False-color elevation map --> grey scale?

Let's say I have a false-color elevation map, purple for low, then going up through blue, green, yellow, orange, red, and finally
white. Does anybody know a way to convert this into a simple grey scale height map? In other words, black = low, white = high.
Changing the image to greyscale is not sufficient, as the green and yellow areas stand out as higher than the red, due to their
higher luma values. If I have a rectangle with the colors in order, can I analyze that and apply it as a gradient to the rest of
the image? I ask this because most 3D programs I know only accept greyscale height maps as a displacement terrain map, and most
height maps I'm able to get use this false-color format instead...

"Darrel Hoffman" ...

Let's say I have a false-color elevation map, purple for low, then going up through blue, green, yellow, orange, red, and finally
white. Does anybody know a way to convert this into a simple grey scale height map? In other words, black = low, white = high.
Changing the image to greyscale is not sufficient, as the green and yellow areas stand out as higher than the red, due to their
higher luma values. If I have a rectangle with the colors in order, can I analyze that and apply it as a gradient to the rest of
the image? I ask this because most 3D programs I know only accept greyscale height maps as a displacement terrain map, and most
height maps I'm able to get use this false-color format instead...

Darrel, I use greyscale heightmaps quite a bit for 3-D (such as Bryce) and implied 3-D (such as KPT 5 Shapeshifter). When I want to control the tone of a color conversion, I go to Hue and Saturation (command U) and desaturate individual colors RYGCBM and either darken or lighten to suit my needs.

The following terrain surrounding an imported alpha channel-masked photo of Kai Krause was done in the manner described above in Bryce 4:

http://www.amenfoto.com/gallery/metagallery/kaios.html

cheers,
Adrian

From: "Darrel Hoffman" asked

.....

Probably the easiest way is to extract the hue channel from your map.

It sounds

as though the colors have been selected in order of hue, as is fairly

common.

Yeah, that sounds about right - but how do you DO it? I consider myself reasonably advanced in both Photoshop and 3D Max, but I
know of no direct way to convert the RGB channels to HSB, or tell Max to read the hue channel instead of the brightness for height calculations. It seems to me there should be a utility or plugin designed for this specific purpose, as cartographers for whatever reason tend to favor the false-color format, while almost all 3D software I know requires greyscale. Is there some way to make
these two types talk to eachother?

Some earlier versions of Photoshop for the Mac (I think 4.0 and 5.0) shipped with a plugin on the CD that would convert an RGB image to HSI. There is also a routine that can do that or just extract the hue channel from an image in the Image Processing Tool Kit from www.ReindeerGraphics.com

Yeah, that sounds about right - but how do you DO it? I consider myself reasonably advanced in both Photoshop and 3D Max, but I
know of no direct way to convert the RGB channels to HSB, or tell Max to read the hue channel instead of the brightness for height calculations. It seems to me there should be a utility or plugin designed for this specific purpose, as cartographers for whatever reason tend to favor the false-color format, while almost all 3D software I know requires greyscale. Is there some way to make
these two types talk to eachother?

Some earlier versions of Photoshop for the Mac (I think 4.0 and 5.0) shipped with a plugin on the CD that would convert an RGB image to HSI. There is also a routine that can do that or just extract the hue channel from an image in the Image Processing Tool Kit from www.ReindeerGraphics.com

Okay, looked at that. I just don't understand why this should be such a complicated thing to do. Extract the hue channel to a
grey-scale image. Simple as that. It shouldn't cost me $250 to do such a basic operation (Or would I need their $800 package for
this?!?). Are you sure there isn't a cheaper (or dare I ask - free) solution to this problem? This seems like something that
anyone with a little coding skill and 5 minutes of spare time should be able to come up with fairly easily. I'd be very surprised
if there wasn't some freeware utility for just this purpose out there...

From: "Darrel Hoffman"

.......snip....

Okay, looked at that. I just don't understand why this should be such a complicated thing to do. Extract the hue channel to a
grey-scale image. Simple as that. It shouldn't cost me $250 to do such a basic operation (Or would I need their $800 package for this?!?). Are you sure there isn't a cheaper (or dare I ask - free) solution to this problem? This seems like something that
anyone with a little coding skill and 5 minutes of spare time should be able to come up with fairly easily. I'd be very surprised if there wasn't some freeware utility for just this purpose out there...

I told you that there was a free one once distributed with PShop, so if you want to track that down (and you have a Mac) go for it. Sure, someone with the appropriate coding skills, programming tools, experience with photoshop plugins etc. can write what you want. And maybe someone will, and even give it to you free. The $250 tool kit package includes a lot more than that one function, but as far as I know it is the only available routine at this time.

I told you that there was a free one once distributed with PShop, so if you want to track that down (and you have a Mac) go for it.

Do you remember the name of this plugin? Are you referring to the Chromagraphics plugin by any chance? (I've got a Mac version 5
CD that I just checked.) There is a demo plugin, but it's handicapped, in that it won't allow you to save, which essentially
renders it nearly useless. (I could take screen-Theoretically, I could register the software and get the full unlocked version,
except that the company appears to no longer exist. (And even if they did, I'd imagine that their pricing wouldn't be much better
than the ReindeerGraphics product.) Or is it something else entirely?

(Not wanting to reinstall Photoshop 5 unless absolutely necessary. I'm not even sure it will work under OSX...)

(Wow, that got screwed up. Let's try that again, shall we?)

I told you that there was a free one once distributed with PShop, so if you want to track that down (and you have a Mac) go for it.

Do you remember the name of this plugin? Are you referring to the Chromagraphics plugin by any chance? (I've got a Mac version 5
CD that I just checked.) There is a demo plugin, but it's handicapped, in that it won't allow you to save, which essentially
renders it nearly useless. (I could take screen-captures and paste the image together in sections, but that seems wrong,
somehow...) Theoretically, I could register the software and get the full unlocked version, except that the company appears to no
longer exist. (And even if they did, I'd imagine that their pricing wouldn't be much better than the ReindeerGraphics product.) Or
is it something else entirely?

(Not wanting to reinstall Photoshop 5 unless absolutely necessary. I'm not even sure it will work under OSX...)

From: "Darrel Hoffman"
Date: Tue, Aug 5, 2003 11:57 AM
Message-id: <bgokhq$d87$>

Do you remember the name of this plugin? Are you referring to the

Chromagraphics

plugin by any chance?

My recollection is that it went by the name of RGB<>HSB or something close to that. It was NOT third party but supplied by Adobe.

(Not wanting to reinstall Photoshop 5 unless absolutely necessary. I'm not even sure it will work under OSX

It actually will, in Classic. But plugins written for OS9 compatibility will not run native under OSX