VideoProcessViewer

Compilation

Requires SFML (tested with 2.4), libpng, libjpeg and libtiff. The repository contains ImGui, ImGui-SFML and iio.

mkdir build
cd build
cmake ..
make
# the following command will install the binary 'vpv'
sudo make install
# or you can change your PATH variable with something like:
echo "export PATH=$PATH:`pwd`">~/.bashrc

Concepts

Sequence: ordered collection of images.

Window: zone to display one or more sequences. If multiple sequences are attached to a window, 'space' and 'backspace' are use to cycle between them.

View: indicate the portion of the image to display. Contains a center position and a zoom factor.

Player: indicate which image in the sequence should be displayed. Contains a few other parameters (check out the player GUI to see what it can do).

Colormap: transformation of the pixels of an image. Contains contrast/brightness (scale/bias) parameters (output=scale*pixel+bias) and a shader (to display optical flow, greyscale or color images).

By combining these concepts, VideoProcessViewer becomes a very convenient image/video viewer.

For example, if two sequences share the same view, the same window and the same player, you can visualize the differences between two videos by flipping between them (using 'space').

If you want to see both of them at the same time, attach the two sequences to different windows, and VideoProcessViewer will show them side by side, still keeping the view and timing synchronized.

If the images of multiple sequences don't have the same intensities (one between 0-255 and one between 0-1 for example), you can use two Colormap objects. They automatically adjust their parameters to normalize the image and fit its number of channels.

Command line arguments

Sequences can be specified either by escaped globbing (e.g. directory/my_images_\*.png) or by a single image (in this case, it will be a one image sequence). If the argument is a directory, a sequence containing every files of the directory is created.

nw, nv, np, nc are used as arguments to respectively create a new window, view, player or colormap for the following sequence. aw, av, ap, ac toggle the automatic creation of objects for each following sequences (for example, vpv 1.png nw 2.png nw 3.png x.png is equivalent to vpv aw 1.png 2.png 3.png aw x.png).

Display every images of the directory in the same window ('space' can be used to cycle through them):

vpv *.jpg

Display two sequences side by side:

vpv input_\*.png nw output_\*.png

Assuming results/ contains subdirectory such as results/noise=1/, results/noise=2/, ... with images in them, the following command will display these sequences and the groundtruth in different windows:

vpv aw results/*/ groundtruth/

Shortcuts

• number to bring focus to the n-th window.
• alt+number to bring focus to the n-th player.
• ctrl+L / shift+ctrl+L to cycle through layouts
• alt+L to disable the layout. This means you can resize (left click on the bottom right of the window) and move (right click and drag) windows freely.
• if a window is focused (blue title bar):
  • View
    • left click and drag to move the view.
    • z + wheel to change the zoom of the view.
    • i / o to zoom in and out. Clips to a power of two.
    • r to center the view and reset the zoom. shift+r to center and set the zoom to 1.
  • Colormap
    • a to automatically adjust contrast and brightness.
    • ctrl+a to smartly automatically adjust the contrast and brightness depending on the displayed content of the image.
    • shift+a to disable contrast/brightness modification (map to [0..1] or to [0..256] if the image has pixels >1)
    • mouse wheel to adjust the contrast.
    • shift mouse wheel to adjust the brightness.
    • shift mouse motion to adjust the brightness accordingly to the hovered pixel.
    • s / shift+s to cycle through shaders.
  • Player
    • p, left and right: see player's shortcuts.
  • , to save a snapshot of the image as it is displayed on screen. The file will be saved as 'screenshot_n.png'. This can be overriden by the environment variable SCREENSHOT.
• if a player is focused:
  • p to toggle playback.
  • left / right to display the previous/next frame of the sequence(s).
  • Settings can be changed using the Player GUI (alt+number or menu bar).
• q to quit VideoProcessViewer

Remarks

Despite its name, VideoProcessViewer cannot open video files. Use ffmpeg to split a video into individual frames. This may change in the future.

In order to be reactive during video playback, the frames are loaded in advance by a thread and put to cache. Currently the cache has no memory limit, but you can disable it by setting the environment variable 'CACHE' to '0' (env CACHE=0 vpv [args]) or press F11. To automatically invalidate the cache when a file is changed on disk, a filesystem watcher can be enabled using the environment variable 'WATCH' (env WATCH=1 vpv [args]). For now, F11 can also be used to flush the cache manually.

Similarly to the previous remark, the globbing expansion is only done at startup. If new images are saved to disk, VideoProcessViewer won't see them (except if you update the globbing in the sequence GUI). This will change in the future.

VideoProcessViewer is not a great software name. This may change in the future.

Related projects

pvflip (VideoProcessViewer is heavily inspired by pvflip)

G'MIC