Automatic Text Line Segmentation Directly in JPEG Compressed Document Images

TL;DR

This paper introduces methods for directly performing text line segmentation on JPEG compressed images by analyzing DCT coefficients, eliminating the need for full decompression and improving efficiency in processing large volumes of document images.

Contribution

It presents two novel approaches for text line segmentation directly in JPEG compressed domain, one with partial decompression and another using analysis of AC coefficients without decompression.

Findings

Effective segmentation across various font sizes and styles

Avoids full decompression, reducing computational cost

Achieves good performance in diverse document conditions

Abstract

JPEG is one of the popular image compression algorithms that provide efficient storage and transmission capabilities in consumer electronics, and hence it is the most preferred image format over the internet world. In the present digital and Big-data era, a huge volume of JPEG compressed document images are being archived and communicated through consumer electronics on daily basis. Though it is advantageous to have data in the compressed form on one side, however, on the other side processing with off-the-shelf methods becomes computationally expensive because it requires decompression and recompression operations. Therefore, it would be novel and efficient, if the compressed data are processed directly in their respective compressed domains of consumer electronics. In the present research paper, we propose to demonstrate this idea taking the case study of printed text line segmentation. Since, JPEG achieves compression by dividing the image into non overlapping 8x8 blocks in the pixel domain and using Discrete Cosine Transform (DCT); it is very likely that the partitioned 8x8 DCT blocks overlap the contents of two adjacent text-lines without leaving any clue for the line separator, thus making text-line segmentation a challenging problem. Two approaches of segmentation have been proposed here using the DC projection profile and AC coefficients of each 8x8 DCT block. The first approach is based on the strategy of partial decompression of selected DCT blocks, and the second approach is with intelligent analysis of F10 and F11 AC coefficients and without using any type of decompression. The proposed methods have been tested with variable font sizes, font style and spacing between lines, and a good performance is reported.