Fake Blood
Using Photoshop, and either After Effects or Premiere

Hello, this tutorial is more of a walkthrough of what I did for the blood effects in the Hallway Ambush test.

Since it is a walkthrough of sorts you're going to need to adapt this to whatever project you're working on, the techniques can certainly be applied to other videos.

Step 1
Film your footage

Pretty important really!
The filming for HA was a bit more complicated than neccessary for this tutorial, so I'm going to simplify. I'll be concentrating on the hallway section.

The camera cannot move. The below method depends on the camera never moving, if it does our blood is going to skip around all over the place. The camera movement in my video was created completely within After Effects. There is a video by Håkan "Zap" Andersson here that explains the theory behind that, if you're interested take a look.

I filmed an attacker twice with the intent of cloning him later (if you want more information on cloning, I recommend the cloning tutorial by Ken Lawton and the animated masks tutorial by David Nutley).

So now I have two videos (you only need one):

Step 2
Bring your footage into After Effects/Premiere

I'm going to be taking screenshots from AE, but pretty much everything is similar in Premiere too.

Alright, so you create a composition with the same size/framerate/length etc as your video and drag your video into it. Because I wanted to complicate things with cloning, I combined my two shots together to get this:

You should now have a composition with your video that you wish to add blood to sitting inside it. The next thing to do is to identify where during the video you want the blood to appear. For my shot, the clones don't react to a bullet hit until quite late on. Drag the work area selection until it encompases what you want to alter.

Step 3
Exporting for Photoshop

For Premiere go File>Export Movie>Settings and choose Filmstrip. For AE go Composition>Add to Render Queue. Check everything to best quality and your output format to be Filmstrip.

Render the file out to a folder of choice, save, and close After Effects/Premiere. Just to be safe, copy your new Filmstrip file and paste it somewhere else on your hard drive as a backup.

Step 4
Editing the Filmstrip

So now you need Photoshop to open up your newly created Filmstrip file. It should look like this:

but with many, many, many more frames. Save your Filmstrip file as a Photoshop file (PSD) and close your Filmstrip, we won't need that again for a while.
You need to have a rough idea of how the blood will look in the frame where it is most revealed. For my clip, this is the last few frames as both my clones fall to the floor revealing the walls behind them. For you it might be different (perhaps your character stands back up or something).

Having found this frame, create a new layer, and draw the blood over it, doesn't matter what colour. You might find this difficult to do without knowing where the blood has come from (for example, in my clip it is wiped down the side of a doorframe, very tricky to guess where the hand was from the last frame alone) so feel free to move your blood from frame to frame, improving its positioning as you do. Take time to get this right, it'll be worth it.

So after a while you should have something that looks like this:

Not too convincing yet, but we're getting there.

Step 5
Frame by Frame

This bit takes a while but is most important. Zoom right in on your bloodied frame and click the Rectangular Marquee Tool. Draw a selection close around the frame like this:

So now the one frame is selected. Still using your blood layer, scribble in the corners making sure to fill the furthest pixel in each corner.

The next step is to duplicate your blood layer, and to line it up with the nearerst frame using your corner scribbles as a guide to match it up perfect. You should now have two bloodied frames. Merge the two blood layers and copy this new layer, move it to two blank frames. Do this until every single frame that you want to have blood on it, has blood on it.

Fun huh? Nearly there. You should now have one blood layer, if you have more than one, merge them until you do. Now change the transfer mode for the blood layer to 'Color Burn'.

Looking a little more realistic now. You might want to experiment with different modes, maybe you prefer Multiply - whatever, play around with it.

So now you have an identical, realistic looking blood layer on most (if not all) frames. You now need to go through the sequence and erase the blood from every frame where it's not wanted. So if something obscures it like a hand, you need to erase the blood from where the hand covers.

In my video one of the clones slides down a wall, so I needed to erase the wipe before he falls.

While you go through frame by frame erasing the blood, you should also be erasing the scribbles you added in the corners - you don't need them any more. Instead add four new scribbles at the four corners of the complete strip.

Now that you have your blood added throughout the strip, you're ready to turn it back into video. Open up your Filmstrip and drag your blood layer from your Photoshop file onto your Filmstrip. Make sure you have Snap on (View>Snap) and drag the blood around until your corner markers are back in the corners (they should snap now). When done, erase them.

Flatten your image and click save. All done! Close Photoshop, open up your After Effects/Premiere project.

Step 6
Back into After Effects/Premiere

Import your modified Filmstrip file into AE/Premiere. Now add it to the composition that you rendered it from originally, making sure to place it as the top layer. It should be obvious where in your video it needs to be placed, with a bit of luck your timeline should still have the original selection on it.

That really is all there is to it! If you play through your video, you should have a nice stable blood effect appearing.

You'll notice I've replaced the original painting with an Indiana Jones IV poster. This was done using exactly the same method as the blood. because the camera never moves you can add all sorts of detail in Photoshop to enhance the scene. Perhaps a ruined city or a second moon.

It should be said that this technique can be replicated entirely within After Effects using masks, but I chose to use a Filmstrip file because I wanted the control offered by Photoshop. It really comes down to personal preference and the project it's needed for - you decide!

I hope this has been of some use for you, ideas, improvements or comments? - let me know!