ASCOM DSLR Stretch too dark

[Doug Henderson]

Hello, this is really a question, but I cannot find any documentation on this.

I have written an ASCOM driver for Sony cameras.

This driver uses libraw to extract the RAW pixel data from photos and passes this back to NINA as bayered RGGB data.

I have a user who is saying that the preview images displayed by NINA are “too dark” even with auto-stretch applied. If I compare the auto-stretch that NINA does with another app, the NINA version is definitely much darker. Increasing the “autostretch factor” does result in a brighter image, but it seems to be just a general brightening of the image.

Given that the raw data from the camera is by necessity unmodified (else it wouldn’t be raw anymore), I’m wondering if there is something I’m missing here, or if the ASCOM interface just doesn’t expose enough image meta-data to generate a better preview.

Below is an example - two shots, taken with exact same camera settings within 30 seconds of each other, both with auto-preview (one in NINA, one in APT).

If necessary I can use exactly the same image (that would result in exactly the same RGGB data) if there are any concerns about the test environment.

Any thoughts? Thanks very much.

Doug

[Stefan B]

It’s hard to see the histogram of the image taken. Possibly the histogram is above 25% and the autostretch will always “stretch” the image to the 25% regardless of it being above or below that.

[Stefan B]

As my understanding is that the stretch is just reducing the brightness because it is overexposed, its not an issue.