Hi Anh,

Happy to hear that you find this application useful.
The story behind the image export looking different from what you see on the display is that the exported images show the area covered by your image inside the atlas. So even if your image is 3000x4000 pixels large, the export is still going to result in something like 400x350 pixels (the atlas has 512x512 pixels in a coronal plane). To combine the two, you can simply stretch the exported image over the real one in some image manipulation software (practically drag its bottom-right corner to the bottom-right corner of the corresponding histological image, and you will suddenly see what was in QuickNII).

I hope this helps.
Best regards,
Gergely