Near-focus with narrow-band imaging is a novel technique to improve the quality of images of the irregular mucosal structures and microvessels of gastric neoplasms. The investigators compare this technique with indio carmin spray, commonly used tool to determine tumor margin. The subject are patients who underwent endoscopic submucosal dissection for gastric neoplasms. Participants are randomized into near-focus with narrow-band imaging and indigo carmin groups. First, marking is performed at the tumor margins determined by each modality. The distance from the marking dots to the tumor margin is measured histopathologically in the resected specimens. Finally, the investigators will compare the accuracy between two groups based on the distance from marking dots to tumor margin measured by histopathologic examination.

Inclusion Criteria:

• Participants who undergo endoscopic submucosal dissection for gastric tumors (early gastric carcinoma or gastric adenoma)

Exclusion Criteria:

• fail to en bloc resection