Histogram Transformation --> Auto stretch not producing the same result as AutoStretch mode

[pcb.astro (Pankaj Bhambhani)]

Hi,

I’m a beginner astrophotographer and first time Siril user. I’m using Siril 1.0.6 on my Mac for processing images of the Comet ZTF. After doing all the stacking and processing, I want to save my image so I can process it in gimp. Before saving when I try to apply the auto-stretch algorithm (from histogram transformation), I get a different result than what I see in the AutoStretch mode.

My image looks like this in Linear mode

It looks like this in AutoStretch mode

But become all white when applying the auto stretch algorithm in Image Processing → Histogram Transformation

Any advice is appreciated.

[vinvin (Vincent Hourdin)]

Hello, how is displayed the white image you show? Is it in siril or gimp, in linear rendering?

[pcb.astro (Pankaj Bhambhani)]

The white image is displayed so in siril, in linear rendering

[lock042]

Check for the viewer sliders

[pcb.astro (Pankaj Bhambhani)]

@lock042 I’m not sure what a viewer slider is, I’m attaching a screenshot of the histogram as it looks after pressing the “appl the auto-stretch” button. There does seem to be a spurious blue peak at the left edge. But I have tried adjusting the shadows and midtones, yet I don’t get quite the result that I get if I view the image in auto-stretch mode.

[lock042]

On the screenshot you sent, you have low value at 96 and high value at 124.
So this is perfectly normal to see something white. You need to push these sliders to their min and max.

You should have a look to our tutorials where everything is explained.

[pcb.astro (Pankaj Bhambhani)]

@lock042 thank you, it seems the sliders had those value because the adjacent radio group had the option “MIPS-LO/HI” selected by default. I changed it to the “Min/Max” radio button, and now things work as expected.