Data Compression


Criteria

Survey Formats

Basics

Compression Methods

Data Formats

Files

Audio Data

Image Data

GIF

JPEG

Characteristics

Fields of Application

Coding Steps

Image Preparation

Transformation

Quantization

Entropy Coding

Compatibility

Video Data


Glossary

Index


Download


www.BinaryEssence.com

JPEG: Image Preparation


A JPEG file consists of separated components, which are processed independently from each other. Contents and resolution of the components could differ depending on application and quality requirements.


The most common format is YUV using the two colour components U and V and the brightness component Y. Depending on the desired image quality the resolution of the colour components could be reduced, for example by the factor two or four; i.e. beside the full brightness information two or four pixels will be combined together to one colour information.


This approach results from the selective sensitivity of the human eye for the perception of differences in colour and brightness.


The brightness is substantially of higher importance for the total perception. Therefore it is recommended to provide a proportionally larger part of the data volume for the encoding of the brightness. These procedures are called 4:2:2 or 4:1:1 subsampling.


DCT


 <   ^   > 

JPEG: Coding Steps JPEG: Coding Steps JPEG: Transformation (Discrete Cosine Transform, DCT)