Hinode/XRT stray light correction 2015

Detail of the 2015/07/18 Ti-poly image correction.

[Analysis by image_corr_tp3.pro]

Composite image before corr. obtained 15:53:55UT.	Stray light image. obtained 16:09:21UT.

[Image 1(spot corrected)]=[Composite image(spot corrected)]-[Stray light image]
[Image 2(spot corrected)]=[Composite image(spot corrected)]-[Stray light image(spot corrected)]
[Image 3(spot corr.)]=[Composite image]-shift([Stray light image],-1,-1)
[Image 4(spot corr.)]=[Composite image(spot corr.)]-shift([Stray light image],-1,-1)

Corrected image 1.	Corrected image 2.

Corrected image 3.	Corrected image 4.

From the coalignment data base,

IDL> center_comp=[iicomp0.xcen,iicomp0.ycen]
IDL> print,center_comp
      -25.013788       21.171164
IDL> center_stray=[ii_stray.xcen,ii_stray.ycen]
IDL> print,center_stray
      -25.412954       19.968815
IDL> sft_xy=center_stray-center_comp
IDL> print,sft_xy
     -0.39916611      -1.2023487

[Image 5(spot corrected)]=[Composite image(spot corrected)]- shift_img([Stray light image],[-0.4,-1.2])

Corrected image 5.

[summary]
Image 1: spots & wood-ring best corrected, but diagonal band edges not removed. (--- the best among 5)
Image 2: white spots appeared, diagonal band edges not removed.
Image 3: white spots & enhanced dusts, diagonal band edges perfect.
Image 4: enhanced dusts, diagonal band edges perfect.
Image 5: enhanced dusts, wood-ring enhanced, diagonal band edges perfect.

S/N improvement by 4-image composite

Since 30-Jun-2015, the Ti-poly synoptics sequence is taken with 4 exposures. This is because the Ti-poly exposures should be less than 1.4 sec so that the observed signals do not exceed 2500 DN. The 2 long(1 sec) exposure images are added-up to get a defacto 2 sec exposure image. If we want deeper exposures, say, 5 sec, we need to take 5 images with 1-sec exposure.

- short :   16ms
- medium:  354ms
- long_1: 1024ms
- long_2: 1024ms

In response to these 4-image sets of Ti-poly synoptics, a special composite making procedure, MK_XRT_TPCOMP4.PRO was prepared. This procedure works :

1) PREP all 4 images (long1, long2, medium, short), normalize intensity.
2) take average of long1 and long2 and make a map of saturated pixels 
   and telemetry dropped frames.
3) replace the saturated/dropped pixels with those of medium and short 
   images'.

Comparing 3- and 4-image composites (Javascript movie)