# "Colour mapping" - help needed to create RGB value
**URL:** https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364
**Category:** General
**Created:** [26 September 2020 01:08 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364 "2020-09-26T01:08:19Z")
**Posts on this page:** 16
**Page:** 1
### Author:  [@Trying\_to\_learn](https://discourse.nodered.org/u/Trying_to_learn)
#### Post date: [26 September 2020 01:08 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364/1 "2020-09-26T01:08:19Z")
# _Today's quest_
I receive temperature values. 30 - 75 (example)
I want to display that with a RGB LED.
Say 30 - 36 --\> blue. Green starts to creep in then.
36 - 40 --\> Blue fades out and becomes green. Towards the 40, red starts to come in.
40 - 75 --\> Green fades out and it becomes only red.
Ok, vague. (I'm good at that. 😉 )
But can it be done _nicely_?
Or do I have to generate the separate R, G, and B values and create the colour?
(
What is the command to _map_ one range to another again?
So I want to map 1 - 32 against 0 - 256.
just for an example using easy fit numbers.
)
I have kind of got something working but it isn't exact.
External node required:
`node-red-contrib-fan`
(A favourite of mine sorry)
The problem is the `green` value gets too whacky in the value it returns at the higher end.
```auto
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":820,"y":2300,"wires":[["c32946c3.21286"],["5094de08.eec4d8"]]},{"id":"a868e355.1e44d8","type":"switch","z":"2a10ff07.234f98","name":"","property":"payload","propertyType":"msg","rules":[{"t":"gte","v":"0","vt":"num"},{"t":"else"}],"checkall":"true","repair":false,"outputs":2,"x":820,"y":2380,"wires":[["141f69ec.ab5136"],["5f1d37b2.7677f8"]]},{"id":"28facc23.30dfb4","type":"change","z":"2a10ff07.234f98","name":"0","rules":[{"t":"set","p":"payload","pt":"msg","to":"0","tot":"num"}],"action":"","property":"","from":"","to":"","reg":false,"x":950,"y":2240,"wires":[["37f77004.edfbb"]]},{"id":"5094de08.eec4d8","type":"change","z":"2a10ff07.234f98","name":"0","rules":[{"t":"set","p":"payload","pt":"msg","to":"0","tot":"num"}],"action":"","property":"","from":"","to":"","reg":false,"x":950,"y":2320,"wires":[["c32946c3.21286"]]},{"id":"5f1d37b2.7677f8","type":"change","z":"2a10ff07.234f98","name":"0","rules":[{"t":"set","p":"payload","pt":"msg","to":"0","tot":"num"}],"action":"","property":"","from":"","to":"","reg":false,"x":950,"y":2400,"wires":[["141f69ec.ab5136"]]}]
```
---
### Author:  [@Colin](https://discourse.nodered.org/u/Colin)
#### Post date: [26 September 2020 06:04 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364/2 "2020-09-26T06:04:07Z")
> [@Trying\_to\_learn](#):
>
> map 1 - 32 against 0 - 256
The Range node will do that. Possibly use three, one for each colour, with appropriate input ranges.
---
### Author:  [@Trying\_to\_learn](https://discourse.nodered.org/u/Trying_to_learn)
#### Post date: [26 September 2020 06:14 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364/3 "2020-09-26T06:14:39Z")
Thanks Colin.
What is now biting me is that it isn't _that simple_. ☹_(When is it?)_
Did you look at the flow?
I kind of _cheated_ with the `blue` in that it was reversed with the value.
eg:
So: blue 0 - 5 would give an output from 255 - 0 (Darkening as the value went up)
red was simple
Ok, I'll start again:
Say the input range is 30 --\> 75
`blue` is mapped from 31 -\> 44 getting darker as the number gets bigger.
`red` is mapped from 60 -\> 75 getting brighter as the number gets bigger.
(Easy.)
`green` is where it all fell apart.
It is mapped from 40 -\> 64.
But it is a hump/bell curve and not like the other two.
So, starting at (say) 30: It would be blue.
As it rises, the `blue` would reduce and the `green` would start to increase.
Continuing, the `blue` would be `0` and `green` would be `255` at about.... 52 (?)
Then above 52 the `green` would then start to fall off again and the `red` would start to come into the _picture_.
The machine using it is now off-line.
But from the flow I posted, the `switch` nodes weren't helping and doing some strange things sometimes with the `green` part.
It worked better than the original bit where it was simply a monochrome LED who's intensity varied with the value.
Simple, but a bit non-intuitive.
But thanks for the reply.
Any thoughts on what / how I can get the `green` part _working_?
Here is the new flow I have which kinda works.
But it is a _dog's breakfast_ in how it gets things done.
```auto
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out","z":"3caae529.4226aa","name":"","links":["edf7b494.05e39"],"x":2495,"y":1580,"wires":[]},{"id":"f045c230.d9b2f8","type":"template","z":"3caae529.4226aa","name":"","field":"payload","fieldType":"msg","format":"handlebars","syntax":"mustache","template":"{{Temperature_LED}},{{red}},{{green}},{{blue}}","output":"str","x":2370,"y":1580,"wires":[["f70a880e.1468a","93b63ed3.cf2b7"]]},{"id":"f70a880e.1468a","type":"debug","z":"3caae529.4226aa","name":"RGB","active":false,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","x":2490,"y":1400,"wires":[]},{"id":"7ef4c417.22ac3c","type":"debug","z":"3caae529.4226aa","name":"","active":false,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","x":2250,"y":1440,"wires":[]},{"id":"9626dd05.4b254","type":"function","z":"3caae529.4226aa","name":"","func":"//node.warn(msg);\n\n//if (msg.red !== null)\n//{\n// context.set(\"RED\",msg.red);\n// node.warn(\"Red set\");\n//} else\n//if (msg.green !== null)\n//{\n// context.set(\"GREEN\",msg.green);\n// node.warn(\"Green set\");\n//} else\n//if (msg.blue !== null)\n//{\n// context.set(\"BLUE\",msg.blue);\n// node.warn(\"Blue set\");\n//}\nif (flow.get(\"RED\") !== null && flow.get(\"GREEN\") !== null && flow.get(\"BLUE\") !== null)\n{\n msg = {\n red:flow.get(\"RED\"),\n green:flow.get(\"GREEN\"),\n blue:flow.get(\"BLUE\"),\n Temperature_LED:flow.get(\"Temperature_LED\")\n }\n flow.set(\"RED\",null);\n flow.set(\"GREEN\",null);\n flow.set(\"BLUE\",null);\n return msg;\n}\n","outputs":1,"noerr":0,"x":2220,"y":1580,"wires":[["7ef4c417.22ac3c","f045c230.d9b2f8"]]},{"id":"75a4a4a2.d1f824","type":"delay","z":"3caae529.4226aa","name":"","pauseType":"delay","timeout":"1","timeoutUnits":"seconds","rate":"1","nbRateUnits":"1","rateUnits":"second","randomFirst":"1","randomLast":"5","randomUnits":"seconds","drop":false,"x":2050,"y":1580,"wires":[["9626dd05.4b254"]]}]
```
---
### Author:  [@Colin](https://discourse.nodered.org/u/Colin)
#### Post date: [26 September 2020 07:55 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364/4 "2020-09-26T07:55:01Z")
If you want one of them to go up then down again then for that colour you could use a Switch node to split the input above or below 52 to two outputs. Then use a Range node in each output configured to convert the ranges 40:52 to 0:255 and 52:64 to 255:0, or whatever the numbers are. Make sure you set all the Range nodes to Scale and Limit mode so they will clamp at 0:255.
---
### Author:  [@Trying\_to\_learn](https://discourse.nodered.org/u/Trying_to_learn)
#### Post date: [26 September 2020 08:01 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364/5 "2020-09-26T08:01:15Z")
This is the flow as I have it.
Input is the left most `link` node.
output is right most `link` node.
It uses `flow` context to store the RGB values.
External nodes needed:
`node-red-contrib-fan`
`node-red-contrib-simple-gate`
The other two `link` nodes with no names are used to control the `gate` node and a test input to inject values for testing.
```auto
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30","x":1490,"y":1470,"wires":[["69551e43.d2fb7","85accc97.edf778"]]},{"id":"c9de0db3.4da8e","type":"debug","z":"3caae529.4226aa","name":"INPUT","active":false,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","x":1000,"y":1420,"wires":[]},{"id":"edf81695.bba0f","type":"gate","z":"3caae529.4226aa","name":"B","controlTopic":"CONTROL","defaultState":"open","openCmd":"STOP","closeCmd":"GO","toggleCmd":"toggle","defaultCmd":"default","persist":false,"x":870,"y":1470,"wires":[["df0f54b4.0d9e58"]]},{"id":"3dcd710f.3f182e","type":"link in","z":"3caae529.4226aa","name":"","links":["5339afc.acdd9d","6c7fc691.1f2648"],"x":885,"y":1420,"wires":[["df0f54b4.0d9e58"]]},{"id":"167b9ab5.e1a6dd","type":"switch","z":"3caae529.4226aa","name":"> 41","property":"payload","propertyType":"msg","rules":[{"t":"gt","v":"41","vt":"num"},{"t":"else"}],"checkall":"true","repair":false,"outputs":2,"x":1290,"y":1710,"wires":[["31e66410.fc74ac"],["31e66410.fc74ac"]]},{"id":"fdc3827.f99c8","type":"debug","z":"3caae529.4226aa","name":"Blue","active":false,"tosidebar":true,"console":false,"tostatus":false,"complete":"blue","targetType":"msg","x":2050,"y":1430,"wires":[]},{"id":"69551e43.d2fb7","type":"switch","z":"3caae529.4226aa","name":"","property":"payload","propertyType":"msg","rules":[{"t":"gte","v":"0","vt":"num"},{"t":"else"}],"checkall":"true","repair":false,"outputs":2,"x":1640,"y":1470,"wires":[["af0be7a7.3ab1e"],["3be33a29.4220de"]]},{"id":"3be33a29.4220de","type":"change","z":"3caae529.4226aa","name":"0","rules":[{"t":"set","p":"payload","pt":"msg","to":"0","tot":"num"}],"action":"","property":"","from":"","to":"","reg":false,"x":1770,"y":1500,"wires":[["af0be7a7.3ab1e"]]},{"id":"75a4a4a2.d1f824","type":"delay","z":"3caae529.4226aa","name":"","pauseType":"delay","timeout":"1","timeoutUnits":"seconds","rate":"1","nbRateUnits":"1","rateUnits":"second","randomFirst":"1","randomLast":"5","randomUnits":"seconds","drop":false,"x":2110,"y":1470,"wires":[["9626dd05.4b254"]]},{"id":"2eeb5093.0c644","type":"debug","z":"3caae529.4226aa","name":"Red","active":false,"tosidebar":true,"console":false,"tostatus":false,"complete":"red","targetType":"msg","x":2050,"y":1680,"wires":[]},{"id":"179a95bb.552dd2","type":"switch","z":"3caae529.4226aa","name":"","property":"payload","propertyType":"msg","rules":[{"t":"lte","v":"255","vt":"num"},{"t":"lt","v":"0","vt":"num"},{"t":"else"}],"checkall":"true","repair":false,"outputs":3,"x":1640,"y":1720,"wires":[["ab74ba2b.4db098"],["6d6146f2.50f0d"],["6d6146f2.50f0d"]]},{"id":"6d6146f2.50f0d","type":"change","z":"3caae529.4226aa","name":"0","rules":[{"t":"set","p":"payload","pt":"msg","to":"0","tot":"num"}],"action":"","property":"","from":"","to":"","reg":false,"x":1770,"y":1740,"wires":[["ab74ba2b.4db098"]]},{"id":"85accc97.edf778","type":"debug","z":"3caae529.4226aa","name":"blue","active":false,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","x":1640,"y":1430,"wires":[]},{"id":"35fb326e.b2e8f6","type":"gate","z":"3caae529.4226aa","name":"B","controlTopic":"CONTROL","defaultState":"open","openCmd":"STOP","closeCmd":"GO","toggleCmd":"toggle","defaultCmd":"default","persist":true,"x":740,"y":1470,"wires":[["edf81695.bba0f"]]},{"id":"54da435d.ca930c","type":"inject","z":"3caae529.4226aa","name":"B","topic":"CONTROL","payload":"STOP","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":1440,"y":1930,"wires":[["edf81695.bba0f"]]},{"id":"6e771919.9838e8","type":"inject","z":"3caae529.4226aa","name":"A","topic":"CONTROL","payload":"GO","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":"1","x":1440,"y":1890,"wires":[["edf81695.bba0f"]]},{"id":"31e66410.fc74ac","type":"range","z":"3caae529.4226aa","minin":"40","maxin":"75","minout":"10","maxout":"255","action":"scale","round":true,"property":"payload","name":"40 - 75","x":1490,"y":1720,"wires":[["179a95bb.552dd2"]]},{"id":"9626dd05.4b254","type":"function","z":"3caae529.4226aa","name":"","func":"//node.warn(msg);\n\n//if (msg.red !== null)\n//{\n// context.set(\"RED\",msg.red);\n// node.warn(\"Red set\");\n//} else\n//if (msg.green !== null)\n//{\n// context.set(\"GREEN\",msg.green);\n// node.warn(\"Green set\");\n//} else\n//if (msg.blue !== null)\n//{\n// context.set(\"BLUE\",msg.blue);\n// node.warn(\"Blue set\");\n//}\nif (flow.get(\"RED\") !== null && flow.get(\"GREEN\") !== null && flow.get(\"BLUE\") !== null)\n{\n msg = {\n red:flow.get(\"RED\"),\n green:flow.get(\"GREEN\"),\n blue:flow.get(\"BLUE\"),\n Temperature_LED:flow.get(\"Temperature_LED\")\n }\n flow.set(\"RED\",null);\n flow.set(\"GREEN\",null);\n flow.set(\"BLUE\",null);\n return msg;\n}\n","outputs":1,"noerr":0,"x":2240,"y":1540,"wires":[["7ef4c417.22ac3c","f045c230.d9b2f8"]]},{"id":"7a42bcc1.3079bc","type":"link in","z":"3caae529.4226aa","name":"Temperature RX","links":["29785c87.2f304c"],"x":560,"y":1470,"wires":[["35fb326e.b2e8f6"]],"l":true},{"id":"2043a922.c8e486","type":"link in","z":"3caae529.4226aa","name":"","links":["50922805.64c078"],"x":615,"y":1420,"wires":[["35fb326e.b2e8f6"]]},{"id":"7ef4c417.22ac3c","type":"debug","z":"3caae529.4226aa","name":"","active":false,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","x":2380,"y":1470,"wires":[]},{"id":"f045c230.d9b2f8","type":"template","z":"3caae529.4226aa","name":"","field":"payload","fieldType":"msg","format":"handlebars","syntax":"mustache","template":"{{Temperature_LED}},{{red}},{{green}},{{blue}}","output":"str","x":2390,"y":1540,"wires":[["f70a880e.1468a","34a781d1.813346"]]},{"id":"f70a880e.1468a","type":"debug","z":"3caae529.4226aa","name":"RGB","active":false,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","x":2570,"y":1470,"wires":[]},{"id":"34a781d1.813346","type":"gate","z":"3caae529.4226aa","name":"B","controlTopic":"CONTROL","defaultState":"open","openCmd":"STOP","closeCmd":"GO","toggleCmd":"toggle","defaultCmd":"default","persist":false,"x":2570,"y":1540,"wires":[["93b63ed3.cf2b7"]]},{"id":"7f455dc3.82d3e4","type":"inject","z":"3caae529.4226aa","name":"B","topic":"CONTROL","payload":"STOP","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":2400,"y":1630,"wires":[["34a781d1.813346"]]},{"id":"628200d4.4588a8","type":"inject","z":"3caae529.4226aa","name":"A","topic":"CONTROL","payload":"GO","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":"1","x":2400,"y":1590,"wires":[["34a781d1.813346"]]},{"id":"93b63ed3.cf2b7","type":"link out","z":"3caae529.4226aa","name":"","links":["edf7b494.05e39"],"x":2675,"y":1540,"wires":[]}]
```
---
### Author:  [@Steve-Mcl](https://discourse.nodered.org/u/Steve-Mcl)
#### Post date: [26 September 2020 08:05 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364/6 "2020-09-26T08:05:23Z")
Andrew, have a look at [this post](https://discourse.nodered.org/t/how-to-generate-an-image-from-the-8x8-raw-heat-map-data-of-an-amg8833-thermal-sensor/31604/8). In the colourise function is some code you can adapt to generate a heat colour.
---
### Author:  [@Colin](https://discourse.nodered.org/u/Colin)
#### Post date: [26 September 2020 08:10 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364/7 "2020-09-26T08:10:36Z")
What has all that got to do with the question here, which is how to map an input value of 30 to 75 to give you RGB values? All you need to test that is a slider (or inject nodes) and the logic to generate the colours.
---
### Author:  [@Trying\_to\_learn](https://discourse.nodered.org/u/Trying_to_learn)
#### Post date: [26 September 2020 08:12 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364/8 "2020-09-26T08:12:39Z")
Sorry, was that to me or Steve?
The reply is to me, so I am not sure.
---
### Author:  [@Colin](https://discourse.nodered.org/u/Colin)
#### Post date: [26 September 2020 08:14 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364/9 "2020-09-26T08:14:18Z")
It is to you, you posted a flow with an explanation of what it does, including using non-core nodes, but that doesn't seem to have anything to do with question you asked, which is how to map a number to RGB values.
---
### Author:  [@Trying\_to\_learn](https://discourse.nodered.org/u/Trying_to_learn)
#### Post date: [26 September 2020 08:18 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364/10 "2020-09-26T08:18:25Z")
I use non-core nodes because a: the allow me to isolate the real data from fake data I am injecting. and b) I like the `fan` node as it allows me to _sectionalise_ parts of the code and allow me to move blocks easily.
I know the newer version allows something like that, but it is annoying if/when I have a node with (say) 10 inputs and it is the wrong kind.
I have to delete all the connections to it when I put in a new node and then wire all the inputs to it.
The `fan` node allows me to have the _inputs_ all connected together and allow me to easily delete/replace the node.
We seem to be having a bit of misunderstanding.
---
### Author:  [@Colin](https://discourse.nodered.org/u/Colin)
#### Post date: [26 September 2020 08:28 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364/11 "2020-09-26T08:28:02Z")
> [@Trying\_to\_learn](#):
>
> We seem to be having a bit of misunderstanding.
Yes we do. The title of this thread is Colour mapping - help needed to create RGB value. In the first post you said you had a value in the range 30-75 and you want to map that to RGB values. The fan node and those before it and everything after the delay node appear to have nothing to do with that.
I believe you can simplify the bit in the middle dramatically if you set the range node to Scale and Limit mode, as I said earlier.
However, @Steve-Mcl's link looks as if it might give some better ideas.
---
### Author:  [@Trying\_to\_learn](https://discourse.nodered.org/u/Trying_to_learn)
#### Post date: [26 September 2020 08:33 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364/12 "2020-09-26T08:33:29Z")
I am really struggling to understand it.
I get the idea in a vague way, but seem to be failing getting the real mechanics nailed down.
I use `switch` nodes and `range` nodes to do things, but I seem to not be able to get things working as desired.
I have built several examples where I send sequential date (31 - 75 sequentially) to see how it works, but there are a lot of pot holes in it.
Thus I am asking for help.
---
### Author:  [@Steve-Mcl](https://discourse.nodered.org/u/Steve-Mcl)
#### Post date: [26 September 2020 08:47 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364/13 "2020-09-26T08:47:37Z")
Here is an adaption of that code.
As you didnt specify how you want RGB to be represented, I just spit out a whole bunch of different values (r,g,b,val,hex) in the payload object.
Ignore the pink image nodes at the bottom - they are to demonstrate it working.
```auto
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```
---
### Author:  [@Trying\_to\_learn](https://discourse.nodered.org/u/Trying_to_learn)
#### Post date: [26 September 2020 08:53 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364/14 "2020-09-26T08:53:39Z")
@Steve-Mcl
Thanks.
It looks nice and I just gave it a quick _butcher's hook_ (Look)
Now I have to apply it to the _real world_ and see how it goes.
But I think you have the maths part down pat.
Much appreciated.
---
### Author:  [@Trying\_to\_learn](https://discourse.nodered.org/u/Trying_to_learn)
#### Post date: [26 September 2020 09:08 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364/15 "2020-09-26T09:08:43Z")
I may have to play with it to tweak where/when/how the colours appear.
But that does seem to do what I want.
---
### Author:  [@system](https://discourse.nodered.org/u/system)
#### Post date: [10 October 2020 09:08 UTC](https://discourse.nodered.org/t/colour-mapping-help-needed-to-create-rgb-value/33364/16 "2020-10-10T09:08:47Z")
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