skyfill

README

Skyfill

Most drones (UAVs) cannot look straight up to photograph the sky above them. As a result, spherical panoramas made with drones tend to have a gap in the sky. Some drones, like the DJI Mavic 2, can fill in this gap automatically while generating a preview. Skyfill allows you to do fill in those gaps in the sky in high-resolution images.

Download Skyfill

Skyfill releases can be downloaded from Gitlab.

Example Images

Before (left/above) and after (right/below) applying Skyfill with the default options.

Basic Usage

Skyfill reads 8-bit PNG, TIFF, and JPEG files. It writes 8-bit JPEG files if the input is 8-bit, and 16-bit TIFF files if the input is 16-bit. It assumes the colour space is sRGB, unless the -adobergb parameter is used.

The basic way to run Skyfill is skyfill input-file.png. On Windows it is possible to simply drop an image file onto the skyfill.exe file.

Mirror Ball

The sky part can be made a bit more interesting by creating a so-called mirror ball that reflects the ground. This results in a mini planet version of the panorama, hanging in the sky. To see what it looks like, check https://stuvelfoto.nl/panorama/tulpen-rood-geel-120m-mirrorball/

Run Skyfill with skyfill -mirrorball input-file.png to enable this mode.

Advanced Usage

There are several commandline options to influence the result:

• -out {format}: Choose a format of auto, jpeg, png, or tiff. This will determine the output format written. Format auto will use JPEG for 8-bit files, and TIFF for 16-bit files.
• -adobergb: Use this if the input is in AdobeRGB to have slightly better blending of the sky.
• -lower-sky {percentage}: Skyfill automatically detects the edge of the sky gap by finding black or transparent pixels. This option lowers the detected edge by a percentage of the detected gap height. For example, if you want to lower where Skyfill starts filling in the sky gap by 10% of the gap height, use -lower-sky 10.
• -blend {percentage}: To prevent a hard edge between the photographed sky and the generated sky, Skyfill uses 10% extra space to blend between them. If you want a smoother blend, for example 20%, use -blend 20. To see the hard edge use -blend 0.
• -quality Control the quality of JPEG output. Values from 0 to 100 can be used.
• -quiet: Show less information on the terminal (only warnings and errors).
• -help: Show all available commandline options, then quit.

With 80% blend size (left/above), and with a 50% (middle) and 80% (right/below) lower sky edge.

When passing those parameters, do so before the input image filename. For example: skyfill -lower-sky 20 -blend 30 input-image.png

Debugging

For debugging purposes these options can be used:

• -bounds: Draws a horizontal line to indicate the lower bound of the sky gap, and another line to indicate the lower bound of the blend area (a.k.a. "extra sky", see -blend above). It also draws a blend weight indication in the blend area.
• -samples: Draws a red dot on each sample point of the generated sky. The sky colours are interpolated linearly between those sample points.
• -debug: enable debug logging.

Copyright & License

Copyright © 2019 by Sybren A. Stüvel.

Skyfill is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

Skyfill is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with Skyfill. If not, see https://www.gnu.org/licenses/.

The images used in this documentation are created by and copyright © 2019 by Sybren A. Stüvel. They can be freely distributed but only used or otherwise displayed as part of documentation for or demonstration of Skyfill, and any usage must credit Sybren A. Stüvel as the photographer.