Smartphone NIR Technical Notes

Introduction

We have adapted the Google (Nexus 5X, Nexus 5, Galaxy Nexus) and Apple (iPhone 6s, 6, 5s) smartphones for multi-spectral imaging applications (visible-to-near-infrared capability).

Promising applications include near infrared photography, vegetation analysis, assisted night vision, UV/IR authentication, biological detection, urban growth analysis, defeating camouflage, disaster assessment, etc.

Use EigenCAM app to extract and isolate multi-spectral contents. 
Top row - clustering of red, blue, index.
Mid row - green cluster, decorrelation, near infrared.
Bottom row - RGB, NDVI in colors.
 

What to expect?

The imaging sensor can see from visible-to-near-infrared (VIS-NIR) spectrum.  The spectral response graph below is representative of many typical CMOS sensors being used in current smartphones.. 
 
spectral response of Google Nexus 5x image sensor camera
 

 

NIR Sensitivity of iPhone 6 Plus Vs. Nexus 5X

The video below demonstrates spectral sensitivity of the NIR camera modules that we had modified for the iPhone 6 Plus and the Nexus 5X.  For the experiments, we used scientific grade Semrock 365nm and CVI 1050nm optical filters.
 
The results showed that Nexus 5X has a much higher spectral response in the NIR region around 1050nm.  If your application is to detect NIR fluorescence ink or dye then the Nexus 5X is a better choice.

 

Even though the Nexus 5X has better sensitivity near 365nm, it is still not suitable to use because the lens material is not made for UV 365nm imaging hence the poor focus seen in the video.  Spectrometer measurements of the lens shows highly attenuated light transmission in this UV region.

 

 

NIR Nexus 5X Built-in 850nm Illuminator

This video demonstrates night vision recording utilizing its built-in 850nm "laser autofocus" as a NIR illuminator. For close distance imaging, its built-in NIR illuminator seems sufficient.


 
 

NIR Nexus 5 with Bandpass Filter

Using a triple notch filter (pass blue, cut green, pass red) vegetation can be isolated from the background for further analysis.

 

NIR Nexus 5 OIS

Optical Image Stabilization is a mature technology that minimizes blur caused by camera shake. More recently, thanks to mobile technology evolution, it has rapidly become an essential feature across flagship smartphones. In certain circumstances, it is better to disable Optical Image Stabilization.

 

 

NIR iPhone 5s

iPhone 5s Visible-to-Near-Infrared imagery vs original visible imagery

 

 

Detect NIR Barcode Fluorescence

Although most fluorophophores operate in visible or ultraviolet parts of the spectrum, near infrared (NIR) area is a very promising for fluorescence detection and imaging.  We used the iPhone 5s to detect near infrared (NIR) fluorescent security / anti-counterfeit barcodes. 

 

 


Camera Functions Stay the Same

    Focus distance stays the same.  We do a re-calibration of the focusing, on applicable models, after the removal/replacing of the internal IR cut off filter.  Adjusting lens setting or adding focus compensating filter to recalibrate nominal focus. 

     

     
     
    You can always place an NIR cut-off filter in front of the lens to take a standard RGB color image as usual.  Or you can mount any other bandpass filters per your application.  Applications are limited only by your imaginations.



         

        What's the EigenCAM App?

        The EigenCAM app is an imaging and analysis software specifically designed for multi-spectral imaging applications to extract as much information as possible from the images.  (iOS app is coming soon).  Its intuitive graphical user interface allows users to quickly perform a host of image processing and analysis functions.

          Analyze check forgery 
          Left - RGB image.  
          Right - Reveal altered name on check.
           

           

          Remote Sensing Algorithm

          This video segment demonstrates Multispectral Image Processing algorithms.  We have developed these algorithms to run on Android and IOS platforms. Image processing can be done on captured imagery, by phone's camera, or live video. Image enhancement techniques are application specific so that visual interpretation of the result is more suitable than the original image. Over time, researchers have developed many algorithms which have shown that certain predictions can be made from the acquired imagery alone. The choice of algorithms to use depends on the goals of each individual project. With the right training and tools, multispectral imagery can be leveraged to help the naked eye see things that may not have been visible before.

           

          Flat Field Vignetting Correction

          This video segment demonstrates Flat Field Correction.  Flat field correction is a technique used to improve quality in digital imaging by correcting for variations in sensitivity across an image plane.  An example of this effect can be seen when a narrow band-pass filter is being used in conjunction with a wide angle lens.  Intensity response of a narrow band-pass filter is very sensitive with respect to the incident angle and thus causes a non-uniformity intensity response toward the edge of an image. This technique is also used to remove dust spots in images captured by a camera due to external dust particles that have found their way into the camera.

           

          Vegetation Spectral Mapping

          This video segment demonstrates Spectral Similarity Mapping.  Spectral similarity mapping in vegetation is useful for locating various types of plant over a large landscape.  Region of interest can be easily extracted to estimate the percentage of coverage area for a more effective landscape management. NDVI algorithm could be called to operate on the region of interest to investigate the soil background characteristics and variations in percent canopy cover.

           

           

          Why choose NIR smartphones and EigenCAM app?

          • Image analysis can be done via the image capturing mode or live video mode.
          • Portable and inexpensive solutions for applications such as vegetation analysis, night vision, authentication, biological detection, urban growth analysis, defeating camouflage, disaster assessment, etc.
          • Take advantage of the Android capabilities.  IOS coming soon,

               

              We can customize to your specific applications.

              Sales and Support
              info@eigenimaging.com
               
              US distributor
              James Le
              jle@tunatronics.com
              Tel. 714.588.1220
              Fax 714.668.1907