Color picker returns unexpected RGB values

General discussion
1

I’m using LVGL on a TFT display with an Arduino. I’m trying to get the RGB values from the color picker widget. The code seems to be working, but it’s returning unexpected values. I can’t seem to figure out what I’m missing or how I’m interpreting the data incorrectly.

lv_color_t selectedColor = lv_colorwheel_get_rgb(ui_colorWheel);
  uint8_t red = selectedColor.ch.red;
  uint8_t green = selectedColor.ch.green;
  uint8_t blue = selectedColor.ch.blue;
  Serial.print("Color changed to RGB: ");
  Serial.println(red);
  Serial.println(green);
  Serial.println(blue);

When the color wheel selection is basically red (hard to get it exact), the output is:

Color changed to RGB: 31
3
0

I would expect something more like 255 for the red value. I know it’s red because later in the code I set the text color to the color wheel selection. What am I missing?

Setting it to yellow-ish, the output is:

Color changed to RGB: 30
63
0

I’m not understanding something. Any help is appreciated! Thanks

2

I get the same problem , does it should be 0 -255, it seems that the big value is 31
Here is the code I get rgb value :
uint16_t out[3];
lv_color_t c = lv_colorwheel_get_rgb(ui_Colorwheel3);
out[0] = LV_COLOR_GET_R(c);
out[1] = LV_COLOR_GET_G(c);
out[2] = LV_COLOR_GET_B(c);

3

Hello,

I am not sure what “LV_COLOR_GET_x” does… though I can guess.

But why not just get the values from the struct directly? By the way, the lv_color_t struct consists of the following: Colors — LVGL documentation

So it is just three bytes, I figure the problem here is possible casting.

Try this:

uint8_t out[3];
lv_color_t c = lv_colorwheel_get_rgb(ui_Colorwheel3);
out[0] = c.r;
out[1] = c.g;
out[2] = c.b;
4

Here is my LVGL version :
#define LVGL_VERSION_MAJOR 8

#define LVGL_VERSION_MINOR 3

#define LVGL_VERSION_PATCH 6

#define LVGL_VERSION_INFO “”

uint8_t out[3];
lv_color_t c = lv_colorwheel_get_rgb(ui_Colorwheel3);
out[0] = c.r;
out[1] = c.g;
out[2] = c.b;
or
out[0] = c.red;
out[1] = c.green;
out[2] = c.blue;

I have try and cannot compile:
E:/project/TFT_BW8625/TFT_BW8625/main/ui.c:848:20: error: ‘lv_color_t’ {aka ‘union ’} has no member named ‘r’
out[0] = c.r;
^
E:/project/TFT_BW8625/TFT_BW8625/main/ui.c:849:20: error: ‘lv_color_t’ {aka ‘union ’} has no member named ‘g’
out[1] = c.g;
^
E:/project/TFT_BW8625/TFT_BW8625/main/ui.c:850:20: error: ‘lv_color_t’ {aka ‘union ’} has no member named ‘b’
out[2] = c.b;
attached file is lv_color.h file.
lv_color.h (22.8 KB)

5

Excuse me, I notice now that it should be out[0] = c.red etc.
That should work, I see it in you code snippet also but have you tried that?

6

yes , have tried and cannot compile . You can check my lv_color.h , it doesn’t have member red green and blue . Below is the log :

E:/project/TFT_BW8625/TFT_BW8625/main/ui.c:848:20: error: ‘lv_color_t’ {aka ‘union ’} has no member named ‘red’
out[0] = c.red;
^
E:/project/TFT_BW8625/TFT_BW8625/main/ui.c:849:20: error: ‘lv_color_t’ {aka ‘union ’} has no member named ‘green’
out[1] = c.green;
^
E:/project/TFT_BW8625/TFT_BW8625/main/ui.c:850:20: error: ‘lv_color_t’ {aka ‘union ’} has no member named ‘blue’
out[2] = c.blue;
^

7

Hello,

Very strange. Perhaps it should be out[0] = c.ch.red etc? That’s what I can gather from this post: How to extract RGB values from colorpicker widget? - #3 by skartalov

Sadly I only have V9 running at the moment in which this color picker does not exist anymore. If this does not help then I do not have any more ideas.

8

Thanks .
It can use
out[0] = c.ch.red;
out[1] = c.ch.green_h;
out[2] = c.ch.blue;
to get color value ,but it is the same value as what I have got before:

image
image953×347 28.3 KB

9

What is your color depth? I think it has to do with that. For instance if you use 16-bit color the values here will be as follows:

red: 5 bits      (max.   11111  = 31)
green: 6 bits    (max.   111111 = 63)
blue: 5 bits     (max.   11111  = 31)

You may have to convert it to 32-bit color. You might try lv_color_to32.
See this bit of the documentation (convert color): Colors — LVGL documentation

10

Thanks ,it works ok now :
if(event_code == LV_EVENT_VALUE_CHANGED){
uint16_t out[3];
lv_color32_t c32;
lv_color_t c = lv_colorwheel_get_rgb(ui_Colorwheel3);
c32.full = lv_color_to32(c);
out[0] = c32.ch.red;
out[1] = c32.ch.green;
out[2] = c32.ch.blue;
ESP_LOGW(TAG_, “RGB: %d / %d / %d \r\n”, out[0], out[1], out[2] );
}