VIEWS: 1 PAGES: 30 POSTED ON: 2/16/2012
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 7/30 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 26/30 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 email@example.com 30/30
"Saturation And Value Modulation A New Method For Integrating "