Re: image opacity/image overlaying?

*To*: mathgroup at smc.vnet.net*Subject*: [mg80376] Re: image opacity/image overlaying?*From*: AV <akvelu at gmail.com>*Date*: Mon, 20 Aug 2007 03:41:27 -0400 (EDT)*References*: <f9p5ut$rm2$1@smc.vnet.net><f9s2gk$9gg$1@smc.vnet.net>

Thanks alot for the reply, Your suggestion led me along the right direction and I got the effect I was looking for. I didn't realize that the Raster function, which the Import function returns, returns a graphics primitive which can be combined with other primitives unlike most of the other plotting functions. I ended up using the following to plot an overlay image over a reference image, with a variable overlay threshold and alpha value - here set to threshold 0.25 in a normalized image and alpha to 0.75. Show[{ Graphics[Raster[refimage,ColorFunction -> "GrayTones"]], Graphics[Raster[overlayimage, Automatic, {Min[overlayimage],Max[overlayimage]},ColorFunction ->(OverlayColor[#, 0.25,0.75]&)]] }]; With the following color function to allow thresholding of the overlay image. OverlayColor[ z_ ,threshold_,alpha_] := If[z > (0.5-threshold) && z < (0.5+threshold), Directive[Opacity[0],RGBColor[0,0,0]], Directive[Opacity[alpha],ColorData["TemperatureMap"][z]]]; Thanks again. AV On Aug 14, 6:09 am, "Mariusz Jankowski" <mjankow... at usm.maine.edu> wrote: > This doesn't use ArrayPlot, but works for 2D image arrays. Given two images, > for example, > > img1 = Import[ > "http://www.ee.usm.maine.edu/courses/ele489/data/cameraman.tif"; ] ; > > img2 = Import[ > "http://www.ee.usm.maine.edu/courses/ele489/data/face.tif"; ] ; > > then this gives the desired result > > Show[{img1, Graphics[{Opacity[0.5], img2[[1]]}] }] > > Bye, Mariusz > > >>> On 8/13/2007 at 4:49 AM, in message <f9p5ut$rm... at smc.vnet.net>, > AV<akv... at gmail.com> wrote: > > Is there a way of overlaying a partially transparent 2D image array on > > another 2D image array using ArrayPlot or ListDensityPlot? I am > > currently using a workaround by making an array of transparent points > > and showing this on top of a ListDensityPlot graphics but I wanted to > > check if there was a better way since this is very slow. > > > AV