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SECTION: 6.10 is for an overview of the subject of Digital Cinema. See also the program files in the current distribution of my programs, the other parts of this HTML documentation, and the current On-Line version of this Web site for information more specifically about my programs. Any comparisons of my programs or methods to some others is only given as a vague generality of my opinion and is not intended as a recommendation or reference to any particular products, always make your own evaluations and comparisons before taking any action.

A Digital Cinema Camera is a digital version of a film type movie camera. Rather than shoot frame images onto movie film in long rolls that move at high speed through the movie film camera, the Digital Cinema Camera shoots high resolution digital frame images at very high bandwidth into high speed GB or TB size solid state memory or harddrive arrays.

True Digital Cinema Cameras save RAW sensor data for each of the image frames shot rather than use video like compression modes to reduce the bandwidth required and the storage size required. Some hybrid cameras are sold as Digital Cinema type cameras that save the Bayer filter de-mosaic (de-Bayer) image processing step until after compressing, and offer a pseudo RAW image for computer processing, but the artifacts of compression cannot be fully removed and such cameras cannot reach the full quality of a true RAW mode Digital Cinema Camera, although how much those artifacts detract from the later use of the image depends on what the end result is viewed and the quality of the original exposure since poor lighting conditions tend to make some kinds of compression artifacts look worse.

A Digital Cinema Camera runs at variable frame rates just like a film movie camera, rather than just fixed frame rates like a video camera. Since movie film runs at 24fps, Digital Cinema Cameras should also be able to run at 24fps (twenty four frame images each second). Because of the issue of NTSC video frame rates being 1000/1001 times the whole number frame rate, Digital Cinema Cameras should also support 23.97602398+fps so that the running time and sound pitch will come out correct when used for television release and production. Other frame rates slower or faster than the sync sound frame rates allow for under- cranked fast motion and over-cranked slow motion when the digital images are viewed.

Digital Cinema Cameras should accept movie camera type lenses in order to get the same look to the images that you would get from shooting movie film. Because of the need to use movie camera lenses some Digital Cinema Cameras use a sensor that has a Bayer checker board mosaic filter on it. A Bayer filter has twice as many Green pixels as Red and Blue pixels, so the resolution of the Red and Blue are both about one forth what the Green or Luma resolution comes out to be. Because of the problem of chroma moire when using a Bayer filter sensor, an OLPF (Optical Low Pass Filter) is put between the lens and the Bayer filter color sensor to slightly blur the image so that image details cannot just shine on a single pixel in the sensor giving a false color signal. The effect of the OLPF is to divide the image into four superimposed images that spread the image details over groups of four pixel sensors. To overcome the blur of the OLPF image sharpening is done by the de-mosaic (de-Bayer) software that is used after the camera frames are downloaded from the Digital Cinema Camera's storage. Because of the way the OLPF blurs the light going to the sensor some sub-pixel resolution may be disrupted.

Digital Cinema Cameras also can use three sensor chips, one each for the primary colors, rather than a single Bayer filter sensor. There is some debate as to which sensor type, one Bayer vs. three for Red, Green, and Blue make the better images. It should be possible to make a three sensor camera that gives better color than a Bayer sensor camera (because you can better control the dyes used in the filters and reduce the red pickup by the blue sensors etc.), but in real world cameras the extra prisms required to split the images for three chip cameras can introduce chromatic aberrations or rainbow fringe, and it can be very hard to attach the three sensors to the prism array accurate enough to have the colored pixels line up without small errors. The Bayer sensor does not have the alignment issues since its filter is right on top of the sensors, but the color quality and saturation of its filters is not as high as the three chip camera can have so the color quality results from Bayer sensors may be a little off, although with very good de-mosaic (de-Bayer) software and careful color correction of the RAW sensor data and good lighting and lenses Bayer filter cameras can produce good quality images, and Bayer filter cameras can use large aperture cinema type lenses.

There are some optical issues with Bayer filter sensors using older movie camera lenses that were not corrected for the thickness of the OLPF filter and the sensor cover glass. At larger aperture openings some additional aberrations can be introduced by the thickness of a glass or transparent "plate" behind a lens, these aberrations can cause a small shift in the "best focus" making the lens markings a little off so you cannot focus by tape measure without shifting the footage marks one way or the other just a little, and the focus shift would vary with the f/stop being used. For the most part the thickness of the OLPF only becomes an issue at large apertures, and how bad it becomes depends on the thickness of the OLPF and sensor cover glass and the type and brand of lens used.

Because sensors used in Digital Cinema Cameras are IR or Infrared sensitive and in Bayer filter cameras the Bayer filter can pass some IR or Infrared light an IR blocking filter needs to be used. Some cameras may have a built in IR blocking filter with their OLPF filter, but when you use ND (Neutral Density or Dark Gray) filters to control the exposure and f/stop or T/stop of the lens the ND filter blocks the visible light but some ND filters pass much of the IR light so you need an external IR blocking filter in front of your ND filters to prevent color shifts in the cameras images do to IR light getting through to the sensor (subjects are different colors in IR light than visible light, lighter or darker). In other words when you put a ND filter on the camera and open up the lens iris you get constant visible light, but the IR light increases since you opened the lens iris and the ND may not block as much IR as visible light so the IR increases in ratio and causes more color shift through the Bayer filters than when shooting without the ND filter. There are two kinds of IR blocking filters, ones that absorb IR light and ones the reflect IR light. The ones that reflect IR light are called interference filters and have many thin layers that cause IR light to bounce back but let visible light from middle red wavelengths and shorter to just before Violet and UV pass through. Because the thickness of the layers is important to interference filters, when light hits the filter from a side angle rather than from perpendicular the wave length they effect changes, the importance of that is that if you use a reflective IR filter in front of a wide angle camera lens the edges of the image will not be filtered the same as the center of the frame. The type of IR block filter that absorbs the IR light (e.g. heat absorbing greenish glass) does not have the wide angle lens problem, but does not have as sharp a cut off above red light and both cuts red light and passes some near red IR light, so may let some color shift due to IR happen in addition to its sometimes greenish cast that would need to be color corrected out of the images later. Some ND filters are not made of dyes that pass IR but are semi-mirrored glass, from the back you see a dark-gray image through the filter, but from the front you see yourself in the filter like a mirror. Although the mirrored ND filters are good for their also cutting IR light along with the visible light, you need to be careful to put the mirrored side out and to have the mirrored filter in the front (side closest to the actor) of your matte box set of filter holders since you can get reflections that may show up in your images if the other filters start to bounce light around between the filters. The same goes true with the interference filters, you should put the IR mirror side toward the subject to reduce reflections between the filter stack.

Because many Digital Cinema Cameras are near Daylight balanced, rather than the tungsten balance used for some movie film negative stocks, when you are shooting under light sources less than Daylight K values you should use a Wratten 80 series bluish filter to bring the light entering the camera up to the natural balance of the Red and Blue sensors. Although video cameras use electronic gain on the Blue sensors to correct for low K value light sources, when shooting Digital Cinema you want to preserve the maximum dynamic range and to reduce the sensor noise to its minimum, if you do white balance by raising the gain in the sensor you increase noise and reduce dynamic range. Using Wratten 80 series filters can result in a two stop loss of EI rating for the camera, so some camera manufactures may not suggest using optical filters to maximize the image quality and dynamic range. Also the Green sensors may have a natural sensitivity higher than the Red and or Blue sensors, even in Daylight, this makes the Green sensors white clip before the Red and Blue sensors for bright areas of the image in normal use. To prevent the uneven white clipping and off color highlights you can use Magenta CC filter in front of the Digital Cinema Camera to balance the three color sensors exactly so that the de-mosaic (de-Bayer) software does not need to clip the other two colors lower down to match the higher one (or raise their gains which is about the same as lower clipping.) To try to improve the color quality a three bandpass filter like the XB29 (tm) filter can be used to filter out UV, Cyan, Yellow, and IR, using a multi-band optical filter may be better than adjusting the chroma matrix settings in the de-mosaic (de-Bayer) software since a cleaner signal generally gives better results than a noisy signal that is signal processed. The XB29 (tm) filter does have the issue of being an interference filter and so might not work well with wide angle lenses. For use with wide angle lenses a special type of glass with minerals in it can be used since it works at wide angles, such filters are sold as a "color enhancing" filter for movie cameras and absorb Yellow light making the separation between green and red greater.

Because Digital Cinema Cameras store many frames in their storage, some time is required to download the frames shot into a computer for editing and color correction. The computers used for editing and color correction need to be fast and have a great deal of storage. The size of the Digital Cinema Camera frame images depends on the resolution the Digital Cinema Camera is set to for recording, but perhaps the minimum image size used would be 2048x1152 to try to meet the DCI standards for Digital Cinema projection in theatres (the 2048x1152 images would be letterboxed into the standard 2048x1556 frame sizes, note that the 2K DCI standard is 2048x1556 pixels rather than the 4:3 ratio 2048x1536 used for computer graphics).

Other than the use of Digital Image capture Digital Cinema Camera can use the same accessories used by film type movie cameras, that is a matte box, a follow focus, eye light, lenses, filters, and so on. In fact to get "film like" images using the same accessories, lenses and optical filters is just about required since those accessories are what give film its "filmlook" in the first place in addition to the films natural diffusion of the images due to its being particles suspended in gelatin.

The exposure of Digital Cinema Cameras is more critical than a film based movie camera since the sensor hard clips the white points where as film has a softer cutoff on the over exposed parts of the images. So in addition to using a light meter to set the lens iris, ND filter, and shutter opening angle, histogram display and video type waveform displays are used to check for over exposure of the sensor. To check for under exposure the Digital Cinema Cameras have an electronic viewfinder that is gamma corrected to brighten the shadow areas letting you see the noise level in the shadow areas, if you have too much noise in the shadow areas you need to add fill light since if you open the lens up you will get overexposed highlights. When you cannot control the lighting you may be able to go to a longer focal length lens to exclude the areas of the image (background, sky, lamps, etc.) that are too light or dark too correct later from the RAW sensor data frame images in the color correction step of DI workflow.

You can find more information about using my programs for Digital Cinema tasks by looking in the sections that have the text from the program and update documentation files corresponding to the documentation files in the ZIP archive files for the program executables from the Download sections. See SECTION: 3.80.0.0 for information about using DANCINEL.EXE (tm) in a DIY film recorder, see SECTION: 3.85.0.0 for information about using DANCINES.EXE (tm) in a DIY film scanner, and see SECTION: 3.3.7.34 for information about using DANCAD3D.EXE (tm) and DANCAD87.EXE v3.7N+(tm) for motion picture post production and DI (Digital Intermediate) to edit, color correct, and sound mix a feature motion picture. See also any later Update files relating to the programs, and look in the Downloads sub-sections for additional utilities and or programs that may be added that relate to Digital Cinema.