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Digital for Casino Operators

For WorldGameProtection prepared by Vlado Damjanovski

B.E.(electronics)

www.cctvlabs.com

www.cctvseminars.com

http://www.cctvfocus.com

Why Digital?

Digital signals are virtually immune to noise.

Digital signals can be reproduced many times with the exact same quality as the first time.

Digital signals can be easily authenticated.

Digital signals can be easily enhanced, processed and transmitted over various networks (LAN, WAN,…).

With the same hardware and only software changes products can be improved and new functions introduced.

Analogue/Digital

ADC

Compression Types

Image Compressions (JPEG, Wavelet, JPEG-2000,...) Used in Multiplexing DVRs Measured in kB per image (typical from 10kB~100kB) Advantage: Single image self-sufficient; Various cameras can be mixed in the same footage Disadvantage: Needs more hard disk space; Cannot playback interlaced analogue video @ 50 fields/second Video Compressions (MPEG1, MPEG2, MPEG4, H.264,...) Used in single Streaming DVRs Measured in Mb/s (typical from 1Mb/s ~ 8Mb/s) Advantage: More hard disk efficient compared to Image compression; Better image quality when continuous playing back; Interlaced playback possible Disadvantage: Needs continuous streaming from the same camera signal for efficient compression. Sudden changes (PTZ movement) introduce artefacts Prepared by Vlado Damjanovski CCTV Labs Pty.Ltd. © 2007 www.cctvlabs.com

The Compression compromise

The digitised and compressed image can never be better than the original camera signal. But it can appear the same to the naked eye if a good compression is used.

The trick is to find the best compromise of high compression without loosing perceptible quality.

In Broadcast TV this has been achieved by using MPEG-2 at 4~8Mb/s, e.g. 4 is used for DVDs and 6 for cable TV.

In CCTV MPEG-4 is also used, where 2~3 Mb/s should give similar results.

The Camera importance

There are many important camera specification, but not all of them affect the end picture quality equally (after digitising and compressing).

Noise and low dynamic range for example may produce more artefacts than wanted. This in turn makes cards and chips hard to see. Noisy signal also produce larger file size/streaming.

Resolution is important, but the ITU-601 standard has a limit of 450 TVL, hence no effect of much higher resolution.

If there are no details in the original camera video signal no DVR or image processing device can “invent” them. The end result can only be as good as the input.

Key Camera Qualities

Some of the more important camera qualities: Resolution (in “TVL”) Depends on the chip, but also on the TV standard (PAL/NTSC) Typical SDTV = 480TVL, after ADC = 450TVL Dynamic range of the image chip (pure number ratio or in “dB”) for example CCD (50~80dB) vs. CMOS based like Pixim (120dB) Signal/Noise ratio (in “dB”) >48dB Colour reproduction (colour fidelity) AWB / ATW - light source, visual comparison, vectorscope Low light performance e.g. 1 lux @ F1.4 / 1Vpp vs. 0.1 lux @ F1.0 / 300mV Prepared by Vlado Damjanovski CCTV Labs Pty.Ltd. © 2007 www.cctvlabs.com

The SDTV Resolution

Typical Standard Definition CCTV camera has 480 TVL.

When using the ITU-601 ADC standard this produces 720 x 576 pixels for PAL, with a camera equivalent resolution of 450 TVL.

The most important thing would be to get the camera to produce the best image you can.

Compressed image can never be better than the original uncompressed image.

Image details

Defined by pixels (after the ADC) CIF (Common Interchange Format) 352x288 introduced with video conferencing and MPEG1 in the 1980-es. Equivalent to VHS quality.

The maximum number of pixels when using SDTV converted to digital at full TV frame (4CIF) is 720x576 pixels in PAL = 414,000 pixels and 720x480 in NTSC = 345,000. Equivalent to DVD quality.

When using 2CIF (equivalent to a TV field) the resolution is 720x288 when captured, but this is also converted to 720x576 when displaying, by duplicating each line (hence the jagged edges effect). When reproducing images in TV frame mode (4CIF) the “interlace effect” needs to be considered when displaying on computer monitors. Prepared by Vlado Damjanovski CCTV Labs Pty.Ltd. © 2007 www.cctvlabs.com

CIF / 2 CIF / 4CIF

How many Pixels are sufficient?

It depends what you are looking at (people, vehicles, cards,...) It is defined by the camera angle of viewing and distance.

Image size in pixels. Also, the compression plays a significant role.

For example, how many elements can you guess in the following pictures?...

Image = 32x24 pixels (card = 12 pixels height)

Image = 64x48 pixels (card = 24 pixels height)

Image = 128x96 pixels (card = 48 pixels height)

Image = 256x192 pixels (card = 96 pixels height)

Image = 512x384 pixels (card = 192 pixels height)

Compression factor

Dynamic Range

Definition: Ratio between the maximum number of electrons in a pixel created by a very bright scene and the lowest number electrons above the noise level.

Human eye has a DR of 120dB (100,000 : 0.1 lux).

CCD chips, by design, have a DR of 50~80dB (between 5,000~10,000 : 1).

Some camera manufacturers use double exposure with their CCD chips to achieve apparent Wide Dynamic Range (WDR).

Smaller chips (1/4” vs 1/3”, or 1/3” vs 1/2”) by definition have smaller DR.

The new pixel controlled CMOS chip (like Pixim) can achieve 120dB by applying variable electronic exposure for each pixel, depending on the light intensity.

DR Example

card = 48 pixels & high compression & low DR card = 48 pixels & high compression

Example

QuickTime™ and a DV decompressor are needed to see this picture.

CCD Samples courtesy of Pixim Inc.

Pixim CMOS

Average vs Pixel Luminance Metering

Don’t Forget The Lens

Many take lenses for granted, but not all lenses are equal If a lens is of lower optical quality even the best camera will produce inferior images Key lens qualities: Focal length (mm) Resolution (lp/mm) Light gathering ability (F/stop) Optical quality (glass, plastic,...) Mechanical quality (lens movement, focus, zoom,...) Electronic quality (Auto Iris, Focus, Level, ALC,...) Distortions (barrel, pincushion, colour,...) Prepared by Vlado Damjanovski CCTV Labs Pty.Ltd. © 2007 www.cctvlabs.com

Other Factors that influence The Quality

Light contrast of the scene (white cards vs. table cloth).

Illumination angles relative to camera position (avoid direct reflection).

Camera AGC (High AGC not always good, sometimes manual may be better).

Lens iris setting (Manual vs Auto iris).

Temperature (higher temperature = higher noise => lower DR).

DVR compression gamma (type and level).

Monitors

Once camera video signal has been captured, digitised, compressed and stored (recorded), it then has to be decoded and displayed on a monitor.

Monitors convert digital signal back to analogue. Human eyes (like ears) can only detect (see/hear) analogue signals.

Monitor display quality influences the overall video signal quality. Monitors should have at least the same resolution as the cameras.

Contrast, brightness and gamma setting - also important.

Even with the best camera, most accurate lighting selection, good choice of video compression and recording system - if the display is inferior, the final result will be inferior.

Optimal Viewing Distance

In addition to all previously mentioned, an important factor in image quality is the environmental conditions (control room light conditions), but also the Optimal Viewing Distance.

CRT vs LCD & Plasma

CRT (Cathode Ray Tube) are monitors specifically designed for analogue “live” video using the Interlaced effect (PAL and NTSC).

LCD (Liquid Crystal Display) are monitors specifically designed for the computer industry and they do not use interlaced scanning.

Analogue video looks better on CRT, as it is designed for it.

Computer display looks better on LCD, as it is designed for it.

Displaying Analogue video on LCD is possible, but the image quality is reduced as it needs to be converted.

Plasma has mixed properties of CRT and LCD, but it is usually designed with 16:9 aspect ratio for HDTV, not 4:3, hence not ideal for SDTV.

LCD, Plasma and DLP are ideal for the new HDTV, not yet used in CCTV.

Conclusion “In the digital word of CCTV - A picture is worth more than a thousand pixels” 400,000 to be more exact, but the story being told by these words can easily be lost if we don’t take care of every single pixel.

Thank You

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