With very low shading content in the image you have an alternative method to homogenize the image transitions between the single tiles.

1. Under Image Parameters in the Input tool select the tile image for the stitching.
2. In the Parameters tool, click on the New Output button.
3. Activate the Fuse Tiles checkbox.
   
4. Click on the Apply button to start the processing.

1. This function will smoothly average all edge regions of the tiles via their grey values in order to avoid sharp edges. With high background shading this function alone will not be sufficient.