Using DBE in PixinsightLE.

[StargeezerTim]

Hi all,

 

its a long shot this as there cant be many using the LE version of pixinsight still! 

DBE mostly does a good job of removing gradients. Sometimes it leaves a Magenta cast but I can easy clear that up with colour balance. Sometimes though it severely darkens an image, pushing the histogram to the extreme left. I find it impossible to recover from this and was wondering if anyone knows of any perameters that I could change to prevent this happening?

 

Cheers, Tim. 

[wimvb]

Have you tried the 'normalize' checkbox in the lower panel? (I assume the interface looks the same as in the std version.)

[Uranium235]

You need to use a constant (try +30 as a start), that will ensure the histo has a gap before the black point. That is of course remembering to have done the DBE on the raw, cropped data (and not ran it on a stretched version).

You dont have to use PI to subtract the background model, Maxim or Ps can do that as well (Maxim offers better scaling options), or any other prog capable of pixel math - except the latter two allow you to preview the result quickly so you can make adjustments if required. To illustrate that, Ive just tested the supposition in Photoshop by subtracting a background model built in PI. The main issue being the bottom left to top right gradient.

Both images given the same DDP process and just levels, pretty rough but it works.

 

Before:

 

After subtraction in Ps (Calculations):

[StargeezerTim]

40 minutes ago, Uranium235 said:

You need to use a constant (try +30 as a start), that will ensure the histo has a gap before the black point. That is of course remembering to have done the DBE on the raw, cropped data (and not ran it on a stretched version).

You dont have to use PI to subtract the background model, Maxim or Ps can do that as well (Maxim offers better scaling options), or any other prog capable of pixel math - except the latter two allow you to preview the result quickly so you can make adjustments if required. To illustrate that, Ive just tested the supposition in Photoshop by subtracting a background model built in PI. The main issue being the bottom left to top right gradient.

Both images given the same DDP process and just levels, pretty rough but it works.

 

Before:

 

After subtraction in Ps (Calculations):

 

Thanks, it worked 

I used 'apply image' in PS. The only problem i had was that PI LE saved the background model image at about half the size of the original image so I had to reduce its size before I subtracted it. I'm sure I'll be able to work it out though as normally DBE'd files are same size as the originals.

Thanks... Tim. 

[Uranium235]

Yep, you need to set the DBE output to 1:1 - then your gradient model will be the same size as your original image. Takes a little longer to process, but its only a few seconds.

[StargeezerTim]

10 minutes ago, Uranium235 said:

Yep, you need to set the DBE output to 1:1 - then your gradient model will be the same size as your original image. Takes a little longer to process, but its only a few seconds.

Yep...I just worked it out... Another trick in the box... Many thanks... 

p.s. what is the DSO in the image, that is a beautiful scene...

[ollypenrice]

Butts in quickly!!  Seagull Nebula!

Olly

[StargeezerTim]

9 hours ago, ollypenrice said:

Butts in quickly!!  Seagull Nebula!

Olly

Thanks Olly... I can see an eagle with open wings... but a seagull will do!

[Xiga]

Hi there

You're certainly not the only one still using the old P.I LE, i too still use it for DBE! I'm sure the new modern version of P.I does it better, along with a myriad of other things, but for my own modest needs i find it does an absolutely fine job of cleaning up gradients. Speaking as someone who can still count the number of DSO's he's captured on one hand, and who has to use pretty much budget versions of everything, i for one am extremely thankful to still be able to use it. 

You probably already know most of this, but i'll share my method for getting to the gradient reduction stage of processing. As Already pointed out, gradient reduction needs to be done on Linear data, i.e before any stretching. 

1. Open the Autosave stacked file (i use DSS) in PS and immediately save as a new file (keep as 32 bit floating point, no compression).
2. Open this new file again in PS. Create a New Layer with massively increased Exposure to show cropping artifacts. Crop them out. Delete the Exposure Layer and Save. 
3. Open in P.I LE. Duplicate the image and bring up the Histogram tool. Click R-T to see changes in Real Time, and apply an aggressive stretch or two (i use the middle icon) to the duplicated image (usually Image02) enough to show up all the features of interest, stars, nebulosity etc. Don't be afraid to make it nice and bright, this won't affect the real image (usually Imag01).
4. The image is now bright enough for you to place the DBE sample points on Image02 without accidentally putting any on an area of interest. Play around with the Tolerance setting in DBE (try lowering it a little) so that when you place a sample point over the faintest of stars the shape is still just about picked up correctly. After placing all points (i use a lot, which does take ages!), drag the arrow onto the workspace to save the Process.
5. Now close Image02. Right-click the Process icon on the workspace and choose Launch Interface. Image01, which should still be extremely dark (hopefully you didn't apply any adjustments in DSS if that's what you use), should now be populated with all the sample points. Now Generate the background image (it should also come out extremely dark!). Then use PixelMath to subtract Image01_background image from Image01. Save. Also save the Process Icon too so you can re-use it if necessary!
6. After this you can move on to your favourite software of choice to do colour balance and stretching (i'm a PS guy myself).

 

[wimvb]

Why wouldn't you use dbe for this? It seems a lot more work this way.

[StargeezerTim]

18 hours ago, Xiga said:

Hi there

You're certainly not the only one still using the old P.I LE, i too still use it for DBE! I'm sure the new modern version of P.I does it better, along with a myriad of other things, but for my own modest needs i find it does an absolutely fine job of cleaning up gradients. Speaking as someone who can still count the number of DSO's he's captured on one hand, and who has to use pretty much budget versions of everything, i for one am extremely thankful to still be able to use it. 

You probably already know most of this, but i'll share my method for getting to the gradient reduction stage of processing. As Already pointed out, gradient reduction needs to be done on Linear data, i.e before any stretching. 

1. Open the Autosave stacked file (i use DSS) in PS and immediately save as a new file (keep as 32 bit floating point, no compression).
2. Open this new file again in PS. Create a New Layer with massively increased Exposure to show cropping artifacts. Crop them out. Delete the Exposure Layer and Save. 
3. Open in P.I LE. Duplicate the image and bring up the Histogram tool. Click R-T to see changes in Real Time, and apply an aggressive stretch or two (i use the middle icon) to the duplicated image (usually Image02) enough to show up all the features of interest, stars, nebulosity etc. Don't be afraid to make it nice and bright, this won't affect the real image (usually Imag01).
4. The image is now bright enough for you to place the DBE sample points on Image02 without accidentally putting any on an area of interest. Play around with the Tolerance setting in DBE (try lowering it a little) so that when you place a sample point over the faintest of stars the shape is still just about picked up correctly. After placing all points (i use a lot, which does take ages!), drag the arrow onto the workspace to save the Process.
5. Now close Image02. Right-click the Process icon on the workspace and choose Launch Interface. Image01, which should still be extremely dark (hopefully you didn't apply any adjustments in DSS if that's what you use), should now be populated with all the sample points. Now Generate the background image (it should also come out extremely dark!). Then use PixelMath to subtract Image01_background image from Image01. Save. Also save the Process Icon too so you can re-use it if necessary!
6. After this you can move on to your favourite software of choice to do colour balance and stretching (i'm a PS guy myself).

 

Thanks for your method Ciaran,

These days, I use two main approaches to gradients. For the simpler ones, I do it in PS, normally by duplicating the image (part stretched), blurring, then subtracting from the original using 'Apply image'. For trickier nebulas but where it seems a simple gradient, top to bottom or right to left, I'll duplicate layer, add a layer mask and put a gradient in the layer mask. For more complicated gradients, especially colour gradients, I'll create a background using DBE, tolerance of about .325. Then I'll save as a tiff and use the the 'apply image' function in PS. I find using PS to subtract the backgroung works much better and has more control than using PI to subtract, which often gives resulting images with a very strong Magenta cast. It also sometimes clips the black point.

Cheers, Tim.

 

p.s., that's all I use PI for, at the moment.