Secrets of the Studio TELEVISION CAMERAS Technology and Practise Part 1 Chris Phillips
Television Cameras Origins in Film Television Principles Camera Technology Studio Line-up Developments Questions of Colour
My Background RAF Electronics technician Airfields BBC Studio Engineer TV Centre Attachment as Vision Operator News and Current Affairs Sony Consumer Products Engineering Officer Further Education College Electronics technician, part-time lecturing Panasonic Broadcast UK Technical Trainer DVCPRO digital video tape training Babcock International Electronics lecturer
Origins in Film Movie camera takes a rapid sequence of photographs on strips of film Each image is a "frame" Accomplished through an intermittent mechanism Initially limitations: Cranking speed Sensitivity of film
Projection Frames played back in a movie projector at a specific speed, frame rate (frames per second) Eyes and brain merge separate pictures together to create the illusion of motion Author: Joram van Hartingsveldt 2006 Typically 24 fps Flicker reduced by dual or triple blade shutter Effective 48 or 72 fps
Television principles Each frame is scanned by a raster Image is divided into horizontal lines Brightness information is converted into video signal Line video waveforms are sent to transmitter sequentially UK transmission 1936 VHF 405 lines 1964 UHF 625 lines
Image scanning 1984 Plumbicon tube uses electron beam to scan image sensor Deflection coils control beam position by magnetic fields Needs regular alignment [Replaced in 1990s by solid state CCD sensors] CCD sensor
Frame rate UK Television Picture Frequency is 25Hz To reduce flicker Interlace Scanning used Alternate lines scanned as consecutive Fields Frame = alternate Odd and Even fields of 312.5 lines Field Frequency = 50Hz Mains frequency once used to synchronize fields (405)
Television receiver Cathode Ray Tube (CRT) was original display method Electron beam scanned across tube face Replaced by Plasma/ LCD/ LED technology Colour uses R,G and B phosphors or pixels
TV Luminance signal Peak white (0.7V) Black level (0V) defined Cameras and monitors are calibrated Picture quality depends on maintaining these Line, frame and blanking pulses are added, to synchronize camera and receiver Flyback occurs during blanking
Lift and Gain GAIN controls highlight detail (mainly lens iris) LIFT controls picture detail in shadows Compensates for scene reflections & lens flare Vision operator manually controls all studio cameras Engineer has override control LIFT GAIN Operation Control Panel (OCP)
Colour Human eye relative sensitivity to 3 primary colours Photopic curve shows relative response at all wavelengths 11% B + 59% G + 30% R = white light Brain adapts to different colour temperatures Sensitivity 400 500 600 700 Wavelength (nanometres) Photopic sensitivity curve
Colour temperature Sunlight higher colour temp (more blue) Tungsten lower temp (more red) White balance achieved by equalising RGB for a neutral target Test chart BBC64 Studio Camera Line-up Test Chart 5800K Sunlight 2850K Tungsten lamp Wavelength (nanometres)
Colour Light split into 3 primary colours by dichroic block R,G and B channels are processed separately until final signal stage R + G + B = white Alignment of images (registration) is very critical Alternative beam splitters
Test Signals Calibrating video path to ensure consistency Monitors, video recorders Picture quality evaluated by monitors Colour Bars
Alignment procedure Standard Studio Camera Lineup Test Chart Tungsten line-up light adjusted to standard lux and Kelvin values Before rehearsal, recording or transmission Camera channels lined up at Camera Control Unit (CCU) Super-black Gregory Hole BBC64 Studio Camera Line-up Test Chart
Link 125 Camera Camera tubes and deflection system Schneider Lens Signal processing Camera Control Unit (CCU)
Solid State Cameras In early 1990s CCD and CMOS sensors finally displace tube cameras Advantages: no image lag superior picture quality better noise-to-picture ratio smaller size and weight, lower power needs CCD dichroic block Reduced alignment time Greyscale and matching No registration errors Little engineering satisfaction!
HD Television In mid 1990s Digital TV is introduced HD cameras were being tested during 90s During past 10 years HDTV has reached our screens?
CCD sensor technology Charge-coupled device (CCD) is divided into lightsensitive areas (pixels) Used to build image of scene; light converted to electrons (charge) Charge is proportional to intensity of scene at pixel Voltages on electrodes guide charge thru silicon
Questions of Colour Part 2
Question of Colour Sensitivity Human eye photopic response Peaks at 550nm (green/yellow) 400 500 600 700 Wavelength (nm)
Question of Colour Is there a mismatch? Human eye photopic response Eye response peaks where sun is maximum Peaks at 550nm (green/yellow) Is it logical if we evolved under the current spectrum?
Question of Colour
Question of Colour Is there a mismatch? Why are most leaves green? Chlorophyll reflects Green light & absorbs Red & Blue But Sun s peak energy in Green!
Purple Dawn? Ancient Man reported purple dawn of Creation Was our star more Red /Blue in ancient times? Did fauna and flora evolve in a different environment?
Questions email: cigarshaped@ntlworld.com