Author Topic: Converting image to non linear.  (Read 193 times)

Offline tomb18

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Converting image to non linear.
« on: 2019 October 11 09:33:18 »
I have a rather strange issue with an rgb Ha image and I dont know what to do about it.
I have a red green and blue and when I combine them, the resulting image is perfect without using the screen transfer function. I can save this as a tiff or jpeg, and then it is clearly linear without anything showing since it was not stretched.
I tried applying a stretch with histogram transformation and the preview is exactly as the image looks but the minute I try and adjust it, I lose the perfect image I had and I cannot seem to get back to it! Is there a way to just keep what I have and save it so that it keeps whatever parameters make it look so good?
Thanks, Tom

Offline dave_galera

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Re: Converting image to non linear.
« Reply #1 on: 2019 October 11 10:15:06 »
Hi Tom,

Yes I have had this effect, try clicking the STF reset and then re-apply the Auto stretch.

To convert to non-linear copy STF instance to HistogramTransformation, reset STF, apply HistogramTransformation.
Dave

Offline niteman1946

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Re: Converting image to non linear.
« Reply #2 on: 2019 October 11 11:11:06 »
To follow up on Dave's comments;

1.  Bring up linear image.  It should display fully stretched.
2.  Bring up ScreenTransferFunction and HistogramTransformation.
3.  Make sure upper bar of image is blue (active).
4.  Drag blue triangle from STF to bottom gray bar of HT (same location as the HT's blue triangle).
5.  Drag blue triangle from HT to image.  This will produce a double stretch and image will likely go white.
6.  Click on the White TV image icon on upper right of the screen.  This icon is just to left of similar icon marked "24".

Image should return to what you want and should now be fully stretched and able to save as a usable image.

Sorry if I've misread your comments, and please ignore if you know all of this.

Good luck,
Mark

Offline tomb18

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Re: Converting image to non linear.
« Reply #3 on: 2019 October 11 14:15:15 »
Hi,
I managed to get this OK but step 5 doesn't do a double stretch.
What I finally end up with is basically starting from scratch.  Still not as nice as the auto stretch was.
Anyways I can now save a jpg for example and it is correct.  So what does the enable / disable screen transfer function do? I guess it saves the information in the file?
Tom

Offline ngc1535

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Re: Converting image to non linear.
« Reply #4 on: 2019 October 11 14:49:04 »
Hi Tom,
I sent you a private message...it might help.
Of course... it might not! (you can report back)
lol
-adam

Offline jkmorse

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Re: Converting image to non linear.
« Reply #5 on: 2019 October 14 07:39:42 »
Tom,

It might just look like a double stretch because you haven't turned off STF.  Before or after stretching (it really doesn't matter) simply shut off STF and everything should look fine.

Jim
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