Measure OTF of the lens-sensor system

This is a legacy page. Information may not reflect the current state of the products or code. See more about lens measurements on Elphel Blog: Category:calibration

Software

• Install ImageJ.
• Get MTF_Bayer.java plugin from 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

Print the test pattern (A) or generate it (B).

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.

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

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

1. Save the image of the test pattern.

2. Launch ImageJ - open the saved image and launch the plugin

MTF Bayer plugin interface

3. Select the area of the measurement.

 Note:
 Should contain at least 2 edges - 1x Black-to-White & 1x White-to-Black but the more edges in the area of interest the better

Selection

4. 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

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

5. Show MTF text for spreadsheet use.

Results

• The higher curve the better.
• Normally the blue channel has the worst curve.