Fixing IR Contamination

[bouldersoundguy]

Of course it's always best to get it right in the camera, but sometimes things are beyond your control (or like me you didn't know until it was too late).

I shot some live music video for some friends who also had another person shooting some video. I thought it would be fun to put the two shots together for a more interesting final product. The camera I was using was an older Sony D8 tape camcorder while the other one was a newer little thing that recorded to flash memory. I realized that white balance could be a problem but went ahead anyway. After spending quite a bit of time tweaking the color correction (in Vegas 6) I got it close but was left with one particularly annoying feature. Some of the blacks in my footage had a weird tinge of color to them while the other camera's blacks were black. I had discovered infrared contamination.

I was determined to make it better, and I think I succeeded. Here are the steps I used:

1. Insert Chroma Key
2. Use dropper to grab good sample of weird tinge color, then adjust thresholds for optimum mask
3. Duplicate track and delete Chroma Key on second track
4. Insert HSL on second track and zero out the saturation
5. Insert Brightness and Contrast on second track and adjust for natural look in areas showing through the first track's mask

It's not perfect. It doesn't fix the altered contrast but it does greatly improve my footage by eliminating the weird tinge of color caused by my camcorder's infrared sensitivity.

Before and after:
IR_before_and_after.jpg

[TimStannard]

I'm at work on a cheap monitor so can't make out the IR issue at the moment, but I'm very impressed to see your friend's band has entered a timewarp and managed to get a twenty-something Jimmy Page on guitar!

[TimAndrews]

How does one recognise IR contamination?

[bouldersoundguy]

How does one recognise IR contamination?

Look for blacks that are unnaturally bright or have some odd color. On my old Sony CCD-TRV140 it shows up as a sort of magenta-ish color, but on other cameras the color is different. In my research on this I've read about blacks sometimes showing up as brown in some cameras. It first became obvious to me when I compared my footage to the video file of the same event from another camera. In the other video the blacks were all black and in mine some were black and some had the magenta-ish color depending on the fabric. The other camera had a good IR filter built in while mine did not, probably because it has Sony's Super NightShot feature and an IR filter would defeat it.

I have since purchased a color correction filter that I hope will give me the option of preventing IR contamination. It works well in my tests but I haven't done any real projects with it yet.

[vidmanners]

nOt sure about this, IR is very difficult to remove as it's a low frequency. Ultra violet is relatively easy and most zoom lenses have enough glass so it's not an issue (eg in landscape shots)...not to be confused with distant mist which our eyes can see.

Are you sure this isn't just a camera fault and you noticed it when you had footage from another newer camera?

Let's hope that new filter fixes it . . ideally by taking same-scenes with the other camera. What happens if you film an IR heater (eg like used in bathrooms...)?
You can also find a IR source at the Blacksmith - when forging metal, etc.

[bouldersoundguy]

nOt sure about this, IR is very difficult to remove as it's a low frequency. Ultra violet is relatively easy and most zoom lenses have enough glass so it's not an issue (eg in landscape shots)...not to be confused with distant mist which our eyes can see.

Are you sure this isn't just a camera fault and you noticed it when you had footage from another newer camera?

Once it hits the CCD and becomes an electrical signal it's no longer low frequency, it's extra brightness plus a visible color in the image.

With the right filter and the foreknowledge it's pretty easy to prevent. Many (most?) cameras have a built in to minimize IR contamination, but you can defeat those by stacking filters that reduce visible light. In my case I was using a Sony camera with Super NightShot. For that feature to work there can't be an IR filter, so it's not a fault as much as a design compromise.

Let's hope that new filter fixes it . . ideally by taking same-scenes with the other camera. What happens if you film an IR heater (eg like used in bathrooms...)?
You can also find a IR source at the Blacksmith - when forging metal, etc.

I've already tested the filter and it does prevent IR contamination, but I haven't determined what it does to other parts of the spectrum. The plot that came with the filter slopes down at the top of the visible spectrum.

IR sources (like heaters, fire etc.) aren't the issue. It's black objects with varying degrees of IR reflectivity under lighting with strong IR output (incandescent bulbs).