Black Level Tab

Requires Igloo Core Engine version 1.5.0+

Projectors tend to leak some light, even when displaying a completely black image. This light becomes very noticeable in the areas where projectors are overlapping.

To hide this noticeable light leak in the projector overlap areas, it helps to raise the light level in the areas where the projectors do not overlap.

When setting up the black level adjustment, then it is critical that the Warping and Blending has been correctly set, and the projectors have been turned on for at least 10mins.

This warm up period is critical, as the projectors mechanical and electrical parameters will change during this warm up period.

Some of the issues you might encounter are

Misaligned projector overlap areas – due to the mechanical properties of the projector optics.
Misaligned black level values, as the electrical properties of the lamp, DLP or SXRD chips changes.

Pre black level adjustment checklist

Make sure all the projectors are at normal operating temperature
Make sure all projectors are outputting the same luminance, using a bright image.
Make sure all Warp and Blend adjustments are done properly

Configuration

Setup the projector non overlap areas

Enable the ‘Black Level' tab: The Black level tab is hidden by default. To Enable, from the main menu bar ‘view > Black Level Tab’
Within the Black Level tab enable the Regioning Mode.
Enable the warping control points, they should now appear blue.
Using the normal Warping controls, mark the areas where the projectors do not overlap.

Setup the black level blending

Blending should only be used in cases where the projector has overscanning which cannot be disabled. Disabling projector overscan will provide much better results and will be significantly easier to maintain.

While the Black level regioning mode is enabled, then you can configure the blending using the normal blending tool’s. When using the Blending, a small overlap can be used to hide/smear out the sharp edge between the non-overlapped, and the overlapped area. This is achieved by defining the non-overlapped area a few pixels into the projector overlap area. If the blend area is too wide, then this can cause some unwanted artefacts within the blend area.

Configure the Black Level uplift parameter

Using the Uplift Amount, adjust the value to match the luminance of the center of the overlapped area.
Depending on the projector setup used in the installation, you maybe need to adjust the amount of uplift by different amounts to match the corners of the overlapped area. This can be done with the Upper left, Lower left, Upper right, Lower right and Right center compensation. Adjust these values to get the a uniform black level uplift.

Configure the Black Level roll off parameters

At higher luminance values, the adjustment at the non-overlapped regions can overshoot their luminance artificially as a result of the Black level adjustment at low luminance values. The parameters Threshold and Width correct the Black level adjustment for higher luminance values by gradually scaling its value to zero after a threshold luminance value.
The parameter Threshold controls the luminance value after which the Black level adjustment decays to zero. The parameter Width controls how fast the adjustment falls off to zero.
Figure 1 illustrates the shape of the Blacklevel rolloff as a function of image luminance. The x-axis represents the image luminance and the y-axis represents the scaling of the Black level adjustment. The Blacklevel Threshold value is 0.5 and the Blacklevel Width is 0.1.
Figure 2 shows the effect of changing the Blacklevel Threshold value to a lower value 0.2. The code snippet below can be used to visualise different Blacklevel rolloff shapes.

Export Black Level Settings

When done, enabled the Black Level checkbox in the Export Tab. Igloo Setup will then export a set of black level image masks and settings for Igloo Core Engine to use.