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Saturation And Value Modulation A New Method For Integrating

VIEWS: 1 PAGES: 30

									   Saturation And Value
 Modulation: A New Method
For Integrating Colour And
    Grey-Scale Imagery
    David Viljoen & Jeff Harris
        Geological Survey of Canada




                                      1/30
                         Overview

• Why integrate colour and grey-scale data?

• Conventional methods and problems.

• Saturation-Value-Modulation concept &
  SatValMod ArcGIS implementation.

• Geoscience examples.

                                              2/30
Integrating Colour & Grey-scale imagery

                 Enhancing the visualization
                 of a dataset.




            }      DEM
                   with shaded relief of DEM
                   for Mt. Logan


                                    3/30
Integrating Colour & Grey-scale imagery
                  Visualizing the relationships
                  between two datasets.




            }       K-Th-U (RGB)
                    Gamma ray spectrometer
                    with Landsat TM 7

                                  4/30
                                 Layer transparency
                                 20%



                                        40%
                                                     Result is independent
                                                     of layer order

                                                    60%
80%



      60%
                                                                       80%




                                  40%




            Layer transparency
            control in ArcMap                 20%


                                                          5/30
Red-Green-Blue coordinates

           RGB used to define colours
           in computers and image files.

           Integrating colour and grey
           scale imagery involves
           manipulation of colours
           in RGB & HSV coordinate
           spaces.




                             6/30
              Hue–Sat–Value coordinates
                                  Saturation
        Hue                         V = 100
                       100
 120º


                        0




                  0º
                                    Value
                                    S = 100
                       100




240º                    0
                             0º                       359º
                                     Hue




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Conventional Value Replacement


R             H                    R


G   RGB2HSV   S          HSV2RGB   G


B             V   STOP
                                   B




                                       8/30
         Problems with Value Replacement


•    Loss/corruption of colour where:
    1. Pixel colour is differentiated on Value (HSV)

    2. Pixel colour has low saturation (achromatic
       axis of RGB cube)




                                            9/30
    Problems with Value Replacement
1. Pixel colour is differentiated on Value

                       R,G,B      H,S,V           Replace
                       0,110,0   120,99,43        V with pixel
                                                  values from
                       0,188,0   120,99,74        shaded relief
                       0,253,0   120,99,99




                                          10/30
              Problems with Value Replacement

2. Pixel colour has low saturation
   (achromatic axis of RGB cube)

Using Values from    … to replace the Values of      … results in poor
grey-scale image …   colours with low saturation …   image integration.




                                                           11/30
Conventional RGB Modulation


    R    Multiply   R’


    G    Multiply   G’


    B    Multiply   B’




                         12/30
        Problem with RGB Modulation
Overwhelming majority of pixels in the output
raster will have a darker colour than original.
                         Better than value replacement.

                         Colours are not “lost” but
                         what happened to the yellow.




                                          13/30
Inspiration for SatValMod




                      14/30
                 SatValMod Concept
              Lower Saturation




Lower Value
                     Cutoff
                                     15/30
                           SatValMod Multipliers
                           Lower Saturation




                           Saturation multiplier
Multiplier




                            Value multiplier




                    Shade value


             Lower Value
                                    Cutoff
                                                   16/30
                            SatValMod Detail

H                                               R
           Multipliers
           1.00

S   *                        =   Sm   HSV2RGB   G

            0.75

V   *                        =   Vm             B


    Pixel value in
    grey-scale image
    determines multiplier



                                                    17/30
SatValMod in ArcGIS


       SatValMod written in VBA
       Runs in ArcGIS 8.x or 9.x
       (ArcMap – ArcView or ArcInfo)




                        18/30
    SatValMod Colour Raster Options




                                   R                       R
 CLR file                           G                       G
pixel value                          B
and RGB’s
                                                             B



                   8-bit image planes        3 separate
                                           8-bit raster files




                                         19/30
SatValMod Parameters




                   20/30
                  SatValMod parameters (CutOff)




      CutOff = 255                           CutOff = 180                          CutOff = 128
CutOff should be the maxima of the shade raster histogram. For shaded relief images, this is sin(Altitude).

                                                                                     21/30
           SatValMod parameters (Vmin)




Vmin = 0                        Vmin = 0.3                           Vmin = 0.6
             Vmin > 0 is best so shadows are not completely black.

                                                                     22/30
             SatValMod parameters (Vexp)




Vexp = 0.3                          Vexp = 1                             Vexp = 3
             Vexp  1 is recommended so shadows are not too extensive.

                                                                         23/30
           SatValMod parameters (Smin)




Smin = 0                            Smin = 0.3                            Smin = 0.6
Smin < 0.4 is recommended. Higher values do not provide enough decrease in saturation.

                                                                           24/30
             SatValMod parameters (Sexp)




Sexp = 0.3                   Sexp = 1                Sexp = 3
                  Sexp  1 provides better results

                                                     25/30
            Geology + Shaded relief aeromag.
SatValMod does
not lose or corrupt
original colours.



  Value replacement   SatValMod    RGB Modulation




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                        Pan sharpening
Colour critical?
Use SatValMod.

Sharpening critical,
colour unimportant?
Use value replacement

Value replacement        SatValMod   RGB Modulation




                                          27/30
                                Ternary images




Value replacement                   SatValMod                     RGB Modulation




            U-Th-K RGB composite image integrated with shaded relief DEM

                                                                           28/30
                                Conclusions
 SatValMod provides better
  integration of colour and
  grey-scale imagery
  compared to many
  traditional methods.
 Colour is more accurate.
 SVM Parameters provide
  flexibility on integration.

      Value replacement          SatValMod    RGB Modulation




                                                  29/30
                          Availability
• ArcGIS 8.x and 9.x MXD
  VBA
• ArcMap
   – ArcView or ArcInfo


• e-mail for download
  instructions

      viljoen@nrcan.gc.ca




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