Raster Function Template for 8-bit raster with 0 and 1 values

Heidi_Kristenson — Fri, 14 Oct 2022 20:14:03 GMT

I can't seem to generate an appropriate raster function template to visualize an 8-bit raster with a Min-Max stretch from 0 to 1 with a color ramp.

I have a collection of 8-bit unsigned rasters that contain only 0 and 1 values (and NoData) that are destined for an image service. I want to generate a raster function template to symbolize the rasters so that 0 values are a 50% transparent white and 1 values are blue. This has proven unbelievably difficult, even though it's very easy to apply such a symbology directly in ArcGIS Pro.

What I want to replicate is this fairly simple Stretch setting:

There's a Min-Max stretch applied, from 0 to 1 (using Custom stats). I've generated a custom discrete multipart color scheme where the low values (encompassing 0) have a 50% transparent white applied, and high values (encompassing 1) are blue.

If you simply save this symbology as a Raster Function Template, it saves as a "Rendered Raster" function. This then displays as an RGB image, with no transparency on the white pixels, rather than a stretched raster with values from 0 to 1.

There are no settings listed in the parameters; it's completely opaque what sort of rendering is being applied to this raster. The legend simply displays the RGB bands, rather than a color bar with the stretched Min-Max values.

My first thought was to just build a raster function template using first a Stretch function followed by a Colormap function. I tested each component, and if I just apply the Stretch function I can get the basic behavior I want, just in black and white:

It seems like I should be able to simply add the Colormap function to apply my custom color scheme, and the black-to-white color ramp would be replaced with my transparent white and blue color ramp. But when I do that, the scaling reverts to 0 to 255. As such, both 0 and 1 are in the transparent white region of the color ramp.

It also changes the legend display to a discrete display, where every number from 0 to 255 has a color patch, rather than just displaying the stretch colorbar. Incidentally, it only displays the transparent white from 0-19, the blue from 20-39, then displays a range of green to red colors for the remaining 40-255 (not sure what's driving that, seeing as I only set 2 colors in the multipart ramp settings).

I tried adjusting the color ramp so that 0 and 1 would have different colors, but it's pretty tricky because they're so close together in the scope of 0 to 255. And even so, the legend is unwieldy. I'd like to just see the colorbar like I do when I manually set the symbology.

I tried switching the order of the colorbar and stretch functions, but that wasn't helpful.

I also tried exporting a Classified Symbology setup as a RFT, but again, it just saves that symbology as a Rendered Raster setting, so it's just an RGB output, with no transparency capabilities or legend.

Any ideas?

Re: Raster Function Template for 8-bit raster with 0 and 1 values

Heidi_Kristenson — Fri, 14 Oct 2022 20:13:05 GMT

I should mention that I'm on ArcGIS Pro 2.8.3

Re: Raster Function Template for 8-bit raster with 0 and 1 values

Heidi_Kristenson — Fri, 14 Oct 2022 21:57:53 GMT

I've made a bit of progress by using a custom .clr file:

I just generated a text file with a line each for the two values in my raster, and defined a color for each one.

This is the closest I've come to what I'm looking for, but it doesn't seem to support transparency. Any suggestions on that front would be welcome.

I also would love to be able to rename the values that display next to the legend (i.e. display "Water" instead of "1"), which can't be designated within the .clr file.

Re: Raster Function Template for 8-bit raster with 0 and 1 values

LindaWilliams1 — Fri, 14 Oct 2022 22:43:42 GMT

Will the colormap import accept an alpha value of .5 (1 0 169 230 .5) for the transparency?

Re: Raster Function Template for 8-bit raster with 0 and 1 values

Heidi_Kristenson — Fri, 14 Oct 2022 23:00:00 GMT

The Colormap function doesn't seem to apply transparencies @LindaWilliams1.

I tried adding transparency values at the end of my .clr file entries, but it didn't make any difference in the output; everything was still fully opaque.

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Raster Function Template for 8-bit raster with 0 and 1 values

Re: Raster Function Template for 8-bit raster with 0 and 1 values

Re: Raster Function Template for 8-bit raster with 0 and 1 values

Re: Raster Function Template for 8-bit raster with 0 and 1 values

Re: Raster Function Template for 8-bit raster with 0 and 1 values