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Saturation And Value Saturation And Value Modulation: A New Method Modulation: A New Method For Integrating Colour And For Integrating Colour And

Grey-Scale ImageryGrey-Scale Imagery

David Viljoen & Jeff HarrisGeological Survey of Canada

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OverviewOverview

• Why integrate colour and grey-scale data?

• Conventional methods and problems.

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

• Geoscience examples.

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Integrating Colour & Grey-scale imageryIntegrating Colour & Grey-scale imagery

Enhancing the visualizationof a dataset.

DEM with shaded relief of DEM for Mt. Logan

}

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Integrating Colour & Grey-scale imageryIntegrating Colour & Grey-scale imagery

Visualizing the relationshipsbetween two datasets.

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

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Layer transparencyLayer transparency20%

40%

60%

80%

80%

60%

40%

20%

Transparency of Colour

(Colour over shaded relief)

Transparency of shaded relief

(Shaded relief over colour)

Layer transparency control in ArcMap

Result is independentof layer order

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Red-Green-Blue coordinatesRed-Green-Blue coordinates

RGB used to define colours in computers and image files.

Integrating colour and greyscale imagery involves manipulation of coloursin RGB & HSV coordinate spaces.

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Hue–Sat–Value coordinatesHue–Sat–Value coordinates

Hue

ValueValue

V = 100

S = 1000º

120º

240º 0

100

0

100

0º 359º

SaturationSaturationHueHue

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Conventional Value ReplacementConventional Value Replacement

R

G

B

HH

SS

VV

R

G

B

RGB2HSV HSV2RGB

STOP

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Problems with Value ReplacementProblems 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)

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Problems with Value ReplacementProblems with Value Replacement

1. Pixel colour is differentiated on Value

R,G,B H,S,V

0,110,0 120,99,43

0,188,0 120,99,74

0,253,0 120,99,99

ReplaceV with pixelvalues from shaded relief

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Problems with Value ReplacementProblems with Value Replacement

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

… to replace the Values ofcolours with low saturation …

Using Values fromgrey-scale image …

… results in poorimage integration.

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Conventional RGB ModulationConventional RGB Modulation

R

G

B

R’

G’

B’

Multiply

Multiply

Multiply

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Problem with RGB ModulationProblem 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.

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Inspiration for SatValModInspiration for SatValMod

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SatValMod ConceptSatValMod ConceptLower Saturation

CutoffLower Value

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SatValMod MultipliersSatValMod MultipliersLower Saturation

Lower Value Cutoff

Value multiplier

Saturation multiplier

Shade value

Mul

tiplie

r

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SatValMod DetailSatValMod Detail

HH

SS

VV

R

G

B

*

* =

=

Pixel value in grey-scale imagedetermines multiplier

SmSm

VmVm

HSV2RGB

Multipliers

0.75

1.00

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SatValMod in ArcGISSatValMod in ArcGIS

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

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SatValMod Colour Raster OptionsSatValMod Colour Raster Options

CLR filepixel valueand RGB’s

RGB

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

RGB

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SatValMod ParametersSatValMod Parameters

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SatValMod parameters (CutOff)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).

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SatValMod parameters (Vmin)SatValMod parameters (Vmin)

Vmin = 0 Vmin = 0.3 Vmin = 0.6

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

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SatValMod parameters (Vexp)SatValMod parameters (Vexp)

Vexp = 0.3 Vexp = 1 Vexp = 3

Vexp 1 is recommended so shadows are not too extensive.

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SatValMod parameters (Smin)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.

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SatValMod parameters (Sexp)SatValMod parameters (Sexp)

Sexp = 0.3 Sexp = 1 Sexp = 3

Sexp 1 provides better results

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Geology + Shaded relief aeromag.Geology + Shaded relief aeromag.

Value replacement SatValMod RGB Modulation

SatValMod doesnot lose or corrupt original colours.

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Pan sharpeningPan sharpening

Value replacement SatValMod RGB Modulation

Colour critical?Use SatValMod.

Sharpening critical,colour unimportant?Use value replacement

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Ternary imagesTernary images

Value replacement SatValMod RGB Modulation

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

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ConclusionsConclusions

Value replacement SatValMod RGB Modulation

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.

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AvailabilityAvailability

• ArcGIS 8.x and 9.x MXD VBA • ArcMap

– ArcView or ArcInfo

• e-mail for download instructions

viljoen@nrcan.gc.ca