How would I change the exposure of a series of images with ffmpeg while compiling into an MP4, please give a command line example.
To change the exposure of a series of images using ffmpeg, you can use the "curves" filter. This filter allows you to adjust the brightness and contrast of an image.

Here is an example command that changes the exposure of a series of images and compiles them into an MP4:
``` 
ffmpeg -i image-%d.png -vf "curves=levels=0:0.5:1" -c:v libx264 -pix_fmt yuv420p output.mp4
``` 
In this command:

- image-%d.png specifies the input images, where %d is a placeholder for the frame number.
- curves=levels=0:0.5:1 specifies the "curves" filter and sets the exposure to 0.5. The levels parameter takes three values: the minimum input level, the middle level, and the maximum input level. In this example, 0:0.5:1 means that the minimum input level is 0, the middle level is 0.5, and the maximum input level is 1.
- libx264 specifies the H.264 video codec to be used for encoding the output video.
- yuv420p specifies the pixel format for the output video.
- output.mp4 is the name of the output file.

Note that this is just one example, and you can adjust the exposure further by changing the values in the "curves" filter.