Use lots of Light
The most common reason for poor quality images is a lack of light. Generally, the more light, the better the image. With too little light the image will become blurred and dull in colour. Lux is the standard unit for the measurement of light.
At least 200 Lux is required to capture a good quality image. A high-quality camera might be specified to work down to 1 Lux. This means that you can capture an image at 1 Lux; not that you will obtain a good image at 1 Lux.
Avoid Back Light
Try to avoid bright areas in images. Bright images become over exposed (bright white) and objects can then appear too dark. The problem typically occurs when attempting to capture an image in front of a window.
Reduce the Contrast
A camera adjusts the exposure to obtain an average level of light in the image. When trying to capture an image of an object in front of a white wall, the object tends to appear too dark. Substituting a grey background instead of a white background may solve this problem.
Light Levels in Typical Environments
The range of lighting from bright sunlight to clear starlight is 109:1 (100,000,000):1. To accommodate this range cameras are fitted with an automatic iris. Bright sunlight (100,000 lux), overcast day (1,000 lux), twilight (10 lux), street lighting (5 lux), full moon (0.1 lux). For a reference guide to "Choosing the right lens", please refer to .
Light Levels in Typical Environments
Environment
Type
Light level in Lux
Manufacturing Assembly
Rough
200
Medium
500
Fine
1000
Banks
Lobby
200
Offices and Cages
500
General Buildings
Dinning Rooms
100
Halls and Corridors
150
Outdoor Entrance
30
Hospitals
General Surgery
500
Operating Table
18000
Examination Table
500
Manufacturing Inspection
Rough
200
Medium
500
Fine
1000
Offices
General
500
Accounts
750
Hotels
Bars
150
Restaurants
100
Kitchens
500
Parking Areas
Outdoor Night
10
Garage
50
Retail Stores
Small
200
Large
500
Warehousing
Good Lighting
100
Poor Lighting
50
Typical
10
Reflectance
A camera sees only the light reflected back to it from the subject in the scene. Only an optically perfect mirror would reflect back 100% of the light shone on it. Anything else is comparatively poor at reflecting light. When light strikes a scene or object some is absorbed, some is diffused in scattered directions and some is reflected back to the camera. The amount of light reflected back to the camera is defined as a percentage of the light illuminating the subject. This is the reflectance of the scene. Some typical values are given below:
Typical Refectance Values
Scene
Reflectance
Matt white test card
89%
Snowy scene
85%
Glass windows and walls
70%
White matt paint on concrete
60%
Unpainted concrete, car park
40%
Red bricks
35%
Open country, trees, grass
20%
Empty asphalt area
5%
The Type of Image Sensor
There are two types of : CCD (Charged Coupled Device) and CMOS (Complementary metal oxide semiconductor). CCD sensors are produced using a technology developed specifically for the camera industry, while CMOS sensors are produced by the same technology used for the chips used in computers. High quality cameras invariably use CCD sensors. Although recent advances in CMOS sensors are closing the gap, they are still not suitable for cameras where the highest possible image quality is required.
The Ability to Correctly Capture Moving Objects
In addition to good light sensitivity, another key feature of digital image capture is progressive scan technology. The use of progressive scan means that images do not suffer from the "saw" effect that hampers interlaced video technologies used in telivision and traditional analogue CCTV cameras, in order to enhance the image frequency in moving images. Please refer to for more information.
File Size and Bandwidth Requirements
Digital cameras use image compression. To achieve a high frame rate image compression should be performed by hardware. There is a trade off between high quality images and compressed images that require much less bandwidth. The JPEG standard is used to achieve the highest possible quality, and MPEG is optimised for lower bandwidth requirements. For a reference guide to "Image Compression ", please refer to .
