lazy flares

21Mar08

I’m totally sick about huge overuse of CG lens flares, especially ae knoll chroma hoop and photoshop’s 35 mm.

So to fight with this i thought out cool method to kill a week – shooting to photo camera real lens flares, then combine them to HDRs and track them with light sources in ae.

Take cam with ability to shoot manually (Canon EOS 350D for example), LED light and a dark room without any kids and pets.

After thousands of boring tryouts come up wıth ruqirement of five different exposures for every frame (to compile HDRs) and about 100 LED light positions for enough smoothness of the flare’s movement.

Kiss your wife goodbye for a couple of days and locked myself into the dark room, and shoot there 500 frames, shining out to your eyes with 200 lm tactical LED light (i forgot to warn you – eyes and photo cam matrix will go to trash after all)

To automate shooting process for such a lot of frames use DSLR Remote Pro, it is helpful to remote control photo cam by usb. Set up the time lapse for 100 frames by every 30 seconds and exposure bracketing for 5 frames by 2 steps (by shutter speed)

Go out to daylight and after LED trails are dissapeared from the eyes let’s deal with HDRs.

Install Photomatix Pro for HDRs compiling, this software has an ability to automatically recognize EXIF info from shooted JPEGs. So feed to Photomatix all the JPEGs and go to bed. by mornig you will have 100 HDRs

Now it’s time for ae.

We have to figure out some kind of a system for motion of hdr on the screen. Lens flare basic feature is aperture ghosting, that moves opposite to light source by the center of the frame. So use the tracking method which covers this kind of movement.

To implement this scheme you’ll have to recall some basic trigonometry knowledge from school, particularly arc tangents and sum of the squares of the legs.

Do not forget to switch to 32-bit mode in ae for proper work with HDRs

Make comp 100 frames lenght, lad HDRs sequence and named it “photo-sequence”.

Make another comp with two previous comps layered and add null named “target”. Dimensions of this new comp should be one and half times less than comp with “photo-sequence”.

Enable time remapping for “photo-sequence” layer and use folowing expression:

x = thisComp.width/2 – thisComp.layer(“target”).transform.position[0]
y = thisComp.height/2 – thisComp.layer(“target”).transform.position[1]
Math.sqrt(x*x + y*y) * ((comp(“photo-sequence”).duration / comp(“photo-sequence”).frameDuration) / (comp(“photo-sequence”).width / 2)) * thisComp.frameDuration

For rotation of the same layer use this one:

x = thisComp.width / 2 – thisComp.layer(“target”).transform.position[0]
y = thisComp.height / 2 – thisComp.layer(“target”).transform.position[1]
z = 0
if (x > 0) {z = 180}
radiansToDegrees(Math.atan(y / x)) + z

Now if we move “target” – HDRs flares follow it. Notice, that we have a lack with the rays when “target” moving around the center of composition.

If you need to use true 32-bit motion blur it will be heplful to apply “Echo” effect for HDRs comp.

Finally track some CG light sources, applied tracking data to “target” position and link flares exposure to CG lights brightness.

All we need as a final step is to track any CG lamp, insert keys to position of “target” null and adjust exposure of the flares.

After days of shooting and boring hdr’s combining you could obtain a library of ajustable real lens flares

Anyway, great respect for Knoll Light Factory team!

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