View source for Measure OTF of the lens-sensor system

{{Legacy}} See more about lens measurements on Elphel Blog: [https://blog.elphel.com/category/calibration/ Category:calibration]

==Software==
* Install [http://rsbweb.nih.gov/ij/ ImageJ].
* Get '''MTF_Bayer.java''' plugin from [http://elphel.git.sourceforge.net/git/gitweb.cgi?p=elphel/ImageJ-Elphel;a=tree GIT] and compile it in ImageJ.
 Note:
 1.1. Copy the source to the "Plugins" folder of the ImageJ installation
 1.2 Launch ImageJ
 1.3 Drop down menu "Plugins -> Compile and Run..."
 
 2.1 It might be useful getting the following plugins as well:
  '''JP46_Reader.java''' - converts JP46
  '''Crosstalk_Deconv.java''' - can generate simulation pattern

==Test Pattern==
<font size=4>Print the test pattern (A) or generate it (B).</font>

===A - print===
* The stripes on the paper are vertical of course. But there should be a small angle on the test image.
* Each stripe width on the test image should be not less than 32 pixels
* The minimum is 3 stripes: BWB or WBW.
{|
|[[Image:Slanted edges pattern.jpeg|thumb|400px|Test Pattern]]
|}

===B - generate===
* Get '''Crosstalk_Deconv.java''' - compile and run

* Click '''Create Color Pattern'''
* Choose ''Pattern Type''
* Set ''Nonlinearity'' to 1 (square)
* Set the stripes period (each stripe width on the test image should be not less than 32 pixels)
* '''OK''' - the plugin generates only RED, GREEN or BLUE stripes - so it will be like color filter. RED will be ok.

==Camera Settings==
{| border=1
| Gamma
| 1.0
|-
| Black Level
| 0.0
|-
| Color Saturation
| 0.0
|-
| Image Quality
| 100%
|-
| Color Sensor Mode
| Mono
|}

 Note:
 Set the Color Sensor Mode to Mono only when Color Saturation is 0.0

==ImageJ==
'''<font size=5>1.</font>''' Save the image of the test pattern.

'''<font size=5>2.</font>''' Launch ImageJ - open the saved image and launch the plugin
{|
|[[Image:Plugin interface.jpeg|thumb|600px|MTF Bayer plugin interface]]
|}
'''<font size=5>3.</font>''' Select the area of the measurement.
  Note:
  Should contain at least 2 edges - 1x Black-to-White & 1x White-to-Black but '''<font size=3>the more edges in the area of interest the better</font>'''
{|
|[[Image:Slanted edges pattern select area.jpeg|thumb|300px|Selection]]
|}

'''<font size=5>4.</font>''' '''Process''' - the MTF chart will be shown
 Note:
 Change the image type in ImageJ to 32-bit if you are getting an error: drop-down menu Image -> Type
{|
|[[Image:MTF chart example.jpeg|thumb|500px|Result chart: the MTF curves are drawn for all 4 color channels for BW and WB edge (8 as a result):
 RED - red curve, GREEN (from RGR line) - light blue curve, GREEN (from GBG line) - green curve, BLUE - blue curve]]
|}

'''<font size=5>5.</font>''' '''Show MTF text''' for spreadsheet use.

==Results==
* The higher curve the better.
* Normally the blue channel has the worst curve.