What you need to do is create an alpha channel with what you have. Fortunately, you are working over a black background, so this it’s pretty easy to do. There are tools within AE, but the quickest way will be to install the free plugin from knoll Unmult.
Once you have it installed, duplicate your layer and apply unmult to your layer. You will have an alpha channel now, but it will need to be adjusted. Change your color mode of the comp to from RGB to Alpha, and apply a levels effect to your layer. Change the levels channel to alpha and adjust the “alpha input white”. From your example I cranked it all the way down to 47. Now you can add an adjustment layer and apply CC Light Sweep. Animate the light sweep and use the alpha layer we created as a track matte to constrain the light sweep to just the text.
For the white to red effect, I duplicated the original layer again and added the effect Channels > Set Matte and for “Use For Matte” I chose the Red Channel. If you look at the individual channels the red has the greatest contrast. Then I used a levels affect again to affect the alpha channel(Alpha Input White = 157). Finally I used a Simple Choker with a negative value to expand the red a bit, play with this to taste. Finally I animated a red solid with an angled mask(to match the light sweep) and a large feather and used the layer as a track matte. Composite all together and it creates the effect you described, if I read what you were describing correctly.
Here’s my work project: 5215_alphachannelcreationfolder.zip
Johnny Cuevas, Editor
Thinkck.com
“I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work.”
—THOMAS EDISON on inventing the light bulb.