Image Cropping

[scriptorron]

Versions >2.9.0 will support image cropping. With this feature you can

1. select a smaller image area when taking pictures

2. do auto guiding with a small region around the guiding star

At the day of writing these lines the cropping implementation has some limitations:

• It is not fully tested. I successfully tested the implementation with the EKOS camera tab and binning=1. But there is still a risk that some clients have different understanding of image origin and size. Furthermore it is not tested on a Pi Zero and I hope, the cropping will not cost too much CPU and RAM.
• It will likely not work with binning>1. My reference for feature functionality is the indi_simulator_ccd and I spend hours to find out how things are implemented there. It seems, that indi_simulator_ccd relates image size and origin to the un-binned sensor and applies the binning after cropping. For instance when you set size W=600 H=400 and binning=2 the indi_simulator_ccd will deliver an image of size 300x200. Doesn't that complicates the calculation on client side? Anyway, it is the established behavior and I have to follow it. The problem in indi_pylibcamera is, that the camera hardware does the binning and the driver needs to do the cropping afterwards. Off course, the driver knows the binning setting, but some cameras (like IMX477) do automatically an additional cropping on binned images. The cropping done by indi_pylibcamera must consider this additional cropping done by the camera. Unfortunately this is difficult to find out from the information provided by the camera. The current implementation in indi_pylibcamera applies the cropping on the image comming from the camera and ignores if the camera does binning or not.
• The cropping is done in the driver with Python code. This costs some computational time and you will not save RAM. But you still have the advantage of transmitting smaller images to the client.

I hope the cropping feature is useful for you.