Thumbnailer takes timestamped images as input and produces a WebP animation that fits a given size constraint.
bazel build src:thumbnailer && bazel build src/utils:thumbnailer_compare
This tool reads a sequence of images and timestamps, and produces an animation in WebP format. By default, thumbnailer uses lossy compression and imposes the same quality factor to all frames.
./bazel-bin/src/thumbnailer [options] frame_list.txt -o=output.webp
bazel run src:thumbnailer [options] frame_list.txt -o=output.webp
frame_list.txt is a text file containing the description for each frame. Each line contains the frame's filename and its ending timestamp in millisecond, in the following format: filename timestamp. For example:
/anim1/frame01.png 150
/anim1/frame02.png 300
/anim1/frame03.png 450
/anim1/frame04.png 600
| Option | Default Value | Description |
|---|---|---|
-soft_max_size |
153600 | Desired (soft) maximum size limit (in bytes). |
-hard_max_size |
153600 | Hard limit for maximum file size (in bytes). |
-loop_count |
0 (infinite loop) | Number of times the animation will loop. |
-min_lossy_quality |
0 | Minimum lossy quality (0..100) to be used for encoding each frame. |
-m |
4 | Effort/speed trade-off (0=fast, 6=slower-better). Similar to cwebp -m. |
-allow_mixed |
false | Use mixed lossy/lossless compression. |
-algorithm |
equal_quality | Algorithm to generate animation {equal_quality, equal_psnr, near_ll_diff, near_ll_equal, slope_optim}. |
-slope_dpsnr |
1.0 | Maximum PSNR change (in dB) used in slope optimization. |
-verbose |
false | Print various encoding statistics. |
| Algorithm | Description | |
|---|---|---|
| 0 | equal_quality |
Generate animation setting the same quality to all frames, using binary search. |
| 1 | equal_psnr |
Generate animation so that all frames have the same PSNR. |
| 2 | near_ll_diff |
Generate animation allowing near-lossless method, impose different pre-processing factor to near-losslessly-encoded frames. |
| 3 | near_ll_equal |
Generate animation allowing near-lossless method, impose the same pre-processing factor to near-losslessly-encoded frames. |
| 4 | slope_optim |
Generate animation with slope optimization. |
The slope optimization algorithm terminates the binary search of equal_quality early if the PSNR increase is not worth the size increase. The extra byte budget can then be used for near-lossless encoding.
This tool takes the same list of frames as Thumbnailer, runs all algorithms, and prints several PSNR statistics (max PSNR increase, mean PSNR difference, etc.) with reference to -equal_quality.
./bazel-bin/src/utils/thumbnailer_compare frames_list.txt
Option -short condenses the printed message.
Unit tests of machine-generated image data, created with Google Test.
These tests are built as a binary:
bazel run test:thumbnailer_test
Run thumbnailer_test with valgrind to check for memory leaks and memory errors.
valgrind --leak-check=full --show-leak-kinds=all ./bazel-bin/test/thumbnailer_test