Hi, Can someone explain why the following peace of code does NOT produce 60

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1

Hi,
Can someone explain why the following peace of code does NOT produce 60 evenly lid led’s in terms of brightness?

#include “FastLED.h”
#define NUM_LEDS 60
#define DATA_PIN 10
CRGB leds[NUM_LEDS];

void setup(){
LEDS.addLeds<WS2812B, DATA_PIN, RGB>(leds, NUM_LEDS);
}

void loop (){

//set even led’s
for(int i=0; i<60; i=i+2) leds[i].setHSV(160, 255, 50); //minValue=16

//set odd led’s
for(int j=1; j<60; j=j+2) leds[j].setHue(160);
for(int j=1; j<60; j=j+2) leds[j] %=50; //minValue=2

FastLED.show(); //update ALL led’s
}

The most dim value for the EVEN led’s seems to be 16 and for the ODD led’s a value of 2. The upper limit for both is 255. The fadingcurve is not linear.

2

Because setHue probably makes the brightness 255 and not 50.

3

And also because the HSV to RGB conversion will attempt to (roughly) provide a non-linear curve to brightness, whereas the %= is just a straight scale8 of the rgb values. (Well, technically, scale8 video, but for the purposes here, they’re effectively the same thing).

4

if you changed the led[j] %= 50; to led[j] %= scale8_video(50,50); you’d probably get something that matches up a bit closer. Roughly.

5

Okay…
Here’s what I got. I came up with this RGB clock. It’s level is controlled by a LDR. It’s analog reading is mapped three times: first 50-200 being the hands(red green, blue), second 50-100 all “remaining” led’s and last 200-0 being an inverted saturation for the same “remaining” led’s. So, during the day the saturation for the remaining 57 led’s is close to zero: they go white. During the night their saturation fades to value 200 and turn blue AND dim as well. Needing to be able so set a saturation level, I have to use the CHSV object. There is no “set.Sat” like there is “set.Hue”.

6

@Kasper_Kamperman
If setHue controls brightness, what controls hue? This doesn’t make sense to me.
In the above code , hue stays the same throughout and the led’s behave accordingly. It’s the dimming (if I change the values simultaneously) that doesn’t run smooth. Is there a way to control both hue AND saturation in a mathematical way so I can assign a value to both separately? setHue and % do it in a nice way, but setHSV not.

7

I don’t understand why you can’t use setHSV? You can keep track of hue, saturation and brightness yourself in your Arduino code?

Or you can make a CHSV variable:
CHSV myHSVcolor;
myHSVcolor.hue = 0;
myHSVcolor.saturation = 255;
myHSVcolor.brightness = 255;

Check the wiki for good examples:

What doesn’t run smooth? Maybe you can make a little video to show what’s going on and describe what you expect.

8

I can use HSV but it doesn’t give the same output as setHue and % combined.
When using HSV, the level “kicks in” at level 16, whereas % does a better job starting at 2 (out of 255). I just made a video showing the difference. Let me see if I can upload it :slight_smile:

9

Video is shot with code below. I turn a pot from min to max.

#include “FastLED.h”
#define NUM_LEDS 60
#define DATA_PIN 10
CRGB leds[NUM_LEDS];
int brightness;

void setup() {
delay(1000); //safety first!
LEDS.addLeds<WS2812B, DATA_PIN, GRB>(leds, NUM_LEDS);}

void loop (){
// brightness through pot
brightness = map((analogRead(A6)), 0, 1023, 0, 255);

//all LED’s to black
for(int i=0; i<60; i=i++) leds[i].setHSV(0, 0, 0);

//all EVEN led’s
for(int i=0; i<60; i=i+2) leds[i].setHSV(161,255,(brightness));

//all ODD led’s
for(int i=1; i<60; i=i+2) leds[i].setHue(161);
for(int i=1; i<60; i=i+2) leds[i]%=(brightness);

FastLED.show(); //update ALL led’s
}

My point is, that if I want to control saturation for any led, I have to use HSV. But specifying hue and % gives much better control, but no saturation control!

10

%= uses video_scaling (sorry, I always read modulo when I see this, so I struggled a bit to understand this part.
But according to the documentation (https://github.com/FastLED/FastLED/wiki/Pixel-reference) you’ll do this:
leds[i].nscale8_video( 192);

In the HSV2RGB conversion there isn’t any non-lineair curve applied right now (at least in the 2.1 branch) I think. I thought that this would be the case, but it’s not.

Best thing to do is to apply the non-lineair scaling to your brightness by using the dim8_video function.

So:
for(int i=0; i<60; i=i+2) leds[i].setHSV(161,255,dim8_video(brightness));

11

Okay, I’ll give it a try. BUT this still leaves me with the saturation part. How do I control the sat for a given led while NOT using the setHSV command? I can set the level (%=) for a specific led, I can set the hue (setHue) but not it’s saturation. How so set the saturation for any given led using a single value?

12

With the setHSV function you can…

But if you want to desaturate RGB colors:
I adapted myself code to change saturation, it’s pretty simple:

red = qadd8(red, saturation);
green = qadd8(green, saturation);
blue = qadd8(blue, saturation);

So it would become:

saturation = dim8_raw(saturation); // this could work nicer, non-lineair curve

leds[i].r = qadd8(leds[i].r, saturation);
leds[i].g = qadd8(leds[i].g, saturation);
leds[i].b = qadd8(leds[i].b, saturation);

qadd8 limits automatically to 255. Check lib8tion.h.

You might want to invert saturation. Because saturation 255 becomes fully white.

13

Hsv2rgb does do a non-linear curve. (V = scale8(V,V); does a quick approximation of that) - this is why there’s a difference between the two sets of code used.

14

@Daniel_Garcia @Mark_Kriegsman Ok. I always assumed that scale8 was linear from this explanation in the lib8tion.h : scale8( i, sc) == (i * sc) / 256

If scale8 is indeed non-lineair than this could be the explanation of my problem? https://plus.google.com/100115767703084101160/posts/ceLmqbpxRUG

15

Right - read the line I posted again - hsv2rgb pre-scales brightness before using it - V=scale8(V,V);

So:

X = scale8(X,V); // linear curve
Y = scale8(Y,scale8(V,V)); // non-linear

The second is what hsv2rgb does.

16

Hi guys,
I took Kasper’s advice on desaturating colors and it works like charme! Now I have a nice looking curve, can control hue, sat and level in fine detail.
Thanks to Kasper and Daniel!

17

@Roger_M Glad I could help! Did you use dim8_raw as well?

Daniel, Mark I’m checking the hsv2rgb code. Is the non-lineair scaling only implemented in the default hsv2rgb_rainbow? Because I can’t find it in the hsv2rgb_raw (that was the one I was using and which had some strange behavior after applying a dim_curve to the rgb values).

18

dim8_raw it is! At least for my application. The clock runs smooth, dims well and all colors look very much alive and balanced. Color is all about math… :wink:

19

The non linear scaling is only done in rainbow for now.