Inside Thermal Imaging Camera

     This post deals about components of infrared camera system. Infrared region ranges from 0.7 μm to 1000 μm. For convenience infrared is split into shortwave (3 to 5 μm) and longwave (8 to 12 μm) bands [1].  Few types of thermal camera are shown in Figure 1. Their appearance will be similar to conventional cameras.                                 

Figure 1. Various types of Thermal Imaging Cameras Courtesy ref. [3]

In ambient temperature, radiant flux emitted by is more in longwave than shortwave. But shortwave is more sensitive to longwave at ambient temperature conditions. Sun radiation is small but significant in shortwave range. It is helpful to increase image contrast in some cases and in cases like measuring temperature of an object, sun radiation is unwanted. Longer wavelength can penetrate mist and smoke better than shortwave. So longwave always preferred in surveillance applications.

            At cursory level, architecture of thermal cameras will be similar to conventional cameras. The main differences are presence of scanning subsystem and cooling subsystem.  The schematic diagram is shown in Figure 2. The IR rays from object are focused on detector or detector array through IR lens. In detector IR to electrical signal conversion takes place. Readout circuits transfer the electrical signals to storage devices and display devices.

(i) Lens: Functionally Infrared and visible range lenses are same i.e. they perform same duty irrespective of the spectrum in which they operate. But Infrared lens materials have relatively higher refractive index than visible spectrum lens. For example germanium has refractive index of 4.01 at 10 mm compared glass which is having a refractive index of 1.5 at optical spectrum.

(ii) Scanning system:  This subsystem is missing in conventional cameras. Purpose of the scanning is to transfer image formed in the lens to the detector or detector array in well controlled fashion. The types of scanning systems are as follows; object space scanner, image space scanner, and afocal scanner. For detailed information refer [2].

(iii) Detector: It is the most important component in the entire thermal camera. Thermal detector and photon detector are the two types of detectors. In thermal detector, IR radiation heats the detector element and this in turn change in physical characteristics (for example, electrical polarization or resistance). This change in characteristics is measured.

In photon detector, electron absorbs the photon that comes from IR radiation and the electron jumps form one quantum level to another. It is more sensitive than thermal detectors. To have better performance quantum detector has to be cooled. This facilitates photons–electron interaction. Photon detectors are constructed using semiconductors. Either they act as photoconductors or photovoltaic devices. In photoconductor absorbed photons moves a valence band electron into conduction band and there by increasing the conductivity of device. As name suggests absorbed photon generates voltage in the p-n junction.  Shortwave detectors need to be cooled up to 195K but long wave has to be cooled up to 77 K.  This is the temperature of liquid nitrogen. (I strongly believe liquid nitrogen it is flammable)

They are mainly three types of photon detectors are available.

• (a) Cadmium mercury telluride (CMT): By changing the composition it can be made to operate in longwave or shortwave band.
• (b) Indium antimonide (InSb): It is used in shortwave band only. It can be constructed to operate as photovoltaic device or photoconductive device. For get best performance it has to be operated in liquid nitrogen temperature.
• (c) Platinum Silicide (PtSi): This detector functions as Schottky barrier photodiode. It works in shortwave but with 77K temperature. It has very poor quantum efficiency. Only two percentage of incident photons are converted. It is well suited for arrays only. This material is well compatible with the readout circuit.

(iv) Detector Arrays:  Development of thermal arrays is relatively recent and possible as a result of MEMS(micro-electromechanical systems) technology.

• (a) Pyrovidicon: This can effectively function in longwave band. Now this imaging device has become an historical interest. It functions similar vidicon video camera. But the detector is infrared sensitive.
• (b) Resistive bolometer arrays: This is very popular array structure. Here temperature is proportional to change in resistance. It is made of top temperature sensitive resistive layer and bottom layer that contains read-out circuit. These two layers are connected by pillars. The air gap between two layers acts as a thermal insulator. These types of bolometers incorporate coolers to maintain an optimum temperature that is conducive to resistive element and the readout electronics.
• (c) Ferroelectric/pyroelectric arrays: Construction-wise it is similar to resistive bolometer arrays, except the detection is based the pyroelectric or ferroelectric effect. Pyroelectric material become electrically polarized when there is change in temperature. This in turn generates charges and resistance of the top layer (resistive layer) goes down. A typical example for pyroelectic material is trigycine sulfate (TGS).
• (d) Bimetallic Cantilever Arrays:  It has two layers and both of them hinges on capacitance measuring circuit as in Figure 2. Top layer is made up of gold bimetal and consists of IR sensitive film. This layer is supported by SiO substrate. Top layer and bottom layer is separated by air gap. As both layers are metal and in between air is insulator it forms a capacitor. When infrared falls on the film, top layer bends towards the bottom layer. This change of physical arrangement causes capacitance to vary. This variation is measured.

• Staring array configuration: Thermal sensitivity of an imager can be improved if the effective imaging areas of the detector elements are increased. (Please note entire area of the detector is not occupied by imaging section of detector element. For example, in the bimetallic cantilever array only small portion of top cantilever is filled with IR sensitive film). Size of the detector elements must be limited to maximize spatial resolution of detector arrays. Various configurations are proposed and adopted in cameras, out of which staring array is very popular and deployed extensively [2].

(v) Cooling subsystems:

Most of thermal cameras employ cooling or temperature control for optimal performance. There are four types of cooling methods are used widely.

• (a) Bulk cooling: It is the simplest cooling method. Here detector is placed inside the Dewar (Flasks ?) and later is filled with liquefied nitrogen. It is well suited for laboratory purposes.
• (b) Thermoelectic cooler (Peltier cooler):  It is based on Seeback or Peltier effect. Current flowing through a junction of two dissimilar materials produces a change in temperature at junction. Direction of current flow decides whether the junction to be cool or hot. With this arrangement temperature up to -40K is achieved.
• Other two coolers are Joule –Thomson cooler and Stirling engine coolers.

(vi) Processing Electronics and Display:

The generated voltage or current has to be read out, conditioned (amplified and A to D converted) and stored in a memory. Major problem is making an electrical connection to each and every detector element. To reduce number of external connections, on-chip signal processing has to be carried out. This strategy is already employed in CMOS and CCD arrays.  Maximum resolution of thermal cameras will be 300x300. So LCD displays will be very sufficient.

Source:

1. IR Thermography Primer, FLIR Systems Co. Ltd, http://www.termogram.cz/pdf/thermography_primer.pdf, (749 KB, PDF)
2.  Thomas L. Williams, Thermal Imaging Cameras: Characteristics and Performance. CRC Press, 2009.
3. Thermal imaging guidebook for industrial applications, FLIR Systems AB,  http://www.flirmedia.com/MMC/THG/Brochures/T820264/T820264_EN.pdf  (2014 KB, PDF).

Thermal Imaging - I

Infrared is a range of electromagnetic waves that lies just below visible spectrum and above the microwave spectrum. As it lies below the red colour, it got its name. Wavelength of these rays ranges from 700 nm to 1000 micrometer. Like visible light these rays can be emitted, reflected and absorbed. These rays cannot be seen but it can be felt as our skin is sensitive to temperature. Any object that is above -273.15 degree Celsius or 0 degree Kelvin can act as a source of infrared radiation. That means an ice cube that is cold will also emit infrared radiation. Sir Frederick William Herschel discovered existence of infrared in the year 1800, when he was studying radiations from Sun. In 1900 Max Planck gave the governing laws behind the thermal radiation. For convenience infrared is split into shortwave (3 to 5 micrometer) and longwave (8 to 12 micrometer) [1].

In 1970 commercial grade thermal camera arrived for market. These cameras were bulky with several components. They required liquid nitrogen to cool the system. Typical example for this type camera is AGA Thermovision 660 [2]. Within 10 years size of camera reduced considerably. Now uncooled micro bolometer based infrared cameras are available. They look like visible camera i.e. conventional digital camera.

As for as working of thermal camera is concerned, is very similar to visible cameras. Infrared camera optics is focused on an object-of-interest and its heat signals are captured by detector. The detector is read row-wise and outputs are got in the form of voltage. Then A-to-D converters map the voltages into numbers. As infrared is invisible they don’t have inherent colour. So, false colours used and they are mapped to the data range to produce a thermal image. This is shown in LCD screen that is present in the camera. These images can be stored in memory cards.

Dissimilarities

1. First is pixel count. A low end camera will contain 4 million pixels as compared to high end thermal camera that may contain 3 lakh (0.3 million) pixels. 
2. A low end thermal cameras cost around $6000 US dollars [3] or 3 lakhs Indian rupees.
3. Primary objective of thermal camera is to measure heat and record from every point of the object. Professionals are required to take a useful thermal image. They are expected to know the physics behind the thermal imaging and should have the ability to interpret the thermal images properly. Put in simpler terms it is a measurement tool. In contrast digital cameras are used to freeze important moments in life. So visible cameras are designed to be operated by everyone and shoot pictures with ease.
4. A thermal image is always accompanied with visible picture. As thermal image is radiometric one, it should be always accompanied by a temperature scale (a bar that contains the colours used in the image along with corresponding temperature. This can be seen in Figure 2 thermal image). Thermal fusion images are optional but they are very informative. Please refer figure 1. For more images refer [1, 2].
5. Infrared images use, false colour palettes like gray rainbow, iron. 

Night vision camera and infrared thermometer are sounds similar to infrared camera. Night vision camera requires very minimum visible light (moon light) and near infrared to capture image. A novice will mistook output of night vision camera as from infrared camera. Figure 2 will help to understand the difference. Infrared thermometer will capture temperature of particular spot i.e. pixel resolution is one pixel only. Any low end infrared thermal cameras will posses 3600 pixel resolution. 

Figure 2. Difference between visible, night vision and thermal infrared images

Applications

Few important applications of thermal imaging are electrical installations, machineries, thermal insulation inspections in buildings as well as in heat conducting pipes and flare detection. Thermal images can be used in medical diagnostics also. It is mainly used to detect breast cancer tissues. Thermal images are used to visualize the level of injury in the body. Medical related thermal images will not be discussed in this post. Refer [4] for other areas applications like sports, veterinary, music and dance.

Thermal cameras are primarily used as non-invasive testing equipments. Non-invasive testing is very popular for two reasons. It can be used in preventive maintenance and is very economical. Today all the machineries present in factories run 24x7 and throughout the year almost without break to produce cost effective products. Wear and tear and associated failure is natural in any machinery. Problem of occurrence of failure is avoided with preventive maintenance.

Greatest beneficiary of thermal imaging is inspection of electrical systems. They are classified into high-voltage installations and low-voltage systems. First generation thermal cameras were primarily used to inspect high voltage power lines. Corrosion in electrical connections in high-voltage installations increases resistance. This causes rapid rise in temperature and subsequent meltdown or breakdown of connections. Outcome of this will be unplanned outages and fire hazard. Electrical short-circuit is a major cause of fire in buildings, factories and godowns. Fires destroy materials worth of billion dollars in a year. 

It is a common knowledge, when a moving part in equipment is misaligned or malfunctioning then it will produce heat, later it manifest itself in excess vibration and in extreme condition it produces sound. As the first symptom of malfunction i.e. rise of temperature cannot be detected by conventional means, we rely on secondary symptoms like vibration or sound. For example, in mechanical systems like conveyor belts worn out of rollers can be easily detected using thermal imaging. Some of the problems like motor failures due to brush contact-wear and armature shorts produce excess heat only. They go undetected by vibration analysis.

Building inspection: Western countries reel under severe winter and to make life comfortable houses use central heating systems. If walls and windows of the building are properly insulated then heat will seep through them. At summer, places like in Middle East and India will reel under excess heat. To combat this centralized air-conditioning systems are used. If the house is not properly insulated then heat will seep through walls and reduce the efficiency of cooling system. Thus thermal images of house are used to find out insulation efficiency of house. Properly insulated houses require less energy to cool or warm them. Thus it leads to lot of savings. Same holds good for pipes that conduct steam and cold liquids. 

Infrared camera fitted with protective filters can see through flames. This helps a lot for fire fighters to look beyond flames and take appropriate rescue operation. In certain industries like petroleum refineries harmful gasses are generated and they should be burned off in flares to avoid environmental degradation. Normally these gasses are invisible to naked eye. Thermal images of chimney will show whether gasses burned or not.

The last but not the least application is to teach physics. The interaction between walking person shoes with floor can be captured in thermal camera in video mode. The footage will help students to see the frictional force and visualize its effects. A basketball that falls on the floor will get deformed for brief moment and its temperature will rise. A high-speed thermal video footage will help student to see rather than to believe teachers’ lecture [4]. 

Note

o Ref. 1 contains 28 pages. It is very interesting to read and has good amount of illustrations to convey concepts. 

o Please search for thermal image videos in youtube.  I hope it will really help us.

Source

1. IR Thermography Primer, FLIR Systems Co. Ltd, http://www.termogram.cz/pdf/thermography_primer.pdf, (749 KB, PDF)

2. Thermal imaging guidebook for industrial applications, FLIR Systems AB, http://www.flirmedia.com/MMC/THG/Brochures/T820264/T820264_EN.pdf, (2014 KB, PDF)

3. B.R. Lyon Jr., R.J. Rogers, Techniques, “Tips and Tricks: Operating a Modern Radiometric Thermal Imaging Camera,” Presentation handout of ASNT 2007 Fall Conference, Las Vegas, USA, Nov. 14, 2007. 

http://www.hvacexcellence.org/nhetc/archive/2011/documents/downloads/flir.pdf, (7383 KB, PDF)

4. M. Vollmer and Klaus-Peter Möllmann, Infrared Thermal Imaging: Fundamentals, Research and Applications, Wiley-VCH Verlag GmbH & Co., Germany 2010.

Digital Cinema Projection Technologies

         Digital Cinema projectors are the last and most important component in the Digital Cinema system. In the 100 year history of cinema lot of advances came through in cameras, lenses, widescreen movies, audio and so on. But projectors remained unchanged for very long time. “Star Wars” movie was a trend setter. It was shot in digital camera and it was projected using digital projectors [1]. This was a real break through.  In the world there are around one lakh (100 thousand) cinema screens are there and around 6000 screens are converted into digital every year [2].  Projection technologies can be broadly classified into three categories; Digital Light Processing (DLP), Liquid Crystal on Silicon (LCoS) and Grating Light Valve (GLV). DLP technology from Texas Instruments (TI) is the only successful commercial product until up to 2007. It will be dealt in detail in this post.

Projection system is a combination of projector and cinema screen which is made up of silver halide. That is why movie theatres are referred as silver screens [citation reqd]. Light from the projector falls on the screen and incident light is reflected and it is viewed by patrons (a respectful term for movie goers). It is expected the entire projection system is in dark enclosure. Any stray light inside theatre will have a detrimental effect on projection system performance. But in TV light is emitted and room with minimal illumination is a requirement.

All projection system will contain following components; light source, light splitter, light modulator, light combiner and projection lens. For block diagrams of projection systems refer [2]. Normally light source will be Xenon arc lamp that can emit red to long wavelength blue with equal intensity. This lamps will consume 1200 W to 6500 W, operating voltage will be around 20 V to 33 V and current rating range from 60 A to 120 A. The power consumption of projection unit will be much higher than arc lamp. The life span of lamp will be around 2000 hours.  Laser is very power efficient but laser based GLV has to become commercially successful. Dichroic mirrors (wavelength selective) or similar devices split the light into red, green, and blue and send them to three light modulators. The light modulator is the real heart of the projector. It changes the incoming light amplitude depending upon pixel value. This operation is called modulation. As we know colour pixel is made up red, green and blue channels and each channel when viewed separately will look like a gray scale image. Thus if the incoming light is blue then output from light modulator will be from darkest blue to lightest blue. Modulated red, green and blue lights are overlaid by the light combiner (prism arrangement) to produce the desired image.  The projection lens will project the image into the screen. Everyone would have noticed that projection booth is above from the center of the screen. This means the projector sends the light downward to project it on the screen. This introduces  trapezoidal distortion to the image and it is rectified by using trapezoidal mask in the aperture of the projector [3].

Figure 1.  A typical theatre arrangement

1.  DLP Light modulator

It was developed by TI who is a leading player in semiconductor industry.  Jack Kilby who got Noble prize in 2000, for inventing Integrated Circuits (IC) has served Texas Instruments. Digital Micromirror Device (DMD) is the heart of DLP. It was developed in 1977 and in 1990 only it came out of R&D cocoon [1]. Size of the DMD will be around one square inch and it contains 13 lakh (1.3 million) aluminum micro mirrors. They are hinged to the CMOS surface of the IC and mirrors can be tilted 5000 times within a second. Three DMDs are used and each DMD is allotted to one primary colour (red, green, blue). One DMD with colour wheel can be used instead of 3-DMD arrangement. With this arrangement projected image quality and reliability of the system take a beating.

Figure 2.  Leg of an Antenna in the backdrop of DMD mirrors

Each DMD mirror occupies an area of 16 micro square metre.  The underlying CMOS circuits acts as an actuator and tilt the mirror by either +10 degrees or -10 degrees [4]. Thus when the mirror is tilted +10 degrees illumination light is turned away from projection lens. At -10 degrees illumination light is sent into the projection lens. Thus there is only ‘on’ and ‘off’ states only. With this kind of binary systems how colour images are projected onto the screen is the question that arises in our mind. Our human eye is fooled by flipping mirrors in three light modulators very quickly so that our integrating eye sees the colour. This process uses pulse width modulation. Manufacturers Barco and Christie  are licenced to produce TI DLP projection systems. NEC is also building digital cinema projectors using DLP.

2.  LCoS Light modulator

It sounds like LCD and it share lot of similarity between LCD. Earlier to LCoS transmissive LCD were experimented. Problems like colour shift, low contrast, large area of LCD chips hampered its candidacy for digital cinema [1].  In the LCoS a very thin layer of liquid crystal impressed with a voltage that is proportional to the pixel value. Depending upon the voltage the incoming light is polarized. Thus LCoS acts as a ‘window blinds'. Depending upon the polarization either light will be reflected fully or absorbed. If light is reflected fully then white colour is seen by the patrons. Backside of the LCoS contains the necessary circuits and it is opaque. Thus LCoS can only reflect light. LCoS is a perfect analog system as its polarization capability is directly to proportional to applied voltage. Electro-optical characteristics of liquid crystal used to vary across devices. Most importantly it is susceptible to temperature variations [5]. 

        JVC has developed Direct Drive Image Light Amplifier (D-ILA) and Sony has developed Silicon Xtal Reflective Device (SXRD). Both these are primarily LCoS based systems only. In [5] it is reported that SXRD based projector uses 4.2 kW lamp but DLP based Christie uses only 3.3 kW lamp to produce same amount of lumens. 

3.  GLV light modulator

It is developed by Silicon Light Machines/Cypress Semiconductors. Stanford University has played significant role in its development. It is made up of ribbons that are placed adjacent to each other and their ends are attached to device. Below them there is a substrate of transistors. With the use of transistors, ribbons can be flexed by fraction of wavelength. Thus a diffraction pattern is created. A 2K GLV will have only 1080 ribbons. Entire length of each ribbon has to be divided (virtually) into 2048 locations and each location should be scanned by laser. This will produce 2048 x 1080 pixels.

Note

• lakh is a Indian unit to represent 100 thousand
• Reference material’s bias is not eliminated.
• Presented information may not be up to date.

 Source

1. “Digital Cinema: The Revolution in Cinematography, Postproduction and Distribution”, by Brian McKernan, McGraw Hill, 2005.
2. Digital Cinema, Xilinx Corporation (PDF, 1537 KB, https://www.student.cs.uwaterloo.ca/~cs781/digital_cinema.pdf). 
3. “Understanding Digital Cinema: A professional Handbook”, Edited by Charles S. Swartz, Focal Press, 2005, ISBN: 0-240-80617-4.
4. G.P. Pinho, Optics of Digital Cinema, Christie Digital Systems. (PDF, 195 KB, https://www.student.cs.uwaterloo.ca/~cs781/PinhoDigitalCinemaTalk.pdf ).
5. Alen Koebel, A white paper on Digital Cinema projection, choosing the right technology, Christie Corporation. (PDF, 2641 KB).

Digital Cinema – Film vs. Digital Print

       We all know that movies are very powerful in terms of financial strength and the impact it has on the society. This multi-billion dollar industry started blossoming in 19th century. If ‘talking cinema’ (i.e. visual with audio) is taken as birth of cinema then it was in the year 1927. The name of the movie is  The Jazz Singer [1]. Nearly for a century movies were shot on film and it was developed with photo-chemical process. Projectors were used to rotate the film reels in a constant speed in front of a powerful lamp. The images created were projected on to a silver screen. People sitting on the dark enclosure were amused with the pictures shown. At the end of 20th century speech, audio, image and video were digitized. Slowly the ‘digital wave’ started engulfing the film technology. In this post, we will have a comparison between film and digital content.

The stakeholders of film are Actors, Technicians, Producer, Distributors, Exhibitors (Theatre) and Audience. One has to know the way movies are produced and role of each stakeholder in movie making process to understand the necessity for digital migration. Director of the movie makes the film on behalf of the Producer. So the right of movie lies with producer or Production Company. Region wise distributors are selected based on bidding and right to screen awarded to them for few weeks. Distributors in turn make contract with exhibitors to release the film in their region.

Movie making is made up of three stages: Pre-production, Shooting and Post production. Pre-production stage deals with story selection, screenplay and actor selection and signing contract with them [4]. Shooting is where movie scenes are shot with actors in various locations. It is a very time consuming process. A scene that lasts for minute in movie, Indian directors spends at least a day. Post production is much more time consuming process. Here raw footage that is shot in various locations is processed and arranged into a feature film.

Every day after shooting today’s footage is readied in the Lab for filmmakers to view. This is called dailies and in outside US it is called ‘rushes’. This acts as a feedback for director and camera man. In the Lab, raw footage is made into negative. Then they perform colour correction on negative but it is called as timing. Negatives are rearranged and if required cropped by director with the help of editor. This process is called as editing. Most of the time visual effects (VFX) scenes are added to make the movie worth watching. Actors jumping from 10th floor and other heroic stunts are possible due to VFX only. Then sound is processed and converted into optical signals and stored in twp sides of the film. Cropped and selected negatives are called ‘Cut Negative’. From the cut negative, ‘Answer Print’ is produced. Around 3000 release prints are developed from answer prints for world wide release. Regional movies will have at maximum 400 prints [4].

Star Wars Episode II : Attack on the Clones was the first
 movie fully shot  on  digital camera.  It was in the  year 2002.

Pros of Digital print

• Cost of 35mm film print is around €1,500 but the cost digital print that is stored in computer hard disk is only €150 [3]. The cost reduction is substantial when the number of release prints is high.  This forces producer and distributor to embrace digital print.
• Unlike film, making a new copy of digital release print is easy and economical. This feature makes piracy market to thrive well. To combat this encryption techniques are extensively used.
• After several screening, film prints gets into wear and tear. In old film prints lot of scratches will be visible and it will annoy the viewers. This will not occur in digital print.
• Proliferation of TV and DVD on homes started reducing movie goers. To retain the flock directors were forced to make visually stunning shots. When these shots are seen on a standard definition television (simply old CRT TV) they are not impressive. This forces audience to throng movie halls. Nowadays lot of Computer Generated Imagery (CGI) used in VFX. The best example is Steven Spielberg’s Jurassic Park. By nature CGI is digital.
• Proliferation of Non linear editing. Earlier days at the time of editing negatives physically cut and spliced together.  In TV production they use few video players that are loaded with same raw footage. The first cut will be played from one player and second cut from another player and so on.  To change a cut one has to just change video players start and stop time. This helped making changes easy and after finalization cuts were copied into new video cassette.  As the process is non-destructive, original negative is preserved well. Slowly this technique was adopted by movie industry. If the negative is in digital form then it will much easier to perform on a computer.
• Post production process time can be reduced considerably if film makers work on digital format. The level flexibility digital offers are really high. 

Pros of film print

• Film is a proven and mature medium. 
• Film equipment availability is not an issue and they are economical.  
• 35 mm film is accepted as a movie standard worldwide. We have 16 mm, 8 mm formats also.
• Even today, a century old 35 mm film stock can be projected on a silver screen any where in the world with the existing projectors. This is amazing when we consider the fact that two decade old software files are nearly unreadable. Thus the information is lost altogether.  
• Huge amount of film stock is available as archives. So equipment's like projectors should be made available to protect and preserve the archives. Conversion of film archive into digital format and indexing the digital prints is tedious and capital intensive.
• Raw footages are scanned and made into digital format called  Digital Intermediate (DI). All the post production process is carried out on DI and at last release print is made in film. This technique combines the benefits of digital format and robustness of film. 
• Film projectors are cheap compared to digital projectors. If there is malfunctioning of film projector then either projector operator or local mechanic are capable to rectify them.  In digital projector company service technician has to arrive and rectify the malfunction.
• 35 mm has more dynamic range, colour gamut compared to digital print. Analog projectors can project colour films with density range 5.0 which is equivalent to 17 stops [5]. Digital projector yet to arrive to match this feat.
• Film does not have the problem of defective sensor or thermal noise problem. This problem in digital media arises because of underlying technology (CMOS or CCD) they employ.

All the points supporting film is taken from [1].  One will conclude the fight between film and digital is really tough. But the day will come when digital print reign supreme.

References 

1. Brian McKernan, Digital Cinema, The revolution in Cinematography, post production and distribution, McGraw Hill, 2005.
2. Charles S. Swartz (Editor), Understanding Digital Cinema : A Professional Handbook, Focal Press, 2004. (ISBN: 978-02408-06174) 
3. Digital Cinema in Ireland, A review of possibilities, http://www.irishfilmboard.ie/files/reports/Digital_Cinema_in_Ireland.pdf, (PDF, 1510 KB)
4. Private discussion with an VFX expert working in Prism & Pixels VFX Studio, http://www.prismnpixels.com
5. Archives and digital cinema, http://ec.europa.eu/avpolicy/docs/reg/cinema/june09/archives_dcine.pdf (PDF, 361 KB).

Three Musketeers - Appendix

Earlier post dwelt on aperture, ISO and shutter speed. After posting it, I got following website.

http://www.markraymondmason.com/tips35a.php

Figure 1. Various aperture size

I failed in earlier post, to put a picture like above. I hope figure 1, makes easier to visualize aperture size. I have searched lot of webpages regarding shutter speed, ISO and aperture size. All the webpages give theory and at  maximum they may provide few images. But in this website they allow the user to interact with the images and get a FEEL about  shutter speed.  In figure 2 they provide three options Slow, Medium and Fast. User can select any one and find the corresponding result. Lot of examples like this. Please visit.

Figure 2.  Shutter speed with three options. Here Slow and Fast option is selected