In my earlier posts I have already explained the working of Charge-coupled devices and its application as an image sensor. Recently, most of the scanners and cameras have introduced a new image sensor called Contact Image Sensors [CIS]. To know more about CCD and its applications click on the links below.

TAKE A LOOK : CHARGE COUPLED DEVICES (CCD)

TAKE A LOOK : WORKING OF DIGITAL CAMERAS

TAKE A LOOK : WORKING OF SCANNER

Working of Contact Image Sensor

Contact Image Sensor is one compact module consisting of three sub-systems. They are

1. Illumination system

The illumination system consists of two sets of LED’s which is used to illuminate the document that is to be scanned. Each LED pack consists of LED’s of the three composite colours – Red, Green and Blue. These three colours join together to form the white light. The light from the LED is focussed with the help of light guides. The way the LED glow depends on the type of scan that is required. If a colour scan is needed all the LED’s will glow at high intensities. If a black and white scan is enough, the LED’s will shine simultaneously.

The main advantage of LED in CIS when compared to fluorescent bulbs in CCD is that they glow at a constant rate the minute they are turned on. But, fluorescent bulbs need a warm-up time as they begin to glow. They also have the advantage of being turned off whenever the device is not in use. Thus they help in saving a lot of power and are also environment friendly.

2. Optical system

The optical system consists of an array of lenses and a focus that is used to carry the light reflected from the document to be scanned to the light sensing system. Unlike a CCD, the optical system in CIS is shorter and less complex. This helps in saving more space and is also economical. As the apparatus is lighter and compact, it is applicable in making portable scanners.

3. Light sensing system

The light sensing system mainly consists of a sensor with a silicon surface. The light intensity that hits on the silicon surface varies according to the document to be scanned. The silicon surface will be divided into square cells. Though the same mechanism is carried out in a CCD, there is a difference in the ratio of the cell size to the information size. Here, the size of the information hitting on the silicon cell is same as the size of the cell. That is, for a 500 dpi scanner each cell will be 1/500″ across. Thus the ratio is 1:1. Thus, the need for the reduction or enlargement is no required in such a device. For this reason, the sensor will be kept very near to the document to be scanned. Most sensors rest right under the document at a distance of about 13 millimetres. As soon as the light hits the sensor, this will be recorded and will be converted into an electrical signal.

Take a look at the picture below to get a clear understanding.

Contact Image Sensors (CIS)

Advantages of Contact Image Sensor (CCD vs CIS)

• The size of contact image sensors is very small and also lighter than the CCD sensors. They are always available as contact image sensor modules. That is, all its associated optical devices are included in a single compact module. This will also help in producing very flat and light-weight scanners. They also pave the way to applications in cameras and so on.
• These Contact image sensor scanners do not consume as much power as CCD scanners. They are also equipped to run with in battery power and can also be connected through USB port.
• When compared to a CCD, the sharpness of the image that is scanned is more for a contact image sensor. Thus they are applicable for scanning documents which requires even the smallest details to be displayed.

Disadvantages of Contact Image Sensor (CCD vs CIS)

• The image quality of a CIS is much lower when compared to a CCD sensor. The quality of the picture and the picture resolution is poor in comparison.
• As the depth of the field is limited to a certain extent, there will be problems while scanning a material that is nor completely flat in nature.
• In large scanning formats, CCD sensors use white LED’s or white fluorescent tubes for the colorization. In color compact image sensor, this is replaced by the composite color composite LED’s. The CIS LED’s cannot provide a wide range of color as CCD can. Thus CIS is not suitable for large scanning formats of photos or colourful documents with shadow details.

Applications of Contact Image Sensors

• The largest application of the device is in the field of scanning. Contact Image Sensor scanners have taken a large part of the industry. Since the CIS is lighter and smaller in size than CCD arrays, they are used in scanners that can be carried around. The most commonly used Contact Image Sensor scanner is the flat-bed scanner. The most famous brand among these is the Canon contact image sensor.
• Other applications of Contact image scanners include bar-code readers, electrograph and also optical identification technology.

What is a Scanner?

A scanner is a device that is used for producing an exact digital image replica of a photo, text written in paper, or even an object. This digital image can be saved as a file to your computer and can be used to alter/enhance the image or apply it to the web. The most comonly used scanner is the flatbed scanner, in which you keep the object on top of the glass window. The scanned output will be obtained in your computer. The image and text are obtained exactly through the process of optical character recognition [OCR].

Scanner

The historical precedence of scanners originates from the telephotography input devices, which was mainly used by the printing press. It mainly consisted of a rotating drum, which rotated at a maximum speed of 240 rpm. The signal used was analog in nature and were sent through telephone lines to the receptor end. The receptor recognizes the signal synchronously and a proportional output is printed on special paper.

Types of Scanners

1. Drum Scanners

Drum scanner was the first ever image scanner to be developed. It was made in the year 1957 at the US National Bureau of Standards. The first image was black and white with a resolution of 176 pixels.

This scanner is mainly used in the publishing industry. The technology used behind the scanning is called a photomultiplier tube (PMT).

As the name implies, the drum scanner consists of a drum type cylinder on the top of which the image/document to be scanned is mounted. This cylinder rotates at a very high speed and thus the object placed on it will deliver the image copy with the help of precision optics. Though the precision optics sends the reflected light from the image, they will be sensed by a sensor in the PMT. It will be received by the filter in the PMT and the replica is made. Modern drum scanners can also recognize colour images by using three separate colour filters. Each colour filter will be for each composite colour [RGB]. The reflected light will be split into the three colours and will be filtered.

The size of the image produced depends on the design of the drum by the manufacturer.

This scanner finds its application in publishing field because of its ability to capture the smallest details out of film negatives. It also has an advantage in its ability to control sample area and aperture size independently. This feature helps in clearing the grains in negative films as well as colour films while scanning it.  Thus, they also help in producing scans that are high in resolution, colour gradation and value structure. As the resolution may be increased up to 12,000 PPI, they are particularly useful when a scanned image is to be enlarged.

After the invention of flatbed scanners, the production of drum scanners has been limited. A flatbed scanner also has the same features, but at a lower production cost. Still drum scanners are used in places like printing of high quality books and magazines and many other publishing areas.

2. Flatbed scanners

Flatbed scanner is the most commonly used scanning machine nowadays. They are also called desktop scanners. The detailed working of flatbed scanners will be given below. They use Charge-coupled device (CCD) to scan the object. To know more about CCD click on the link below.

TAKE A LOOK : CHARGE-COUPLED DEVICE (CCD)

3. Hand-Held Scanners

This device found popularity during the early 90’s. Hand-held scanners are used to scan documents by dragging the scanner across the surface of the document. They are available as document scanners as well as 3-D scanners. This scanning will be effective only if with a steady hand technique, or else the image may seem distorted.  They have sensors to detect the distortion rate and an indicator will be provided to alert if the motion of the scanner is too fast.

They also have a START button, which has to be on during the scan duration. They are synchronized with the computer and also have an automatic optical resolution. The scanner also has LED’s which light up the image to be scanned. As the image can be distorted most of the time there are special reference markers available in the device which helps in compensating the distortion.

Though poor image quality is obtained, fast scanning of texts can be done with this device.

4. Film Scanners

This device is manufactured to specially scan positive and negative photographic images. The film will be inserted into the carrier. It will be moved with a stepper motor and the scanning process will be done with a CCD sensor. The output can be obtained on a computer.

Working of Flatbed Scanner

The main difference in the old scanners and modern scanners is the type of image sensor used. In old scanners, a photomultiplier tube [PMT] was used. For modern scanners a Charge-coupled device [CCD] is used. A CCD sensor is used to capture the light from the scanner and then convert it into the proportional electrons. The charge developed will be more if the intensity of light that hits on the sensor is more. To know more about CCD click on the link below.

TAKE A LOOK : CHARGE-COUPLED DEVICE (CCD)

Any flatbed scanner will have the following devices.

• Charge-coupled device (CCD) array
• Scan head
• Stepper motor
• Lens
• Power supply
• Control circuitry
• Interface ports
• Mirrors
• Glass plate
• Lamp
• Filters
• Stabilizer bar
• Belt
• Cover

Though the configuration of the above components differs according to the manufacturers design the basic working is almost the same.

A scanner consists of a flat transparent glass bed under which the CCD sensors, lamp, lenses, filters and also mirrors are fixed. The document has to be placed on the glass bed. There will also be a cover to close the scanner. This cover may either be white or black in colour. This colour helps in providing uniformity in the background. This uniformity will help the scanner software to determine the size of the document to be scanned. If a page from a book is to be scanned, you may not be able to use the cover.

The lamp brightens up the text to be scanned. Most scanners use a cold cathode fluorescent lamp (CCFL).

A stepper motor under the scanner moves the scanner head from one end to the other. The movement will be slow and is controlled by a belt. The scanner head consists of the mirrors, lens, CCD sensors and also the filter. The scan head moves parallel to the glass bed and that too in a constant path. As deviation may occur in its motion, a stabilizer bar will be provided to compromise it. The scan head moves from one end of the machine to the other. When it has reached the other end the scanning of the document has been completed. For some scanners, a two way scan is used in which the scan head has to reach its original position to ensure a complete scan.

As the scan head moves under the glass bed, the light from the lamp hits the document and is reflected back with the help of mirrors angled to one another. According to the design of the device there may be either 2-way mirrors or 3-way mirrors. The mirrors will be angled in such a way that the reflected image will be hitting a smaller surface. In the end, the image will reach a lens which passes it through a filter and causes the image to be focussed on CCD sensors. The CCD sensors convert the light to electrical signals according to its intensity. Take a look at the diagram given below.

The electrical signals will be converted into image format inside a computer. This reception may also differ according to the variation in the lens and filter design. A method called three pass scanning is commonly used in which each movement of the scan head from one end to another uses each composite colour to be passed between the lens and the CCD sensors. After the three composite colours are scanned, the scanner software assembles the three filtered images into one single -colour image.

There is also a single pass scanning method in which the image captured by the lens will be split into three pieces. These pieces will pass through any of the colour composite filters. The output will then be given to the CCD sensors. Thus the single-colour image will be combined by the scanner.

In some recent scanners, a contact image sensor [CIS], has replaced the CCD sensor. Though this method is not as expensive as the CCD scanner, the quality of the image produced and the resolution is much lower. To know more about CIS, click on the link below.

TAKE A LOOK : CONTACT IMAGE SENSORS (CIS)

Parameters of a Scanner

• The resolution of the image is one of the main parameters of the scanner. Each scanner varies according to its resolution and hence the cost. The resolution may be expressed in pixels per inch [ppi] and also samples per inch (spi). But, instead of defining the scanner’s correct optical resolution the manufacturers mostly define the interpolated resolution of the scanner. The latest flatbed scanner has an interpolated resolution of 5400 ppi and almost 12,000 ppi for a drum scanner.
• Interpolated resolution actually refers to the increase in the resolution of the image with the help of the scanning software. This is done by adding extra pixels in between the ones actually scanned by the CCD array. These extra pixels can be added only as an average of the adjacent pixels. Suppose a scanner has a true resolution of 300×300 dpi and the interpolated resolution declared by the manufacturer is 600×300 dpi. Thus an additional pixel is added in each row of the CCD sensor by the software. As the resolution increases, the size of the file also increases. This size can be reduced through lossy compression technique like JPEG. Through this method the quality of the picture will only be reduced to a small amount. Usually this method is done to load an image faster on the internet and also to print the image on a full page.
• A scanner has a least original resolution of about 300×300 dots per inch (dpi). This increases with the increase in the CCD sensors row wise and also by the precision of the stepper motor.
• As the scanner’s lamp brightness increases along with the use of high quality optics the sharpness of the image also increases. Density range is another parameter through which the minor shadow and brightness details can also be reproduced through scanning. The higher the density range, the higher the details.
• Another parameter used is the colour depth. In colour scanning, the colour depth refers to the number of colours that can be reproduced by the scanner. Though a 24 bit/pixel scanner is sufficient enough there are scanners with 30 bits and 36 bits available now.

Scanner to Computer Connection

The image that has been successfully scanned has to be transferred to our home computer for useful applications.  For this transfer to occur, two main problems have to be dealt with. They are

1. Physical connection between the scanner and computer.

• Parallel Connection

This is one of the oldest method and the slowest method available. Though this type of connection is much economic it only had a data transfer rate of 70 kbps.

• Small Computer System Interface [SCSI] Connection

This method can be appropriate only with the help of an SCSI interface card. Earlier the scanners used to come with a dedicated SCSI card. Though the data transfer rate is high enough, much more economical and easier connections like the Firewire and USB came in its place.

• Universal Serial Bus [USB] Connection

USB connection is the latest and most economical method of data transfer. It has speeds up to 60 MBPS and can be easily connected to the scanner.

• FireWire Connection

This is the fastest of all the above methods. It has been introduced in the latest high-end scanners and is ideal for scanning high resolution images. It can transfer data at a maximum speed of 800 MBPS.

2. Transfer of information from the scanner to computer

For the transfer of information from the scanner to the computer application programming is the main solution. For this there are also Applications Programming Interfaces [API]. Through API standards a computer can transfer the details with any scanner without even knowing the details of the scanner. The most commonly used software for transferring details from the scanner is the ADOBE PHOTOSHOP. Photoshop supports a standard called TWAIN. If the scanner also supports the same standard, then transfer of information can be done. The TWAIN API is used in most scanners and is also used in most high and low-end equipments. TWAIN is just like a driver which helps in communicating with all other scanners in a common language.

Processed Data

After reaching the computer, the actual output will be a non-compressed composite image. This image will be later edited in Photoshop or other graphics programs to convert it into lossy compresses JPEG format or non-lossy compressed PNG format. If it is a text image, it will be converted to .txt file with the help of Optical character recognition (OCR) software’s. The text will be accurate depending on the clarity of its image.

Automatic cleaning technique of a scanner

The films used in scanning may be prone to dust and scratches. Modern scanners have an in-built cleaning process called infrared cleaning. In this method an infrared beam will be used to scan the film. When the beam hits places with dust and scratches, the beam will be cut-off. Thus the correct position, size and also the shape of the dust will be calculated and will be removed. Most modern companies like Nikon, Microtek and Epson name this technique as Digital ICE while Canon calls this technique as Film Automatic Retouching and Enhancement system [FARE].

Applications of Scanner

1. Applications vary according to the type of scanner used. Flatbed scanners are mostly used for scanning documents. But, for large format documents a mechanical scanner will have to be used.
2. There are hand-held scanners which are used for scanning an object according to the movement of our hand [the scanner does not move by itself]. This scanner helps in 3-D scanning of materials and is applicable in industrial designs, test and measurement of devices, gaming applications and so on. 3-D scanning can also be done with the help of planetary scanners. There are also developments going on in producing a combination of 3-D scanners with digital cameras so that realistic photos with true colour can be obtained in the 3-D mode.
3. A new concept called reprographic cameras has paved their way for digital camera scanners. This type of scanner has many advantages like easy digitalization of large format documents, high processing speed, and portability and so on. They also produce high resolution images with anti-shake features. Studies are still going on to remove the main disadvantages like shadow and reflection interference, image distortion and low contrast.
4. Scanners also find high end application in field like bio-medical research. High resolution scanners with a resolution of almost 1 µm/ pixel are used to detect DNA microarrays. Here also, the charge coupled devices are used for detection.

An article regarding the detailed working of a DVD has been explained earlier. To know more about it, click on the link below.

TAKE A LOOK : WORKING OF DIGITAL VERSATILE DISC (DVD)

Now we are going to look at how a DVD player works and the essential components for its working.

Parts of a DVD Player

The DVD player is not only used for playing the data present in a DVD, but also to write the content onto a DVD. To know this process it is essential to know the basics of a DVD.

As told earlier, DVD’s have pits and bumps in their track which holds the information that is required to be played. This information can be a video, audio or a mixture of both. When a DVD player reads this data, the smooth surface is usually taken as a ‘0′ and pits are usually taken as a ‘1′.

In order to create as well as read these data, a red laser with a wavelength of 600 nanometers. This is about 180 nanometers lesser than the wavelength of CD, which enables it to have a higher density of pits. Thus the size of the DVD increases. Though the first released DVD’s were only a single layer, 2 layered discs have been released nowadays. Single layer can hold only up to 4.7 GB of data while double layered DVD can hold up to 17 GB of data. The DVD design is similar to a CD a reflective silver layer in the centre and a semi-transparent gold layer on the top of it.

A DVD does not have the capacity to hold hi-def movies. So a MPEG-2 compression system is introduced. As this is used, the data will be encoded onto the DVD as elements of the changing frames. This has to be successfully decoded and decompressed by the DVD player.

Thus the parts of a DVD player are

1. Disc drive mechanism

The disc drive mechanism consists of a motor that will drive the disc in a circular motion. The mechanism will also have a disc feed – a loading tray that is used to accept the DVD from the user. Thus the entire disc drive is basically a spindle that holds the disc and a motor that is used to circle the disc. The spindle is held in its position with the help of small gears and belts that are attached internally. Some players have an automatic feed system in which, there will be no tray. Instead the disc will be automatically recognized after inserting a part of it.

2. Optical system

The optical system mainly consists of the laser beam, lenses, prism, photo-detectors and also mirrors. The output of this mechanism will be the input for the disc-drive. The laser beam will be a red laser diode which works at a wavelength of 600 nanometers. The optical system also requires a motor to drive it. The laser system and photo-detector is placed together on a single platform. The laser diode as well as other diodes is made with the help of glass.

3. Printed Circuit Board

The PCB is similar to that of any other electronic circuits. The electronic outline must be drawn on the PCB with the correct placement of all the IC’s resistors as well as capacitors. After the outline has been drawn, the components must be soldered to their respective places. All this must be done in a very clean environment so that the board does not become contaminated by dust. All the primary components of the electronic circuit should be made out of silicon.

Working of DVD Player

Take a look at the basic block diagram of how a DVD player works.

Block Diagram of DVD Player

DVD Player-Block Diagram

The pits and bumps in the DVD are hit by the laser from the optical mechanism of the DVD player. This laser will be reflected differently according to the change of pits and bumps. Though the laser hits a single spot, the DVD moves in a circular motion so that the entire area is covered. Mirrors are also used to change the spot.

These reflected laser beams are then collected by a light sensor (eg. photo-detector) which converts the different signals into a binary code. In short, the optical system helps in converting the data from the DVD into a digital code.

The binary signal is then sent to a Digital to Analog converter which will be setup in the PCB. Thus the corresponding analog signal of the DVD is obtained. The PCB also has amplifiers which amplify the signal and then sends it to the graphic and audio systems of the computer/TV. Thus, the corresponding audio/video signal is obtained. The basic working of a DVD player is shown below.

Assembling a DVD Player

As the different parts of the DVD player are all complicated electronic circuits, they are all manufactured by different people. They are later brought together and assembled at one place. During the assembling, the PCB will be connected to the rest of the machine and all the components are placed in the right positions. The whole package is then placed inside an outer plastic housing with a front panel with the buttons for various operations. This DVD player is then sent to a packaging station where they are placed safely inside boxes along with the respective power cords, operating manual, installing disks and so on. They are then taken by the distributors to various shops and then sold to customers.

Cautions while assembling a DVD Player

A DVD player will only be satisfactory to a customer only if it has a high performance. The degree of quality varies according to the flaws in the assembling process. Thorough inspections in both the visual as well as electrical divisions must be done most of the time. Flaws in the positioning of the different components can also cause the player to become faulty. After manufacturing the DVD also, the working performance is tested. To see the adverse effects of these players in different temperatures, the tests will be carried out in excessive heat as well as humidity. Since most of the parts of a DVD player is made by suppliers, they rely on other companies for good quality. The DVD assemblers will set a minimum standard for the supplies that they buy from outside. This specification must be met by them. The lenses and mirrors should be highly polished and cleaned before placing them.

After the invention of the Digital Versatile Disc [DVD], the true digital sound effect and high clarity video effects were brought to all homes.  But the hunger for high-definition videos and audio along with a high-capacity storage disc led to the invention of the Blu-ray Disc [BD]. They have the same capabilities of a DVD, storing audio, video as well as photos.

TAKE A LOOK : WORKING OF DIGITAL VERSATILE DISC (DVD)

TAKE A LOOK : WORKING OF FLEXPLAY DVD

Blue-ray disc

Blu-ray Disc – Definition

A Blu-ray Disc is a high density optical disc storage medium, which is used for the storage of all high-definition digital formats like audio, video, and play-station games and so on. They have the same physical appearance as a DVD. The name “BLU-RAY” is actually a combination of the colour “blue” and “ray”. Here blue refers to the blue colour of the laser that is used for its reading and ray refers to the optical ray. While trade marking a product, you are not supposed to include a common or everyday used word. Thus the letter ‘e’ from the word “blue” was omitted.

Blu-Ray Disc Specifications

1. BD is present in both single layer and double layer. The single layer Blu-Ray Disc has a capacity of up to 25 GB and double layer has a capacity of 50 GB. Though this is a practical storage capacity meant for the present Blu-Ray players, there are BD’s that have capacities up to 200 GB. These discs, though not marketed yet, can be played in any Blu-Ray player without any additional equipment.
2. Blu-Ray Disc needs a wavelength of 400 nanometer violet-blue laser for its reading at different speeds like 4.5 MBPS, 9 MBPS, 18 MBPS, 27 MBPS, 36 MBPS and 54 MBPS.
3. Blu-Ray disc can run formats that are encoded in MPEG-4 and MPEG-2.
4. BD is used for data storage, playing 1080p HD video and audio, 3-D Stereophonic and so on.

Blu-Ray Technology – History

There have been many questions on who invented the Blu-Ray technology. But this can be explained only by explaining the history of Blu-Ray technology.

Even though the High Definition TV was invented, there was no particular storage format, recorder or player for it. Thus companies like Toshiba started experiments on making a bigger size DVD. Lately, they released their own Blu-Ray player. During this war for HD technology, researches proved that short wavelengths (shorter than that of a DVD Blu-ray Disc) were enough to make discs with higher storage capacities along with optical capabilities. It was at this time that a researcher, Shuji Nakamura invented the violet-blue laser diode which was apt for a Blu-Ray Disc.

This invention was first applied by Sony Company. They were able to create Ultra Density Optical and also DVR Blue along with the help of Pioneer. These were considered to be the first replicas of Blu-Ray Disc. This was later exhibited to the world at February 2002 and an association was formed. It consisted of nine members, who were considered to be the inventors of Blu-Ray disc. The association was called the Blu-ray Disc Association. This association has now expanded with more than 5000 members all over the world. This association consists of many makers of electronic goods, computer hardware’s and also motion pictures.

Blu-Ray Disc (BD) vs DVD

• Both of them have the same physical appearence. [Thickness = 1.2 mm]
• The single layer Blu-ray disc can store up to 27 GB data. A singe layer DVD can hold only 4.7 Gb of data. Thus a BD can hold almost 13 hours of normal video and 2 hours of high-definition video. A double layer BD gas a storage capacity of 50 GB which can play almost 20 hours of normal video and 5 hours of HD.
• A DVD needs two substrates and they should be bonded. But a Blu-ray disc requires only one substrate.
• The production cost of Blu-ray is lesser than that of a DVD because there is no need for bonding of substrates. Thus the production materials are lessened. This causes a lesser production time than that for a DVD.
• The Blu-Ray disc uses violet-blu laser with improved lens specifications, while a DVD uses red laser. This causes the focus to increase, thus helping in the recording of both small and high density pits on the BD.
• The wavelength used for BD is 400 nanometers. DVD has a wavelength of 650 nanometers. This decrease in wavelenth helps in high density medium storage.
• The layer in a blu-Ray disc is very close to the laser lens on its player. Thus the precision of the data displayed will be higher with less distortion than a DVD.

Take a look at the comparison between DVD and BD from the figures below.

Types of Blu-Ray Disc

Similar to a DVD, BD also has different versions according to its application. The common types are

1. Read only memory Blu-Ray disc [BD-Rom] – This type of BD can only be read but cannot be written over. The content will be pre-recorded.
2. Recordable Blu-Ray disc [BD-R] – This BD is mainly used for storage of PC data.
3. Re-writable Blu-Ray disc [BD-RW] – This BD is mainly used for storage of PC data. The contents in this disc can be written over and over.
4. Re-writable Blu-Ray disc [BD-RE] – This BD is mainly used for recording of data to be used in HDTV. This disc can also be written over again and again.

Construction and Working of Blu-Ray Disc

Like a DVD, the BD also has pits and bumps. The only difference is that the pits and bumps are smaller and very closely packed. Blu-ray disc also has spiral tracks running from the centre to the edges of the disc. The information is stored in these tracks in the form of audio and video. These audio and video are introduced into the DVD after encoding it.

As told earlier a blue laser is used to focus on the DVD. The laser has a small wavelength of precisely 405 nanometers and must be highly accurate because the pits and bumps are smaller and packed closely. The information stored in the Blu-Ray disc is usually very small in size. They are only 0.15 x 10-6 meters long. Since all these are very small in size, a single-layer itself is more than enough to hold more than 25 GB of data. Thus if a double layer is used, they can easily hold information up to 5o GB.

The Blu-Ray disc does not have these issues because the data is stored on top of a poly-carbonate layer which is about 1 millimeter thick. This stops the problem of birefringence and causes no distortion to the reading of data. This also has an advantage in regard to the closeness of the data to the objective lens. Due to this closeness to the surface, the BD has a outside hard cover to prevent scratching and finger prints.

Because the data is closer to the surface, a hard coating is placed on the outside of the disc to protect it from scratches and fingerprints. The simple design helps in manufacturing these discs at a cheaper rate than a DVD. There is no need of moulding like a DVD.

Advantages of Blu-Ray Technology

• The sleek design helps in skipping from any part of the disc to the other
• Multiple programs like using the same disc for watching a video as well as recording on it  can be done at the same time.
• Watch HD in its maximum quality with very little loss.
• You can make your own playlists.
• The programs present on the disc can be re-ordered in any way you like.
• Use of subtitles is possible for movies.

To know more about Flexplay DVDs, you must also know the working of a normal DVD. Click at the link below to know more.

TAKE A LOOK : WORKING OF DIGITAL VERSATILE DISC (DVD)

What is Flexplay DVD?

In most foreign countries, people rent a lot of DVD’s from the shop. All you have to do is watch the movie and return the DVD back within the agreed time. But, if we are pretty much unorganized, we tend to forget about the DVD. This is where the DVD rental shop makes money. They take late fees and this money sums up to a large amount equal enough to buying a DVD. This disadvantage can be overcome by using a Flexplay DVD.

The Flexplay DVD, introduced by a company called Flexplay Technologies is a special type of DVD that can be rented and need not be returned back. The rental prices will be the same as that of a normal DVD. But this does not mean that you can keep watching the movie all your life. The Flexplay DVD has a fixed life, after which the DVD destroys itself. That is, there is an in-built stopwatch which starts automatically when you start playing the disc. The stopwatch is chemical in nature and is designed to destroy the DVD after a fixed time.

Advantages of Flexplay DVD

1. You are actually buying the Flexplay DVD for the same price as the rental DVD.
2. You need not return the DVD. So there is no tension on extra charges.
3. As there is no risk involved in selling it like a rental DVD, Flexplay DVD’s can be sold in any store.

How Flexplay DVD Works?

The working of a Flexplay DVD is very much the same as that of a Digital Versatile Disc [DVD], except for an additional component. Just like a DVD, the sound and video are digitally encoded into the Flexplay DVD. This information will be stored in the disc in the bumps and trenches in the DVD and thus form a long track of information. Like the normal DVD, Flexplay DVD will also have the tracks spiral in nature. These tracks will then be covered with the help of protective layers like poly-carbonate plastic and then a gold layer n top of it.

Like a normal DVD, this DVD also has two tracks with the same information holding capacity. They will also have two reflective layers out of which one is inside and the other is outside. The outside reflective layer will be semi-transparent. These two layers are stuck together with the help of resin adhesive, thus making a two-layer single disc.

DVD vs Flexplay DVD

The only difference between them is in an additional layer inside the disc. This layer is situated on the front side of the inside reflective layer. This layer is made up of a special transparent chemical compound that reacts with the external atmospheric oxygen to form another chemical compound.

The resultant chemical compound obtained is opaque in nature. When the laser beam of a DVD player passes through the different layers, the layers that are reflective causes it to read the DVD. But after the reaction, the opaque nature stops the DVD player from reading the disc. Thus the DVD shows the sign “No Disc”. The special layer cannot be easily setup inside the disc. For this, the manufacturers made a special adhesive that bonds the two separate layers with this layer.

In the beginning, when you purchase the Flexplay DVD, it is sold as an air-tight package. Thus, the DVD will not have any contact with the atmospheric oxygen. As soon as you open the package, the oxygen starts a slow reaction with the chemical. Though the reaction starts slowly, it later reacts quickly when it nears the expiry period. When the expiry period is near the special layer becomes opaque. This change can be understood easily by just looking at the disc. When the disc is take n out of the package it will have a red colour. After the complete reaction, the colour changes to black.

The expiry period of the disc is decided by the manufacturer and the chemical compound can be balanced accordingly.

Usually, there will be small chemical reactions even if the disc is kept in an air-tight package. But still the disc will be working properly for as long as one year, before it is opened. The special adhesive used in the bonding process helps in keeping the disc usable for a maximum of 48 hours without being damaged.

Though this technology has not yet been marketed, it will surely be a replacement for the rental DVD stores in future.

Disadvantages

Though the Flexplay discs can be economical to us, it  will not be so economical to the manufacturers. When each DVD is disposed off after watching, you will have to make many more copies for others as well. Though this may sound like profit, the selling of these DVD’s for cheap rental cash makes it a loss.

Recycling Options

The use and dispose of a large number of Flexplay DVD’s can cause serious environmental pollution. But the company has made tie-ups with many environmental organizations like Greendisk and Geo-tech polymers so that they can fully recycle the waste and thus maintain the environmental standards. All the wasted discs will be collected and the poly-carbonate plastic present in it will be recycled and later used for high-end applications. The company also claims that the pollution caused by the discs are not so harmful compared to the energy emitted due to the use of a vehicle to return the DVD back to the rental store.