getting a dip in brightness and I do not understand why. Layer modes are NORMAL. Layer 1 fades from 100 percent to 0 percent, and layer 2 concurrently fades from 0 to 100 perent opacity.

At the 50/50 point, the brightness of the white card definitely dips. I am able to compensate somewhat  by pulling the bezier handles in the opacity to get a logarithmic curve, but why should that be necessary? 50 percent plus 50 percent  should equal 100 percent. There should be no change in brightness! What am I doing wrong??

thanks

Gravc

• ###### 1. Re: LInear Dissolve shift in density

Alpha Add blending mode! AE's default transparency blending is not linear. hence at 50%/50% the actual transparency is more like 80%, not 100%.

Mylenium

• ###### 2. Re: LInear Dissolve shift in density

As mylenium said, switch to alpha add blend mode.

So now you might wonder why 50+50 doesn't equal 100. It's because opacity, in real world, don't work this way. If you take a thin sheet of paper and tape it on your window, you'll see that light is coming through. This thin paper is about 50% opaque. Now if you tape a second sheet on top of it, you'll see that light is still comming thru. It's because the first sheet filters 50% of the incomming light, and the second sheet filters 50% of the 50% incomming light.

50% of 50% still leaves 25% light, and a third sheet would let 12.5% and so on and so on. And AE calculates it's opacity exactly like that. And as it's sometimes not conveniant (like in a cross dissolve) they added the alpha add, where 50%+50% = 100%.

• ###### 3. Re: LInear Dissolve shift in density

Thank you, Mylenium, that works great. I strongly suspected the answer lay in the layer modes.

regards

gravc