HRTEM is a useful technique to observe the structure of coal char at an atomic level. To analyze the char structure quantitatively, we developed a new filtration technique for HRTEM images and a computer algorithm to obtain information such as the graphene layer size, interlayer spacing, the number of layers per stack, and its distribution from the post-filtered extracted HRTEM images. By using a computerized imaging system and image analysis algorithm, it is possible to analyze many images from different sample spots, which helps to make the analyzed result as general as possible. The aim of this article is to describe the usefulness of the technique to analyze the structure of carbonaceous materials. We applied this technique to study quantitatively the crystallinity of Pocahontas coal chars gasified in CO2 up to various conversion levels at 1200 degrees C. TEM observation showed a remarkable structural change during the gasification.