Contrast ratio
Posted: Mon Jul 05, 2004 12:36 pm
This specification is used in marketing hype and promotion and is an unreliable figure for determining performance. Ignore it.
Contrast ratio simply put means how bright and how dark an image can be and is one element of understanding and defining dynamic range. Human contrast ratio is about 800 and anything beyond that may cause viewer fatigue. This is based on a dark room at night compared to being outside on a clear sunny day. For most of us just going outside of your house on a sunny day will make your eyes water and squint until your iris closes up to compensate. Of course once you step back in the house it will be too dark and it will take a few minutes for your iris to open back up. Imagine going immediately from a darkened closet to a sunny day outside; people would wonder if you are crying from the tears running down your face. You would not want that experience with a display or the image you are viewing.
The correct way to measure contrast ratio is to use a checker board pattern of 100IRE peak white squares and 0IRE peak black squares after contrast and brightness have been properly calibrated. In this way you are measuring how the bright parts of the image would degrade the dark parts of the image due to the technology of the display in a real world application. This is called intra-field contrast ratio and has real world value since it represents real dynamic range capability.
So what are the manufacturers doing to come up with outrageous contrast ratios? They set the contrast control for all the light output the display can create and set the brightness for the least amount of light output regardless of proper performance for an image. In other words they are taking the display out of correct performance using settings that no one would use because the image will not look right. On top of that they do not use the checkerboard pattern and instead use on / off contrast ratio using a 100IRE white raster and then a 0IRE black raster. Some go even further by turning the display off and measuring what ever light remains for black which in many cases is none. Using these methods they can come up with very impressive numbers in their literature but they mean nothing for your application.
It is quite possible to have a display with an extremely high on / off contrast ratio yet have a poor or typical intra-field contrast ratio. In such a scenario that means the display will be very bright but the image will be washed out lacking dynamic range.
A figure that tells us a little bit more and has some value is lumens found in the Video Dictionary.
Contrast ratio simply put means how bright and how dark an image can be and is one element of understanding and defining dynamic range. Human contrast ratio is about 800 and anything beyond that may cause viewer fatigue. This is based on a dark room at night compared to being outside on a clear sunny day. For most of us just going outside of your house on a sunny day will make your eyes water and squint until your iris closes up to compensate. Of course once you step back in the house it will be too dark and it will take a few minutes for your iris to open back up. Imagine going immediately from a darkened closet to a sunny day outside; people would wonder if you are crying from the tears running down your face. You would not want that experience with a display or the image you are viewing.
The correct way to measure contrast ratio is to use a checker board pattern of 100IRE peak white squares and 0IRE peak black squares after contrast and brightness have been properly calibrated. In this way you are measuring how the bright parts of the image would degrade the dark parts of the image due to the technology of the display in a real world application. This is called intra-field contrast ratio and has real world value since it represents real dynamic range capability.
So what are the manufacturers doing to come up with outrageous contrast ratios? They set the contrast control for all the light output the display can create and set the brightness for the least amount of light output regardless of proper performance for an image. In other words they are taking the display out of correct performance using settings that no one would use because the image will not look right. On top of that they do not use the checkerboard pattern and instead use on / off contrast ratio using a 100IRE white raster and then a 0IRE black raster. Some go even further by turning the display off and measuring what ever light remains for black which in many cases is none. Using these methods they can come up with very impressive numbers in their literature but they mean nothing for your application.
It is quite possible to have a display with an extremely high on / off contrast ratio yet have a poor or typical intra-field contrast ratio. In such a scenario that means the display will be very bright but the image will be washed out lacking dynamic range.
A figure that tells us a little bit more and has some value is lumens found in the Video Dictionary.