Apply stretch to frames/movies

[nic_doebelin]

Hi,

I am using SharpCap with an ASI178MC camera to film a scientific experiment (non-astro). It would be helpful if the display histogram stretch could be applied to the saved frames or video files. Namely a gamma correction applied to the output files would be helpful, but I haven't managed to do it. Is it possible somehow?

Thanks,
Nic

[admin]

Hi Nic,

it's not possible for videos I'm afraid. For single frames, there is a 'save' button in the mini histogram area, and the function of that button is to save the image exacly as shown on screen. There are a couple of limitations though

* Image will be saved as 8 bit, even if camera in highter bit depth mode
* Image will be saved as PNG

These are both because the main purpose is to save a version of the image as currently seen (not intending to process further), so an 8bit depth and an easy to view format are selected.

Is that any help? In general it's considered best to save without that sort of digital 'gamma' or similar applied to the data as once that sort of transformation is applied it is usually impossible to undo it properly.

cheers,

Robin

[Jean-Francois]

Hello Nic,

You can use the Camera Controls (for QHY camera) and set the gamma, brightness and contrast.
The images or films will be saved with these settings.
But, you can not go back (easily). The gamma transformation is not linear.

Image_Controls.jpg

Other camera brand has maybe different name of function.

Jean-Francois

[nic_doebelin]

Hi Nic,

it's not possible for videos I'm afraid. For single frames, there is a 'save' button in the mini histogram area, and the function of that button is to save the image exacly as shown on screen. There are a couple of limitations though

* Image will be saved as 8 bit, even if camera in highter bit depth mode
* Image will be saved as PNG

These are both because the main purpose is to save a version of the image as currently seen (not intending to process further), so an 8bit depth and an easy to view format are selected.

Is that any help? In general it's considered best to save without that sort of digital 'gamma' or similar applied to the data as once that sort of transformation is applied it is usually impossible to undo it properly.

cheers,

Robin

Hi Robin,

Thanks a lot for your reply. I understand that SharpCap is designed for Astro use, but it turned out to be very useful for my non-astro application, too. I was a bit concerned that applying a strong gamma correction after saving an 8bit AVI would cause severe banding, but it looks fine. So I will continue applying the correction with ffmpeg in post-processing.

Theoretically I could save a 16bit SER movie, but since I need to record for hours (at low fps, though), the storage requirements are just insane.

Thanks again.
Cheers,
Nic

[nic_doebelin]

Hello Nic,

You can use the Camera Controls (for QHY camera) and set the gamma, brightness and contrast.
The images or films will be saved with these settings.
But, you can not go back (easily). The gamma transformation is not linear.

Image_Controls.jpg


Other camera brand has maybe different name of function.

Jean-Francois

Hi Jean-Francois,

Thanks for your reply. Indeed I was confused because I saw the gamma slider in the camera controls on some screenshots, but I couldn't find it on my computer. It turns out that my ASI 178MC doesn't allow gamma correction in camera, just brightness and contrast. That is why the gamma slider is not shown. I will have to stick to post processing, but it works reasonably well and I don't see any banding despite the strong gamma correction.

Cheers,
Nic