Color Co-ordinated

ARTICLE

COLOR CO-ORDINATED
Colorimetry and Electronic Cinema

by Peter H. Putman, CTS

Electronic cinema is a hot topic for 1999, drawing lots of interest from major studios, theater owners, and large-screen display manufacturers. The emergence of high-definition television (HDTV) is adding more fuel to the fire, as are digital playback formats and satellite program distribution.

There are many issues to be resolved before e-cinema can take its place in the entertainment mainstream, such as security (how do you protect against unauthorized copying of bitstream-delivered featured films?), and image quality (what bit rate and compression scheme should be used for program delivery?).

Until recently, the biggest stumbling block to electronic cinema had been the projectors themselves. It wasn't technically feasible to project large, wide-screen images with brightness, contrast, and color saturation that even came close to 16mm film, let alone 35mm. But that has all changed in the past six years with the introduction of imaging engines based on transmitted light (liquid-crystal displays), reflected light (Digital Light Processing®), and hybrid light-shutter (Image Light Amplifier©) technology.

While none of these technologies are ready to replace film immediately, impressive demonstrations of film-like projection quality are being made on a daily basis. Texas Instruments has been busy showcasing standard 4:3, 16:9, and anamorphic 2.35:1 electronic cinema to several studios, using three 1280x1024-pixel digital micromirror devices (DMDs). Hughes-JVC recently announced a joint partnership with QUALCOMM in a new company called CineComm, formed "to replace a century-old tradition of celluloid with an end-to-end digital system" , based on the super-bright ILA-12K cinema-grade projector.

It's clear that there is some serious money behind finding and developing an alternative distribution for film-based entertainment. While features and shorts will continue to be shot on film for some time, some will ultimately be converted to digital data and remain in that form all the way to the newest megaplex. This digital data will also be re-purposed for delivery in the home rental market (DVD and other disc delivery systems) as well as eventual broadcast (DTV and HDTV).

THE VISION THING

As audiences, we crave film projection because it delivers pictures as close to reality as we're likely to get in an "artificial" perceptual environment. With high resolution, random grain, wide contrast, and a seemingly-infinite palette of colors, 35mm motion picture film has set a very high standard for electronic projection systems to hurdle - but they're getting closer with each passing year.

With the adoption of high-brightness short-arc xenon lamps and efficient optical paths, the brightness of many high-end electronic projectors is now on a par with conventional film projectors. Improvements in switching speeds, aperture ratios, polarization, and optical coatings have taken electronic projectors from washed-out, flat images just five years ago to rich, contrasty blacks and whites.

Fixed-resolution displays such as DMDs and LCDs have now reached over 1000 vertical pixels and are flirting with 1200, while resolution-independent imaging systems like the ILA and the liquid crystal light valve (LCLV) are capable of 1500 and more vertical lines. In terms of brightness, contrast, and resolution, e-cinema projection systems are looking like serious contenders.

But there's one last variable to contend with - color. Color is both qualitative and quantitative, and evokes all kinds of responses from different viewers. Artists debate it, printers go crazy trying to match it, art directors argue with post houses about it, companies spend thousands of dollars trying to measure it, and cinematographers and lighting directors devote their careers to manipulating it.

Color is a contentious issue for everyone from camera operators to transfer houses, and it's usually due to misunderstandings about how colors are created, the differences between additive and subtractive color, how color palettes (or "spaces") are defined, and how colors are reproduced and viewed. To get a handle on the color quality requirements for electronic cinema, we should take a closer look at the nature of color.

COLOR ABCs

There are two processes by which colors are created. The first, known as "additive" color, is simply the combination of red, green, and blue (RGB) primaries to achieve a full palette of color shadings. The addition of equal amounts of red, green, and blue results in white light, which we can verify by using a prism to refract these colors back out. Increasing the intensity of each primary color also increases brightness, or luminance.

The second color system - "subtractive" color - is the basis for pigments, dyes, and inks. In this system, the addition of all three cyan, magenta, and yellow (CMY) primaries results in black, and the absence of all three colors results in a white image. Increasing the density of each color decreases brightness in a subtractive system.

Incident light from sources like the sun and projection lamps is considered additive. However, when light strikes any surface, portions of its color spectra are absorbed or reflected. The reflected light gives us the color of that surface, while the absorbed wavelengths are subtracted. If the surface is an equal-energy reflector, the resulting surface color should have no color impurities. If not, we may see a reddish or bluish tint to the reflected image.

(The same holds true for incident light. The sun is an equal-energy light source, containing a fairly "flat" spectral response from red to blue. Artificial lights like metal-halide or tungsten-halogen studio lamps are not and are usually deficient in certain colors.)

I NEED MY SPACE

The total numbers of colors that exist in any system defines a color space, also known as a color gamut. There are several color spaces/gamuts; each resembling a rough triangle shape. The coordinates for each point of this triangle can be mathematically expressed as x,y coordinates, although the actual appearance of a color space is more like a 3D "anthill" - the third dimension (z-coordinate) being luminance.

The number of colors that can be defined within any color space is determined by the maximum shades of gray possible (luminance), along with the three primary colors used to mix and derive other colors. Because the sun is capable of generating an intense amount of both visible and invisible (infrared and ultraviolet) light, its natural color palette - or color space - is by far the widest. In fact, there are millions of natural colors we'll never see, as our eyes are incapable of responding to them.

What further complicates matters is the fact that our eyes don't see all colors with equal sensitivity. We are most sensitive to yellowish-green light (59%), followed by red (30%), and blue (11%). This human color response was first plotted in 1931 by the International Commission of Lighting (CIE in French), but also forms the basis of our present-day analog NTSC color television system and the CCIR-601 digital color specification. The 1931 CIE chart was the first to plot specific mathematical values, thereby defining a real, measurable color space.

Disappointed to learn there are colors you can't see? Guess what - there are colors you can see, but can't be reproduced on a television monitor! The phosphors used in TV sets (as well as studio monitors) have their own coordinates on the CIE diagram to ensure consistency from one monitor to another. So, we must further truncate our color boundaries in order to stay within a "phosphor-friendly" range. In North America, it's known as the SMPTE 'C' color space.

Now we can create any colors we wish for our broadcast electronic images, as long as they are derived from color values contained entirely within these boundaries. This may sound a bit restrictive, but without standardization there would be no way to assure a consistent color match from one monitor to another. Because the SMPTE 'C' space is much smaller than the visible color space, it's virtually impossible to display the saturated colors created by rainbows, prisms, or "pure" coherent light sources like lasers.

As television evolves into a digital form, there's a color space to go with it and the current boundaries are determined by the CCIR-601, YUV standards. This system has its roots in the CIE color diagram, with the difference being that colors are determined by digital sampling of luminance and two chrominance signals in a 4:2:2 ratio - not the relative levels of analog voltages. The color space for HDTV - a pure digital format - is also very close to the CCIR-601 and SMPTE 'C' coordinates.

It makes sense to use the CCIR-601 color palette for all aspects of electronic media production and display, regardless of whether the final product is shown on television, transferred to disk or tape, or viewed in a theater. The evidence so far is that film-to-601 data transfers - and even 601 data-to-film projects - compare favorably to "pure" film-based colorimetry, assuming the data-to-film transfers are done with tight controls on color consistency.

For example, selected screenings of "Saving Private Ryan" this past summer were accompanied by trailers for Reebok and Sony that originated on 35mm stock and were posted as D1 video for national TV spots. Tape House Digital Film in New York took this D1 material, eliminated the 3:2 pulldown and reduced the frame rate to 24 fps, then repositioned the material to 1.85:1 aspect.

After checking for any field "glitches", the data was then recorded to film at 2K resolution using proprietary pixel scaling software and conversion from CCIR-601 YUV to RGB color space. The result? Image quality was comparable to any other "Coming Attractions" intermixed with these film-to-digital video-to-data-to-film spots.

DROP THAT MOUSE!

By definition, the colors which exceed the 75% saturation limits of NTSC are known as "illegal" colors, although you won't get arrested for trying to use them. Print designers and art directors are often frustrated with the inability to reproduce specific CMYK print (subtractive) colors in the CCIR-601/SMPTE 'C' phosphor (additive) space, and often ask for color saturation levels to be boosted to get their special hue.

A creative colorist can "jigger" a monitor or play other tricks with color to get a "buy" from a client, but it's a sure bet those colors will never see the light of day when viewed on a conventional video monitor. The reason? "Jiggered" luminance levels will fall outside the SMPTE 'C' space. If you need more saturation in printed color, you add more ink. However, if you increase luminance (and thus saturation) of a video color, you'll run out of head room in the encoded, baseband NTSC video signal.

Some examples of "illegal" colors in the NTSC system that also fall outside the SMPTE 'C' color space include turquoise, lime green, indigo, cherry red, and pumpkin orange. (Not coincidentally, all of these shades are located near the very edges of the visible color space.) You may be able to reproduce one or more of these colors on a standard RGB monitor, where saturation levels are dialed in 255 steps and color matching systems like Pantone© are used. But you'd need to transfer the data back to film, or use a dichroic RGB projection system to view 'em.

The shift to digital media production is producing many skilled colorists who like to experiment within the precise coordinates of the CCIR-601 color space. By careful tightrope walking along the edge of the SMPTE 'C' curves, the resulting images have an almost "illegal" look with saturated reds and oranges, glowing pastel colors and even something that resembles the seemingly-unattainable turquoise shading.

IN THE THICK OF IT

To get a better perspective on color spaces and digital media production, I spent a few hours at the Advanced Imaging Center at Tape House in New York City, a busy film-to-digital transfer and HDTV edit/post facility. With its sister digital-to-film operation Tape House Digital Film, AIC creates many spots, trailers, and other projects for both broadcast and theatrical release. AIC installed the first Philips Spirit DATACINE in the world, and is active in data conversion from film to both HDTV and DTV.

AIC's vice-president and Spirit DATACINE director John Dowdell III is well-known for his transfers and coloring, producing work for Miramax and Merchant/Ivory Productions, as well as Ken Burns' Baseball, Lewis & Clark and Frank Lloyd Wright miniseries. His transfer suite revolves around Pandora's Pogle color correction system, and the bulk of his work is converting from 35mm negative to 1920x1080 files.

"When we work with digital data transfers, we standardize on the 601 color space", said Dowdell. "There's absolute consistency and predictability to staying within that color gamut that facilitates moving from film to data, doing composites, layering effects, and even transferring back to film." The Spirit is capable of 4:4:4 sampling, recording luminance information at 1920 pixels of resolution per line and full-depth RGB color.

I viewed a mix of both 35mm and HD footage from a D5 machine using a small Sony VPL-W400Q 16:9 dichroic LCD projector, and there were plenty of saturated colors to be seen. "The Spirit records a much wider gamut of colors than can be seen within the SMPTE 'C' color space", said Dowdell. "You'd need an RGB display to view them, but they're in the data. When files are transferred back to film, all of those colors are retained."

This means that a client may not be able to see a desired color, unless an LCD or DLP projector was available. "Pushing the limit on color saturation is a common request in TV spots, like cosmetics", Dowdell commented. "The Spirit has enough pixel sampling depth to bring out more subtle shades of a color, like those seen in lipstick ads. The Spirit's color matrix results in the correct luminance values for each color. We can achieve excellent color saturation and absolute color accuracy."

A few blocks away at Tape House Digital Film, David Kuttner, director of research and development, works with a wider color gamut than SMPTE 'C' - his area of concern is transferring data files back to film using Solitaire recorders, and he's currently looking at other high-performance film recording systems.

"We use dozens of color look-up tables for our Solitaire film recorders, and we're constantly modifying them to preserve all the colors seen in 601 data files" said Kuttner. "Our calcits monitor the intensity of each color plane. We're also constantly checking film gamma to match the SMPTE 'C' phosphors. It's a never-ending process that involves lots of little tweaks."

Kuttner agreed that achieving a "film look" will be the toughest challenge for any electronic cinema system. "Film has a greater color depth than video, and tracks color logarithmically, like the human eye. Any electronic projection system will need to support 36-bit color with 12 bits per color plane. 150:1 contrast will probably the minimum acceptable grayscale, although daylight film stocks can achieve 1,000:1 contrast."

The minimum resolution needed to approximate film projection? "Probably a 2K image to be acceptable - 2048x1556 pixels, said Kuttner. "That works out to an enormous file, typically 75 MB per frame. It also provides more color shadings at the low end of the grayscale, key to film-like quality." Considering none of the cinema-quality projectors currently offered for sale use 12-bit RGB processing, that would appear to be the next big hurdle in the evolution of e-cinema.

What about viewing colors in a transfer suite? Dowdell uses a BARCO 20" monitor with a MegaCalibrator system for precise color matching, and recently ordered a Digital Projection Power 3gv for projecting footage onto a 9' wide front screen. "The colorimetry of the Power 3gv is the best I've seen. I can get a good match to the 601 color space, plus the digital modulation system results in more accurate grayscale reproduction", he said. "And grayscales are what it's all about, if electronic projection is to approach film projection."

RUN THE GAMUT

It would appear that the determination of a "standard" color space for film-to-data transfers and eventual electronic projection is emerging by consensus - not edict. There is already a move afoot to push for a 1080p, 24 fps HDTV standard, which would be 100% compatible with film projection and eliminate any need for a 3:2 pull-down in data transfer. The evolution of this particular standard will also be by consensus.

And so it goes with color space. Staying within the CCIR-601 color gamut makes sense for another reason: Many cinema-grade electronic projection systems are adding direct serial digital inputs for both D1 and HDTV signal sources, ensuring that colors in the final projected image will match the colors seen in the film-to-data transfers, regardless of how many copies are made or when they are distributed.

With the eventual adoption of 10-bit and 12-bit pixel sampling, electronic projection systems will be able to show a far wider and richer palette of colors, helping them close the gap even more with 35mm film projection systems.

This article will appear in the February 1999 issue of Millimeter.

©1999 Peter H. Putman / Primedia Intertec


						ARTICLE
					COLOR CO-ORDINATED Colorimetry and Electronic Cinema


					by Peter H. Putman, CTS Electronic cinema is a hot topic for 1999, drawing lots of interest from major studios, theater owners, and large-screen display manufacturers. The emergence of high-definition television (HDTV) is adding more fuel to the fire, as are digital playback formats and satellite program distribution. There are many issues to be resolved before e-cinema can take its place in the entertainment mainstream, such as security (how do you protect against unauthorized copying of bitstream-delivered featured films?), and image quality (what bit rate and compression scheme should be used for program delivery?). Until recently, the biggest stumbling block to electronic cinema had been the projectors themselves. It wasn't technically feasible to project large, wide-screen images with brightness, contrast, and color saturation that even came close to 16mm film, let alone 35mm. But that has all changed in the past six years with the introduction of imaging engines based on transmitted light (liquid-crystal displays), reflected light (Digital Light Processing®), and hybrid light-shutter (Image Light Amplifier©) technology. While none of these technologies are ready to replace film immediately, impressive demonstrations of film-like projection quality are being made on a daily basis. Texas Instruments has been busy showcasing standard 4:3, 16:9, and anamorphic 2.35:1 electronic cinema to several studios, using three 1280x1024-pixel digital micromirror devices (DMDs). Hughes-JVC recently announced a joint partnership with QUALCOMM in a new company called CineComm, formed "to replace a century-old tradition of celluloid with an end-to-end digital system" , based on the super-bright ILA-12K cinema-grade projector. It's clear that there is some serious money behind finding and developing an alternative distribution for film-based entertainment. While features and shorts will continue to be shot on film for some time, some will ultimately be converted to digital data and remain in that form all the way to the newest megaplex. This digital data will also be re-purposed for delivery in the home rental market (DVD and other disc delivery systems) as well as eventual broadcast (DTV and HDTV). THE VISION THING As audiences, we crave film projection because it delivers pictures as close to reality as we're likely to get in an "artificial" perceptual environment. With high resolution, random grain, wide contrast, and a seemingly-infinite palette of colors, 35mm motion picture film has set a very high standard for electronic projection systems to hurdle - but they're getting closer with each passing year. With the adoption of high-brightness short-arc xenon lamps and efficient optical paths, the brightness of many high-end electronic projectors is now on a par with conventional film projectors. Improvements in switching speeds, aperture ratios, polarization, and optical coatings have taken electronic projectors from washed-out, flat images just five years ago to rich, contrasty blacks and whites. Fixed-resolution displays such as DMDs and LCDs have now reached over 1000 vertical pixels and are flirting with 1200, while resolution-independent imaging systems like the ILA and the liquid crystal light valve (LCLV) are capable of 1500 and more vertical lines. In terms of brightness, contrast, and resolution, e-cinema projection systems are looking like serious contenders. But there's one last variable to contend with - color. Color is both qualitative and quantitative, and evokes all kinds of responses from different viewers. Artists debate it, printers go crazy trying to match it, art directors argue with post houses about it, companies spend thousands of dollars trying to measure it, and cinematographers and lighting directors devote their careers to manipulating it. Color is a contentious issue for everyone from camera operators to transfer houses, and it's usually due to misunderstandings about how colors are created, the differences between additive and subtractive color, how color palettes (or "spaces") are defined, and how colors are reproduced and viewed. To get a handle on the color quality requirements for electronic cinema, we should take a closer look at the nature of color. COLOR ABCs There are two processes by which colors are created. The first, known as "additive" color, is simply the combination of red, green, and blue (RGB) primaries to achieve a full palette of color shadings. The addition of equal amounts of red, green, and blue results in white light, which we can verify by using a prism to refract these colors back out. Increasing the intensity of each primary color also increases brightness, or luminance. The second color system - "subtractive" color - is the basis for pigments, dyes, and inks. In this system, the addition of all three cyan, magenta, and yellow (CMY) primaries results in black, and the absence of all three colors results in a white image. Increasing the density of each color decreases brightness in a subtractive system. Incident light from sources like the sun and projection lamps is considered additive. However, when light strikes any surface, portions of its color spectra are absorbed or reflected. The reflected light gives us the color of that surface, while the absorbed wavelengths are subtracted. If the surface is an equal-energy reflector, the resulting surface color should have no color impurities. If not, we may see a reddish or bluish tint to the reflected image. (The same holds true for incident light. The sun is an equal-energy light source, containing a fairly "flat" spectral response from red to blue. Artificial lights like metal-halide or tungsten-halogen studio lamps are not and are usually deficient in certain colors.) I NEED MY SPACE The total numbers of colors that exist in any system defines a color space, also known as a color gamut. There are several color spaces/gamuts; each resembling a rough triangle shape. The coordinates for each point of this triangle can be mathematically expressed as x,y coordinates, although the actual appearance of a color space is more like a 3D "anthill" - the third dimension (z-coordinate) being luminance. The number of colors that can be defined within any color space is determined by the maximum shades of gray possible (luminance), along with the three primary colors used to mix and derive other colors. Because the sun is capable of generating an intense amount of both visible and invisible (infrared and ultraviolet) light, its natural color palette - or color space - is by far the widest. In fact, there are millions of natural colors we'll never see, as our eyes are incapable of responding to them. What further complicates matters is the fact that our eyes don't see all colors with equal sensitivity. We are most sensitive to yellowish-green light (59%), followed by red (30%), and blue (11%). This human color response was first plotted in 1931 by the International Commission of Lighting (CIE in French), but also forms the basis of our present-day analog NTSC color television system and the CCIR-601 digital color specification. The 1931 CIE chart was the first to plot specific mathematical values, thereby defining a real, measurable color space. Disappointed to learn there are colors you can't see? Guess what - there are colors you can see, but can't be reproduced on a television monitor! The phosphors used in TV sets (as well as studio monitors) have their own coordinates on the CIE diagram to ensure consistency from one monitor to another. So, we must further truncate our color boundaries in order to stay within a "phosphor-friendly" range. In North America, it's known as the SMPTE 'C' color space. Now we can create any colors we wish for our broadcast electronic images, as long as they are derived from color values contained entirely within these boundaries. This may sound a bit restrictive, but without standardization there would be no way to assure a consistent color match from one monitor to another. Because the SMPTE 'C' space is much smaller than the visible color space, it's virtually impossible to display the saturated colors created by rainbows, prisms, or "pure" coherent light sources like lasers. As television evolves into a digital form, there's a color space to go with it and the current boundaries are determined by the CCIR-601, YUV standards. This system has its roots in the CIE color diagram, with the difference being that colors are determined by digital sampling of luminance and two chrominance signals in a 4:2:2 ratio - not the relative levels of analog voltages. The color space for HDTV - a pure digital format - is also very close to the CCIR-601 and SMPTE 'C' coordinates. It makes sense to use the CCIR-601 color palette for all aspects of electronic media production and display, regardless of whether the final product is shown on television, transferred to disk or tape, or viewed in a theater. The evidence so far is that film-to-601 data transfers - and even 601 data-to-film projects - compare favorably to "pure" film-based colorimetry, assuming the data-to-film transfers are done with tight controls on color consistency. For example, selected screenings of "Saving Private Ryan" this past summer were accompanied by trailers for Reebok and Sony that originated on 35mm stock and were posted as D1 video for national TV spots. Tape House Digital Film in New York took this D1 material, eliminated the 3:2 pulldown and reduced the frame rate to 24 fps, then repositioned the material to 1.85:1 aspect. After checking for any field "glitches", the data was then recorded to film at 2K resolution using proprietary pixel scaling software and conversion from CCIR-601 YUV to RGB color space. The result? Image quality was comparable to any other "Coming Attractions" intermixed with these film-to-digital video-to-data-to-film spots. DROP THAT MOUSE! By definition, the colors which exceed the 75% saturation limits of NTSC are known as "illegal" colors, although you won't get arrested for trying to use them. Print designers and art directors are often frustrated with the inability to reproduce specific CMYK print (subtractive) colors in the CCIR-601/SMPTE 'C' phosphor (additive) space, and often ask for color saturation levels to be boosted to get their special hue. A creative colorist can "jigger" a monitor or play other tricks with color to get a "buy" from a client, but it's a sure bet those colors will never see the light of day when viewed on a conventional video monitor. The reason? "Jiggered" luminance levels will fall outside the SMPTE 'C' space. If you need more saturation in printed color, you add more ink. However, if you increase luminance (and thus saturation) of a video color, you'll run out of head room in the encoded, baseband NTSC video signal. Some examples of "illegal" colors in the NTSC system that also fall outside the SMPTE 'C' color space include turquoise, lime green, indigo, cherry red, and pumpkin orange. (Not coincidentally, all of these shades are located near the very edges of the visible color space.) You may be able to reproduce one or more of these colors on a standard RGB monitor, where saturation levels are dialed in 255 steps and color matching systems like Pantone© are used. But you'd need to transfer the data back to film, or use a dichroic RGB projection system to view 'em. The shift to digital media production is producing many skilled colorists who like to experiment within the precise coordinates of the CCIR-601 color space. By careful tightrope walking along the edge of the SMPTE 'C' curves, the resulting images have an almost "illegal" look with saturated reds and oranges, glowing pastel colors and even something that resembles the seemingly-unattainable turquoise shading. IN THE THICK OF IT To get a better perspective on color spaces and digital media production, I spent a few hours at the Advanced Imaging Center at Tape House in New York City, a busy film-to-digital transfer and HDTV edit/post facility. With its sister digital-to-film operation Tape House Digital Film, AIC creates many spots, trailers, and other projects for both broadcast and theatrical release. AIC installed the first Philips Spirit DATACINE in the world, and is active in data conversion from film to both HDTV and DTV. AIC's vice-president and Spirit DATACINE director John Dowdell III is well-known for his transfers and coloring, producing work for Miramax and Merchant/Ivory Productions, as well as Ken Burns' Baseball, Lewis & Clark and Frank Lloyd Wright miniseries. His transfer suite revolves around Pandora's Pogle color correction system, and the bulk of his work is converting from 35mm negative to 1920x1080 files. "When we work with digital data transfers, we standardize on the 601 color space", said Dowdell. "There's absolute consistency and predictability to staying within that color gamut that facilitates moving from film to data, doing composites, layering effects, and even transferring back to film." The Spirit is capable of 4:4:4 sampling, recording luminance information at 1920 pixels of resolution per line and full-depth RGB color. I viewed a mix of both 35mm and HD footage from a D5 machine using a small Sony VPL-W400Q 16:9 dichroic LCD projector, and there were plenty of saturated colors to be seen. "The Spirit records a much wider gamut of colors than can be seen within the SMPTE 'C' color space", said Dowdell. "You'd need an RGB display to view them, but they're in the data. When files are transferred back to film, all of those colors are retained." This means that a client may not be able to see a desired color, unless an LCD or DLP projector was available. "Pushing the limit on color saturation is a common request in TV spots, like cosmetics", Dowdell commented. "The Spirit has enough pixel sampling depth to bring out more subtle shades of a color, like those seen in lipstick ads. The Spirit's color matrix results in the correct luminance values for each color. We can achieve excellent color saturation and absolute color accuracy." A few blocks away at Tape House Digital Film, David Kuttner, director of research and development, works with a wider color gamut than SMPTE 'C' - his area of concern is transferring data files back to film using Solitaire recorders, and he's currently looking at other high-performance film recording systems. "We use dozens of color look-up tables for our Solitaire film recorders, and we're constantly modifying them to preserve all the colors seen in 601 data files" said Kuttner. "Our calcits monitor the intensity of each color plane. We're also constantly checking film gamma to match the SMPTE 'C' phosphors. It's a never-ending process that involves lots of little tweaks." Kuttner agreed that achieving a "film look" will be the toughest challenge for any electronic cinema system. "Film has a greater color depth than video, and tracks color logarithmically, like the human eye. Any electronic projection system will need to support 36-bit color with 12 bits per color plane. 150:1 contrast will probably the minimum acceptable grayscale, although daylight film stocks can achieve 1,000:1 contrast." The minimum resolution needed to approximate film projection? "Probably a 2K image to be acceptable - 2048x1556 pixels, said Kuttner. "That works out to an enormous file, typically 75 MB per frame. It also provides more color shadings at the low end of the grayscale, key to film-like quality." Considering none of the cinema-quality projectors currently offered for sale use 12-bit RGB processing, that would appear to be the next big hurdle in the evolution of e-cinema. What about viewing colors in a transfer suite? Dowdell uses a BARCO 20" monitor with a MegaCalibrator system for precise color matching, and recently ordered a Digital Projection Power 3gv for projecting footage onto a 9' wide front screen. "The colorimetry of the Power 3gv is the best I've seen. I can get a good match to the 601 color space, plus the digital modulation system results in more accurate grayscale reproduction", he said. "And grayscales are what it's all about, if electronic projection is to approach film projection." RUN THE GAMUT It would appear that the determination of a "standard" color space for film-to-data transfers and eventual electronic projection is emerging by consensus - not edict. There is already a move afoot to push for a 1080p, 24 fps HDTV standard, which would be 100% compatible with film projection and eliminate any need for a 3:2 pull-down in data transfer. The evolution of this particular standard will also be by consensus. And so it goes with color space. Staying within the CCIR-601 color gamut makes sense for another reason: Many cinema-grade electronic projection systems are adding direct serial digital inputs for both D1 and HDTV signal sources, ensuring that colors in the final projected image will match the colors seen in the film-to-data transfers, regardless of how many copies are made or when they are distributed. With the eventual adoption of 10-bit and 12-bit pixel sampling, electronic projection systems will be able to show a far wider and richer palette of colors, helping them close the gap even more with 35mm film projection systems. This article will appear in the February 1999 issue of Millimeter. ©1999 Peter H. Putman / Primedia Intertec