The Sony VPL-CS1 LCD projector uses three 0.7" polysilicon LCD panels that turn off and on, or modulate to some intermediate value for each color, Red, Blue and Green. In order to "make" black, each panel goes full on (blocking light), however the LCD panels are not entirely opaque and the light that "leaks" through each panel is added in the final image. This results in black really being a dark grey. The contrast level, which is the ratio of the light level produced when the panels are full off to when the panels are full on, contributes significantly to the "3D" look of the image.
To improve the contrast level I have tried three things:
1. Project the image on a "grey" vs. white screen surface, which absorbs more light and improves the perceived contrast level. This is a bit of a balancing act, as too much pigment in the screen will result in a grey or muddy white.
2. Color Correcting filter. I read an article on the internet about using color correcting filters with a Sony VW10HT projector, which uses a very similar lamp and LCD panels. The theory is that the lamp used has more light "power" available in the green and blue spectrum than the red, thus if you filter some of the blue and green out (with a red filter, I used a Red CC40) and crank the blue and green back up, you will have an overall better contrast ratio (darker blacks) without sacrificing overall image brightness. A key difficulty in implementing this with the VPL-CS1 is the inability to adjust the Red, Green and Blue levels at the projector (This may be accessible through a service menu, something I'm investigating. I suspect it will require service level software to do it. If you know how to do this, please share) Without this ability the adjustments must be made in the HTPC using the overlay color control. Preliminary results look promising but getting the overlay color controls to "stick" and getting them adjusted properly has proven daunting. I think I need to break down and build a light meter as described in the linked article to really get this right.
3. Adding a neutral density (grey) filter to the light path. I have tried two filters, one that reduced the light output by 4 f-stops, the other by 2. This seems to have a similar effect to the grey screen. In my opinion the overall light levels were reduced too severely to be acceptable. I figure the 2 stop filter reduced the illumination levels to less than 8 ft-lamberts, which seemed entirely too dim.
Conclusions:
Although not yet successful, I think that some upcoming software upgrades, including the TheaterTek software DVD player and updating the graphics card drivers will allow the color correcting filter solution to succeed.
UPDATE: The Color Correcting filter is now working. I upgraded the Radeon Video card drivers to version 7199, which support overlay controls. The color, contrast and apparent detail level are all considerably improved! I am moving this to success stories.
Also found out how to access the service menu and have subsequently tweaked the projectors settings to improve its gamma tracking. See the details of this here.
