When to use DBE?

[davenash]

Hi, all.

Like many here I am a great fan of PI LE, and I especially use DBE to remove glow and vignetting from my images.

I have a general question regarding when in the workflow DBE should be used.  Specifically, should it be the first thing done to a raw image, or should levels (histogram transformation) be done first?

What do people think or normally do?

Regards

Dave

[Carlos Milovic]

Hi Dave

Sorry for the delay.

I believe that vignetting correction, and any gradient removal, is the first thing to. Sometimes, it is a must before any image integration process.
The reason: it is best to calibrate our data before we play with it. For sure, any initial histogram adjustement becomes obsolete after this procedure. Also, you may even destroy data, unwillingly.

So, as conclusion, first is the calibration, later the brightness and contrast adjustments (histograms, curves, etc.)... and even later the noise reduction.

By the way, another good question is when to apply deconvolutions... but since you don't have this process avalaible, yet (it has been in our standard beta releases for two years), let's keep it as a pending answer  :D

[davenash]

Thanks for the advice, Carlos, it makes a lot of sense.

I will bear it in mind when processing my images.

Dave

[Anonymous]

Dear Carlos,

I am a new user of PixInsight, therefore the answer may be given elsewhere, but I could not find it:

I find it hard to apply the Dynamic Background Extraction as a first step as the raw image in most cases is more or less dark. Therefore, defining the correct point for the background determination is not easy and the result may be erroneous.

The same problem may arise with other image enhancement steps on a image which has not already been histogram manipulated.

What is your advise?

Thanks for your help

[Carlos Milovic]

Hi guest :)

The best solution for your problem would be to use some stretching function, that lets you see the image with different contrast and brightness, while the pixel values remain the same. Unfortunably, this function has not been implemented in the LE release, althought it will be included in the next standard edition, wich will be avalaible soon as a beta public release.
Anyway, there are some tricks that you may try, taking advance of the flexibility and power that PI LE currently gives you.

First, duplicate your image (or save it, or make a preview of the whole image and then a new image from it). Now apply the histogram and curves adjustments you want. This will be the image you have to use to set the sample boxes of the DBE instance. So, launch DBE on this image, and set all the boxes as you want. When you are ready, instead of generating a new background model, create a process icon (drag the "<" symbol and drop it in PI's workspace). Now abort the DBE instance.
At this time, you have to go back to the original image (you may use the revert command, if you worked over the original image). Make it active by left-clicking on it's window. Double-click the DBE process icon to launch the previous DBE instance over this image. Now, you'll see that all the sample boxes defined before are here. Change the values of the tolerance, smoothness, etc., and generate the new model.
If you need to "see" the results with a histogram manipulation, repeat the firsts steps with the result of applying the DBE model (use PixelMath and tell it to create a new image instead of replacing the current values).

This is a bit time consuming, but will lead you to the most accurate results. Just remember this advice: use process icons as much as you can!

[Wulf]

Dear Carlos,

thats exactly the advice I needed. Thank you very much.

Nevertheless, I agree, that the possibility of stretching the histrogramm of the displayed picture without affecting the raw data will be a key-function to improve the straight forward capabilities of the software.

Best regards from Germany
Wulf