STF Autostretch not being saved to a Tiff

JohnDrummond

Member
Nov 22, 2013
13
0
Hi. A real newbie here.

I'm wanting to use 'STF Autostretch' to look at test images - and save them as Tiffs. When I do the STF Autostretch and then attempt to save it as a Tiff a warning box pops up stating, 'The Tiff format does not support some existing data in this image. The specified data will not be written to the output file'. I ignore this and try to save it anhway. When I open the saved Tiff it's all black the the STF Autostretch wasn't applied.

Any ideas on how to do the STF Autostretch and then save the stretched result as a Tiff?

Regards
John D, NZ
 

pfile

PTeam Member
Nov 23, 2009
5,625
105
STF stands for 'screen transfer function' and that's what it does - applies a stretch to the image data in memory but does not actually modify the data. hence when you save the file with an STF applied, the pixels do not change. the warning comes about because the new PI-centric file format called XISF can remember the screen stretch and re-apply it when you re-open the file. since TIFF can't do this, PI is warning you that you'll lose the STF information (as well as other stuff that XISF can support, like FITS keywords.)

if you want to change the data and save it out to a file, you'll need to use the HistogramTransformation process. if you like the STF that was auto-computed, you can drag the triangle from STF to the bar containing the triangle in HistorgramTransformation, then drag the triangle from HT to the image. at that point the image will turn completely white as there is a double stretch applied. at this point you should turn off the STF on the image. it should return to the way it looked with the STF applied. then if you save the file to any format, the data on disk will be stretched and visible to any other program.

rob
 

JohnDrummond

Member
Nov 22, 2013
13
0
Thanks Rob. I've been overseas and am now readdressing this issue.

I can do some of what you suggest but can't figure out how to turn off the STF on the image once I've dragged its blue triangle into the Histogram bar - and then dragged the blue triangle onto the image. You're right, it all turns white. BTW, I want to invert the image too.

Many thanks
John D, NZ
 

pfile

PTeam Member
Nov 23, 2009
5,625
105
yes - and there are also keyboard shortcuts. on the mac it's control-S to toggle the STF. not sure of the other platforms, but if you right click on the image and go down to the "Screen Transfer Function" pop-out menu, you should see the keyboard shortcuts.

rob
 

JohnDrummond

Member
Nov 22, 2013
13
0
Awesome, thanks. I seem to have success now. Many thanks for your help guys.

BTW, I'm up to Chapter 7 (Batch Processing) in Warren Keller's 'Inside PixInsight'. Long way to go - since I'm doing each instruction on my screen as I read it. Great book!

Regards and thanks once again
John D, NZ