Is This the World's Best HDTV Projector?

The picture quality that a Faroudja DILA projector produces begins and ends with a fanaticism for creating and perfecting the ultimate image. This passion for excellence, combined with sophisticated testing equipment and software, results in a projector that sets new levels of accuracy and quality - critical factors for recreating the film experience.

Until now, to obtain full HD resolution and color reproduction for home theater viewing required the use of a 9-inch CRT projector. Faroudja’s new DILA1080pHD projector finally offers an image that can match this performance in many ways, providing all the image quality benefits of the analog display with all the advanced features of the digital platform.

Faroudja has partnered with William Phelps for the calibration of our DILA projectors. William, an avid film enthusiast, is well known in the video industry for his expertise. His background includes 30 years as a programmer and software developer for IBM. Additionally, he is the Vice President of the Peninsula Astronomical Society with extensive knowledge of high performance optics and projection devices.

The Tools

The Projector
Many technical elements have come together for this new projector package that, for the first time, enables us to deliver a very high quality image from a digital display. The cornerstone of the system is the new DILA projector. The projector’s internal firmware allows for very precise adjustments in signal levels, making it possible to calibrate to the proper D65 colorimetry, accurate to three decimal places (+/- 0.002 x, y CIE). There are 128 level steps in the calibration process that the projector then interpolates to a total of 4096 steps of accuracy. The projector has exact adjustments for flat field performance across the entire image. High quality lenses deliver an image that stays sharp and in focus from corner to corner.

The high resolution 1920x1080 optical block finally allows for viewing full resolution High Definition content without the need for down-scaling. The photos below depict the ability to make every line visible in the image from the DILA1080p and show that these same lines are blurred in the image from the 9-inch CRT. (See photos).

The three chip design eliminates any rainbow effects seen with single pixel designs that require a color wheel. The tight pixel spacing prevents the pixel “screen door” effect. The screen door effect and rainbow artifact are problems that can occur with DLP-based displays.

The Test Equipment
The main calibration tool used is a three sensor Colorimeter with proprietary operational software. Colorimeters use a small number of filtered sensors which, on their own, are not as accurate as devices such as spectroradiometers but offer a faster response time and are less expensive. Before the Colorimeter is used, a reference is established for each projector using a GretagMacbeth™ LightSpex spectroradiometer. This device uses a diffraction grating to separate the visible spectrum into 256 elements. A highly accurate set of readings is taken for each of the primary colors (R, G, B), and white. The LightSpex is certified accurate to 4 decimal places, traceable to NIST (National Institute of Standards and Technology). The next step is to measure the same test patterns with the colorimeter and determine the delta between the two readings. William Phelps has written a custom program that then calibrates the colorimeter to match the results of the spectroradiometer to three decimal places. This allows him to use the colorimeter for faster calibration of the projectors but with the accuracy of the spectroradiometer.

As a final test, after all calibrations are done, the white point is rechecked with the spectroradiometer.

The Process
The first step in the calibration process is to determine the operating characteristics of the projector, such as what are the brightest and darkest points in the luminance curve where the unit can deliver a D65 gray.

Using a properly calibrated signal generator, the projector gray scale is initially calibrated to D65 using 16 luminance levels. Once the adjustments have been made, the process is repeated using 32 levels. The final run uses 128 levels!

The Look-up Tables (LUT) (the set of instructions in the unit that determine how much red, green and blue should be delivered by each pixel) in the DILA1080p and DILA788 are very high resolution so they allow for this level of accuracy.

D65 Errors
Many projector manufacturers will report their products deliver a flat 6500K color temperature. However, when viewed, the image appears cyan or pink. This is a result of errors in how color temperature is measured.

Color calibration software reports the reading taken by two methods, giving the XY coordinates and by stating the correlated color temperature (CCT) as degrees Kelvin. (The XY coordinates correspond to the CIE color chart).

The CCT is an estimate by the measurement instrument of what color temperature the X,Y readings would equate to on the Black Body curve. In the sample chart, the X,Y position is marked by the @. The CCT reading would state the closest point on the Black Body curve to @. It is possible that the CCT could report 6500K color temperature when the actual X,Y position is not at D65 (X=0.313, Y=0.329) due to the way CCT is calculated.

D65 is a precise point and is reproducible, CCT is not - if we adjust the projector so that it displays white as D65 (0.313, 0.329 in X,Y CIE 1931), then it will display white as a perfect white, not cyan or pink. It is important to realize that all colors then track from this white point, so if it is inaccurate, so is everything else. When done correctly, as is the case with Faroudja’s projectors, the picture quality is crisp, natural and filmlike.

In the charts above, custom software has been created to track the D65 Error. In the chart on the left, taken before calibration, the gray line tracks the reported color temperature (CCT) from the calibration software. The cyan line tracks the reading using the exact X,Y coordinates, which is the true gray scale reading. The difference between the two lines represents the D65 error. This projector manufacturer could report a color temperature of 6500K, when in fact the white point is way off.

The chart on the right tracks the CCT and the X, Y coordinates after the William Phelps optimizing. As you can see, both readings track exactly, with a D65 error over the entire chart at 0.003.

Proper Gamma
A key element of proper calibration is the gamma curve. The gamma curve defines how much light the projector should output for each luminance level for each pixel. The gamma is not a straight line. Its shape is partially determined by how the display recreates light. With William’s calibration, considerations are also applied for how the human eye sees light and the light characteristics of film.

This information is stored in a Look-up Table. Custom firmware has been created to fine tune the gamma curve to highly accurate levels (to three decimal points).

The DILA1080pHD projector is actually calibrated twice, with two gamma curves stored in its memory. One setting is optimized for Standard Definition sources such as DVD and satellite. The other setting is optimized for High Definition sources (ATSC). SD sources are typically stored as 8-bit; HD sources are typically 10-bit. The extra color depth the higher bit rate offers allows us to do some additional calibrating for information below the 20IRE level. This delivers greater shadow detail, getting us even closer to reproducing the characteristics of film.

The final step in the calibration process is critical. All the test equipment is turned off and we watch a movie! The image is judged using real images, not test patterns. The quality of the picture must please our most demanding customers. We know the accuracy of the image passes the test when the movie’s director, watching his own work in the home theater alongside of us, is thrilled with the results.

The Processor

All this calibration is meaningless if the signal sent to the projector is full of artifacts. The video processors packaged with the DILA projector are optimized to get the best performance possible. See our video processor white paper for details.

DILA788
The DILA788 projector is calibrated in the same way as the DILA1080p package outlined above. The two differences are:

1. The native resolution is 1400x788 (3-chip)
2. The second gamma curve memory for HD sources is not used.

Recreating the film experience is Faroudja’s ultimate goal. We believe that our new DILA projector packages, optimized and calibrated for perfection by renowned William Phelps, achieves this objective.

www.faroudja.com

By Pete Halenbeck