How to change the background of a Ha solar image to black?

Rick Veregin · Mar 20, 2026, 03:52 PM

Hi Luke

I’m assuming the raw image had a black background and a bright sun, then yes, the processing was odd in imppg. It is easiest to do what you want to do in imppg, use GIMP just to do any final small tweaking. In imppg you need to apply a special tone curves adjustment and it can be finicky. Also need to be careful in imppg, as messing up the tone curve causes imppg to crash.

I assume you are processing a 16 bit uncompressed file, not a jpg—very hard to do with an 8 bit compressed file.

Here is a tutorial on using imppg. At the end it shows an example of a tone curve. https://greatattractor.github.io/imppg/tutorial/tutorial_en.html#introduction

The immpg tone curve below shows one solution, the peak at the left is the prominces, so put the first point at the start of the prominences at zero, the gap from the left is the background—you need a gap or your background will not be black. The curve goes up to enhance the prominences, then comes down to invert the surface, the brighter the solar surface, the darker and vice versa. You can also adjust gamma. Note the tone curve may need to be sharper at the left if your prominences are weak, and sometimes you need a dip in the curve between the prominence peak on the left and the solar surface peak which runs center to right.

Hope this helps,

Rick

📷 image.png

Thanks for your help Rick. I have gone back through and made a more pleasing photo with this inversing method. My curve however looks more bumpy. I think the background issue is mostly because of the light scattering on the camera side of things because there was a thin layer of cloud out when I took the image. I am very pleased with it as my first solar image, and I am expecting better conditions tomorrow so I should be able to improve on this.

📷 image.png📷 Solar disk re process.jpg

Luke Pearson · Mar 20, 2026, 04:38 PM

Rick Veregin · Mar 20, 2026, 03:52 PM

Hi Luke

I’m assuming the raw image had a black background and a bright sun, then yes, the processing was odd in imppg. It is easiest to do what you want to do in imppg, use GIMP just to do any final small tweaking. In imppg you need to apply a special tone curves adjustment and it can be finicky. Also need to be careful in imppg, as messing up the tone curve causes imppg to crash.

I assume you are processing a 16 bit uncompressed file, not a jpg—very hard to do with an 8 bit compressed file.

Here is a tutorial on using imppg. At the end it shows an example of a tone curve. https://greatattractor.github.io/imppg/tutorial/tutorial_en.html#introduction

The immpg tone curve below shows one solution, the peak at the left is the prominces, so put the first point at the start of the prominences at zero, the gap from the left is the background—you need a gap or your background will not be black. The curve goes up to enhance the prominences, then comes down to invert the surface, the brighter the solar surface, the darker and vice versa. You can also adjust gamma. Note the tone curve may need to be sharper at the left if your prominences are weak, and sometimes you need a dip in the curve between the prominence peak on the left and the solar surface peak which runs center to right.

Hope this helps,

Rick

📷 image.png

Thanks for your help Rick. I have gone back through and made a more pleasing photo with this inversing method. My curve however looks more bumpy. I think the background issue is mostly because of the light scattering on the camera side of things because there was a thin layer of cloud out when I took the image. I am very pleased with it as my first solar image, and I am expecting better conditions tomorrow so I should be able to improve on this.

📷 image.png📷 Solar disk re process.jpg

Glad I could be of help. Yes, as I said, you may need to do even more complex tone curves, depending on your data.

Luke’s comments are right on, the hot spot should be centered on the centre of the Sun. And solar is very unforgiving, even light haze scatters a lot of light, wiping out the prominences. Assuming you have live view when you are recording the images you should be able to see the prominences, do a strong stretch on your live view, let the disk go totally overexposed. This can help when you are trying to tune the wavelength.

Rick

Rick Veregin · Mar 20, 2026, 08:05 PM

Luke Pearson · Mar 20, 2026, 04:38 PM

Rick Veregin · Mar 20, 2026, 03:52 PM

Hi Luke

I’m assuming the raw image had a black background and a bright sun, then yes, the processing was odd in imppg. It is easiest to do what you want to do in imppg, use GIMP just to do any final small tweaking. In imppg you need to apply a special tone curves adjustment and it can be finicky. Also need to be careful in imppg, as messing up the tone curve causes imppg to crash.

I assume you are processing a 16 bit uncompressed file, not a jpg—very hard to do with an 8 bit compressed file.

Here is a tutorial on using imppg. At the end it shows an example of a tone curve. https://greatattractor.github.io/imppg/tutorial/tutorial_en.html#introduction

The immpg tone curve below shows one solution, the peak at the left is the prominces, so put the first point at the start of the prominences at zero, the gap from the left is the background—you need a gap or your background will not be black. The curve goes up to enhance the prominences, then comes down to invert the surface, the brighter the solar surface, the darker and vice versa. You can also adjust gamma. Note the tone curve may need to be sharper at the left if your prominences are weak, and sometimes you need a dip in the curve between the prominence peak on the left and the solar surface peak which runs center to right.

Hope this helps,

Rick

📷 image.png

Thanks for your help Rick. I have gone back through and made a more pleasing photo with this inversing method. My curve however looks more bumpy. I think the background issue is mostly because of the light scattering on the camera side of things because there was a thin layer of cloud out when I took the image. I am very pleased with it as my first solar image, and I am expecting better conditions tomorrow so I should be able to improve on this.

📷 image.png📷 Solar disk re process.jpg

Glad I could be of help. Yes, as I said, you may need to do even more complex tone curves, depending on your data.

Luke’s comments are right on, the hot spot should be centered on the centre of the Sun. And solar is very unforgiving, even light haze scatters a lot of light, wiping out the prominences. Assuming you have live view when you are recording the images you should be able to see the prominences, do a strong stretch on your live view, let the disk go totally overexposed. This can help when you are trying to tune the wavelength.

Rick

Thanks. I will do. I have heard however that tuning is quite tricky because if you tune for prominences you loose details on the surface and vise versa. Is this true?

Luke Pearson · Mar 20, 2026, 08:40 PM

·

·

·

Hi Luke

I’m assuming the raw image had a black background and a bright sun, then yes, the processing was odd in imppg. It is easiest to do what you want to do in imppg, use GIMP just to do any final small tweaking. In imppg you need to apply a special tone curves adjustment and it can be finicky. Also need to be careful in imppg, as messing up the tone curve causes imppg to crash.

I assume you are processing a 16 bit uncompressed file, not a jpg—very hard to do with an 8 bit compressed file.

Here is a tutorial on using imppg. At the end it shows an example of a tone curve. greatattractor.github.io/.../tutorial_en.html...

The immpg tone curve below shows one solution, the peak at the left is the prominces, so put the first point at the start of the prominences at zero, the gap from the left is the background—you need a gap or your background will not be black. The curve goes up to enhance the prominences, then comes down to invert the surface, the brighter the solar surface, the darker and vice versa. You can also adjust gamma. Note the tone curve may need to be sharper at the left if your prominences are weak, and sometimes you need a dip in the curve between the prominence peak on the left and the solar surface peak which runs center to right.

Hope this helps,

Rick

📷 image.png

Thanks for your help Rick. I have gone back through and made a more pleasing photo with this inversing method. My curve however looks more bumpy. I think the background issue is mostly because of the light scattering on the camera side of things because there was a thin layer of cloud out when I took the image. I am very pleased with it as my first solar image, and I am expecting better conditions tomorrow so I should be able to improve on this.

📷 image.png📷 Solar disk re process.jpg

Glad I could be of help. Yes, as I said, you may need to do even more complex tone curves, depending on your data.

Luke’s comments are right on, the hot spot should be centered on the centre of the Sun. And solar is very unforgiving, even light haze scatters a lot of light, wiping out the prominences. Assuming you have live view when you are recording the images you should be able to see the prominences, do a strong stretch on your live view, let the disk go totally overexposed. This can help when you are trying to tune the wavelength.

Rick

Show more

Thanks. I will do. I have heard however that tuning is quite tricky because if you tune for prominences you loose details on the surface and vise versa. Is this true?

I have a double stack Lunt, not sure how yours compares. So I have a tuner at the back, which is pressure tuned, and then the double stack is in front of the objective is tilt tuned. So without the front unit on, I tune the back pressure tuner to make it as dark as possible on the histogram, you are rejecting the most off-band sunlight. Then I put on the front tuner and tune for the brightest image, this means the front tuner is matched with the back. Finally, I fine tune the front tilt so the brighest part is centered on the Sun, if it is not centered one side will be brighter than the other.

This tuning method is easy and it always works, anything else I tried was just back and forth and never sure I got it right.

So I can’t answer your question directly, as this method is really an overall surface tuning, which is where most of the signal comes from. Though I do get a good result for the surface and prominences with my all in one tuning.

My suspicion is this advice for tuning to surface or proms is for visual viewing. Because yes the prominences will not be as bright when tuned for the surface, which matters visually. But since we can collect lots of images we can get good S/N in the proms, even if not perfectly tuned to them.

Rick

Luke Pearson · Mar 20, 2026, 08:42 PM

I am also going to make the disc mosaic with my barlow for proper sampling.

Hi,

Tuning on a disc and tuning on a partial solar image is a different thing.

If you have a partial Sun image then tuning is a bit easier…

Before venturing into assembling Sun mosaic I would recommend tune the filters on the complete sun disc. This will help you gain more experience in tuning the filters.

Rainer

Luke Pearson · Mar 21, 2026, 02:16 AM

solarmax III

If I recognize well the scope you have an etalon inside the scope and a front etalon. Correct?

The front etalon as far as I know has also a tilt mechanism which is a tiby golden wheel with which you chage the inclination of the front etalon. correct?

If that is the case, leave the roch view tuner in the middle position and rotate the tiny golden wheel in such way that the fron etalon has 0 zero tilt or inclination.

Now move the lever in the telescope body and see what happens. If they behave like mine the the hotspot should move.

Then you can start tilting the front etalon and forget for a while rotating the rich view adjuster.

The tuning of a double stacked Ha filter is a Trial & Error process and looking what happens when you move what is the key for tuning and learning wht does each of the movements.

I once had a rich view tuned Ha for test here and honestly in my case rotating the front ring did not do anything in my case. Just my experience with a Rich View tune system.

Rainer

PS Are you a member of SolarChat Forum? There are many solar imagers with more experience than me.

Rainer Ehlert · Mar 21, 2026, 02:47 AM

Luke Pearson · Mar 21, 2026, 02:16 AM

solarmax III

If I recognize well the scope you have an etalon inside the scope and a front etalon. Correct?

The front etalon as far as I know has also a tilt mechanism which is a tiby golden wheel with which you chage the inclination of the front etalon. correct?

If that is the case, leave the roch view tuner in the middle position and rotate the tiny golden wheel in such way that the fron etalon has 0 zero tilt or inclination.

Now move the lever in the telescope body and see what happens. If they behave like mine the the hotspot should move.

Then you can start tilting the front etalon and forget for a while rotating the rich view adjuster.

The tuning of a double stacked Ha filter is a Trial & Error process and looking what happens when you move what is the key for tuning and learning wht does each of the movements.

I once had a rich view tuned Ha for test here and honestly in my case rotating the front ring did not do anything in my case. Just my experience with a Rich View tune system.

Rainer

PS Are you a member of SolarChat Forum? There are many solar imagers with more experience than me.

Hi, thanks for your help. I will check out that forum now. This is my telescope. I spent a while tuning it and noticing the contrast differences and how it varied depending on the suns placement on the sensor too. Learnt a lot but still have much to improve!

📷 WhatsApp Image 2026-03-21 at 15.43.08.jpeg