Hi, I'm afraid this kind of thing just doesn't work at the moment. The principal difficulty is that our HDR implementation works by having different "channels", for example there's a "default" channel, the "HDR long exposure channel", the "HDR short exposure channel" and so on. What we really want here is the ability to set the exposure time and gain in some of these other channels, but unfortunately at the current time libcamera just doesn't have APIs for this kind of thing, so controls only work on the "default" channel. We did begin this discussion some time ago, but there's not been any progress. It's not as simple as "just add the missing camera controls", the problem is more that the form this API takes just isn't well suited for the way our HDR works.
Also, though perhaps less significant at this point, is that libcamera-still isn't good for capturing HDR stills as it doesn't know that it needs to wait to accumulate multiple frames (it works better with libcamera-hello or libcamera-vid). You would do better moving to Python where you can easily insert delays like this.
I think there may be some ways forward, however.
Firstly, I'd have thought that if your scene is really dark then the auto-AGC on the HDR channels should drive the exposure and gain as high as possible, meaning you don't need to set the exposure yourself. You would have to make sure that you're not limiting the framerate, nor that the exposure profiles are clamping the exposure either (that's in the tuning file).
Another thought is that I think you can tell the HDR to use channel 0 (the "default" channel) as the short metering channel. Then you could set the exposure explicitly there. However, I've never tried this so can't totally promise as to what would happen, but it would be an interesting experiment!
Also, though perhaps less significant at this point, is that libcamera-still isn't good for capturing HDR stills as it doesn't know that it needs to wait to accumulate multiple frames (it works better with libcamera-hello or libcamera-vid). You would do better moving to Python where you can easily insert delays like this.
I think there may be some ways forward, however.
Firstly, I'd have thought that if your scene is really dark then the auto-AGC on the HDR channels should drive the exposure and gain as high as possible, meaning you don't need to set the exposure yourself. You would have to make sure that you're not limiting the framerate, nor that the exposure profiles are clamping the exposure either (that's in the tuning file).
Another thought is that I think you can tell the HDR to use channel 0 (the "default" channel) as the short metering channel. Then you could set the exposure explicitly there. However, I've never tried this so can't totally promise as to what would happen, but it would be an interesting experiment!
Statistics: Posted by therealdavidp — Mon Mar 11, 2024 9:46 am