4 gray scale(2 bits) display color settings

How-to
1

Hi everyone,

I am new at lvgl. I use lvgl 8.3 version with c language. I am a litte bit confused about drive my 4 gray scale display(2 bits for each color). The available colors for my display are 00(black), 01(dark gray), 10(light gray), 11(white).

I have wrote a set_px_cb function to update the buffer according to my display (waveshare 4.2 inch e-ink). But I am confused about color settings. What should be the color depth and how should I map color to 2 bits.

Thank you for your help. I am gladful for your support!

2

Hi @Zeyzey ,

I am no expert at this but I think you need to do something like this, which expands on the monochrome example in the documentation here:

void set_px_cb(lv_disp_drv_t * disp_drv, uint8_t * buf, lv_coord_t buf_w, lv_coord_t x, lv_coord_t y, lv_color_t color, lv_opa_t opa)
{
   buf += buf_w * (y >> 3) + x;
   if(lv_color_brightness(color) < 64) (*buf) = 0b00;
   else if(lv_color_brightness(color) >= 64 && lv_color_brightness(color) < 128 ) (*buf) = 0b01;
   else if(lv_color_brightness(color) >= 128 && lv_color_brightness(color) < 192 ) (*buf) = 0b10;
   else if(lv_color_brightness(color) >= 192 ) (*buf) = 0b11;
}

This should work with 24-bit/32-bit RGB colours, you can probably experiment with different formats to see which gives the best performance versus image quality. I am unsure how you have implemented your buffer logic so you may need to adjust the code to suite your implementation but hopefully you can see from this what to do.

Cheers,

Pete

3

@pete-pjb thank you :). It was really helpful

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