Pixinsight for dummies!

[RetroArchangel]

How do I save an image in Pixinsight with the histogram stretch applied? I am using Histogram Transformation not STF. I end up having to stretch again in Photoshop which must be wrong? Image looks exactly how I want it in Pixinsight, but when viewed after saving looks very dark and dowdy. I have tried Googling, but maybe using the wrong terminology. Driving me insane!

Thanks

Andy

[ollypenrice]

You may just be looking at the Real Time Preview of the stretch? You need to apply it to the image itself, not the preview. Drag the little triangular icon on the bottom left of the HT window onto the image to save it. Again, this is the image and not the preview. Other than that I can't think of what it might be.

Olly

[RetroArchangel]

You may just be looking at the Real Time Preview of the stretch? You need to apply it to the image itself, not the preview. Drag the little triangular icon on the bottom left of the HT window onto the image to save it. Again, this is the image and not the preview. Other than that I can't think of what it might be.

Olly

It has definitely been applied to the image and not the live preview. Could it be the downscaling from 32bit per channel to 8bit to save it as a jpg?

[IanL]

I suspect that you already had a screen transfer function (STF) active before you started the histogram transformation process.  Once you start the real-time preview of the histogram transformation, any active STF is applied to the preview in addition to changes you make to the histogram. When you apply the histogram transformation to the image (by dragging the blue triangle to the image), the same thing happens, i.e. the image is modified with the stretched histogram, but it is still displayed with the active STF as well.

Now when you save the image and re-open it later, you no longer have an active STF applied so you only see the changes from the histogram transformation (which will have been very small, since you were fooled by the STF being applied to the preview), so the resulting image is still dark.

The best way to go about doing this right is:

- Open the ScreenTransferFunction process from the process menu (don't use the icons on the toolbar).

- Now click the 'radioactive' icon in the process window to apply a basic STF.  (You may have to click the 'chain' icon just above in the process window to unlink the channels if you don't have good colour balance, or leave them linked if you do).

- You should now have your image showing with a suitable STF.

- Next open the HistogramTransformation process and start the real-time preview.

- Drag the blue triangle from the ScreenTransferFunction process window to the bottom bar of the HistogramTransformation process.  This will transfer the STF parameters to the HT process and give you a reasonable starting point for doing the stretch.

- A this point the preview window will white out or be massively over-stretched, because you have double-applied the stretch (once from the active STF and once from the HT preview).

- You now just need to de-activate the STF - close the STF process and if necessary click the icon next to the radiation icon on the toolbar to clear the active STF.

- You should find the preview now shows a similar result to what you had when you first applied the STF, i.e. a good starting stretch.

- Now tweak the HT process as you wish to get a better stretch.

- Finally drag the blue triangle from the HT process to the image window to apply the stretch.

- Save the image and when you re-open it later, you should find it has the stretch applied as you'd expect.

Hope this helps.

[RetroArchangel]

I suspect that you already had a screen transfer function (STF) active before you started the histogram transformation process.  Once you start the real-time preview of the histogram transformation, any active STF is applied to the preview in addition to changes you make to the histogram. When you apply the histogram transformation to the image (by dragging the blue triangle to the image), the same thing happens, i.e. the image is modified with the stretched histogram, but it is still displayed with the active STF as well.

Now when you save the image and re-open it later, you no longer have an active STF applied so you only see the changes from the histogram transformation (which will have been very small, since you were fooled by the STF being applied to the preview), so the resulting image is still dark.

The best way to go about doing this right is:

- Open the ScreenTransferFunction process from the process menu (don't use the icons on the toolbar).

- Now click the 'radioactive' icon in the process window to apply a basic STF.  (You may have to click the 'chain' icon just above in the process window to unlink the channels if you don't have good colour balance, or leave them linked if you do).

- You should now have your image showing with a suitable STF.

- Next open the HistogramTransformation process and start the real-time preview.

- Drag the blue triangle from the ScreenTransferFunction process window to the bottom bar of the HistogramTransformation process.  This will transfer the STF parameters to the HT process and give you a reasonable starting point for doing the stretch.

- A this point the preview window will white out or be massively over-stretched, because you have double-applied the stretch (once from the active STF and once from the HT preview).

- You now just need to de-activate the STF - close the STF process and if necessary click the icon next to the radiation icon on the toolbar to clear the active STF.

- You should find the preview now shows a similar result to what you had when you first applied the STF, i.e. a good starting stretch.

- Now tweak the HT process as you wish to get a better stretch.

- Finally drag the blue triangle from the HT process to the image window to apply the stretch.

- Save the image and when you re-open it later, you should find it has the stretch applied as you'd expect.

Hope this helps.

Thanks Ian - you are a star!

That works fine. It all makes sense.

Andy

[ollypenrice]

Ah yes, the image must be linear to start with. Good thinking from Ian.

Olly

[harry page]

Hi

You have not been eating your greens

www.harrysastroshed.com

I will bore you to death , but I might be of help

Harry

[RetroArchangel]

Hi

You have not been eating your greens

www.harrysastroshed.com

I will bore you to death , but I might be of help

Harry

Hi Harry, it was your videos that made me get PixInsight originally! Do you get paid a commission?  

I've used Photoshop professionally for years and other, non-Adobe, graphic packages sometimes seem a little strange. That said - I love PixInsight.

Andy

[harry page]

Hi

No commission   , just the joy of being told I am a strange bloke because I use Pixinsight

This vid http://www.harrysastroshed.com/scfvid.html  I believe does detail the STF and how to save images    Inc don't forget to turn the STF off

If you need more help , please ask

Harry

[RetroArchangel]

If you need more help , please ask

Thanks Harry - I will no doubt be taking you up on your offer at some point.

Andy