Color Reproduction Complex -1 - JENOPTIK LDT GmbH Andreas Deter Dr. Wolfram Biehlig IPS Valencia 2004
Expanded Color Space Basic terms in colorimetry and color mixing User benefit of laser projection with extended color space -2 -
State in the Art Currently, different types of projectors are used for digital image reproduction in planetariums. These are: CRT LCD DLP Light Valve Laser projection For qualification of projectors, important parameters are: Brightness Contrast, black level Resolution New parameter of increasing significance: Extended Gamut Laser Projection -3 -
Color Space The color table on the right shows all perceivable colors There is an inherent mismatch between any reproduction device and its source All capturing and projection devices have a restricted gamut The gamut of a given device is defined by the location of its three primaries red, green and blue y 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 510 505 500 495 515 490 485 520 530 540 550 560 570 580 590 600 610 620 640 700 0,1 480 470 460 400 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 x -4 -
Color Generation All colors are produced by superposition of the primaries The color triangle is defined by the spectrum of the primaries -5 -
Color Generation in CRT, DLP, LCD 100 CRT Phosphores make up color capabilities CRT-phosphores: broadband emission 75 50 25 LCD / DLP Light source: white light (UHP-lamp) Use of filters for color generation Filter design is a compromise between luminance and bandwidth 0 400 450 500 550 600 650 700 blau 459 nm grün 558 nm - dominante Wellenlängen - rot 612 nm The srgb triangle: 33 per cent of the whole visible region -6 -
Color Generation In Laser Projection intensity Unlike conventional projection devices, this projector uses three monochromatic colors The color triangle covers about 65 per cent of total table area Picture brilliance increases with color saturation Highly saturated colors are less effected by ambient room light 67,9 %95,3 % 100 % power proportions related to D 65 400 446 532 629 700 wavelength (nm) -7 -
Color Transformation for Laser Projection Simplified signal chain in laser projection: Necessary preconditions: unchanged picture colors, realistic colors Realtime processing Color transformation can be turned on/off fast and easily video source video source primaries laser primaries picture R G B color transformation on laser laser laser = 0,3 0,4 0,3 0,5 0,4 0,3 0,2 R 0,2 G 0,4 B source source source color transformation off R G B laser laser laser = 1 0 0 0 1 0 0 R 0 G 1 B source source source Laser Colors -8 -
Contrast Physiological properties of the human eye: Perceives differences in luminance (contrast) luminance not so important High contrast is necessary for high color saturation (colorfullness) In many cases, high contrast produces a quasi 3-D effect -9 -
Influence of Projection Lens System Object What matters is the quality of the imaging process (Modulation Transfer Function MTF) Lens Image Object Lens: imaging process Image - 10 -
Extended Color Space From a User s Point of View How can users profit from an extended color space? What data and contents can he/she use? How should future action look like? - 11 -
Utilization of Extended Color Space There are no generally established methods as yet Despite that, users of laser projectors can benefit from an extended color space already today Method selection essentially depends on the type of available data source Data sources: - Computer-generated data - Working with preexisting image contents - Resampling of color film material - Image contents captured using an extended color space (camera) At the moment, only laser projectors are capable of reproducing strongly saturated colors correctly Color data can be displayed on control monitors, but this may imply some color shifts - 12 -
Computer-Generated Data The image contents for planetarium applications are largely generated on graphic computers. Natural colors need not be rendered in a realistic style Data bases maintained in Image Generators (IG) Integrated digitzed image contents Visualization and animation files, virtual reality Graphical effects - 13 -
Methods: Computer-Generated Dates a) Interactive generation of image contents with laser projector Internal color transformation function is turned off Colors are defined and assigned in accordance with visual image perception of viewer Correct color representation only possible with laser projector Laser Colors - 14 -
Methods: Computer-Generated Data b) Use of desaturated color gamut Image contents are developed at the monitor with desaturated colors (unchanged hue) Maximal saturation on display screen corresponds to max. projector saturation White remains white Relative degree of saturation is preserved - 15 -
Methods: Preexisting Image Data a) Switching from srgb to laser color space Internal color transformation is turned off This option can be used with most of the image contents Images appear more brilliant and colorful in the viewer s perception A certain shift in colors has no disturbing effect in the majority of cases Option for online switching to srgb in the event of critical image contents b) Increasing color saturation Operating software provides a controller to increase color saturation This allows the prevention of hue-shift effects c) Mathematical algorithms for color spreading Not yet commercially available Selective color spreading is achieved through specified calculation procedures - 16 -
Methods: Resampling of Color Films Available color film material is digitized in extended color space, so far limited to CRT gamut Color films account for 50% of maximal color space Color science is required to develop new gamut mapping methods Methods: Image Contents Recorded in Extended Color Space Currently, development work is underway for image capturing devices (multi spectral technics) to directly record a given image contents in extended color space mode A second design step will address gamut mapping that is matched to the laser gamut (RGB) Suitable data formats shall be provided for direct representation of image contents; color transformation is turned off - 17 -
Extended Color Space Benefits Now available with laser projektion Maximal saturation of colors Lifelike colors Better visualization possibilities Very high contrast Scientific effects Makes the invisible visible Dives into new depths High diversity of presentable information Light going new ways! - 18 -
Thank You For Your Attention! - 19 -