diff --git a/components/esp_lcd/src/esp_lcd_panel_nt35510.c b/components/esp_lcd/src/esp_lcd_panel_nt35510.c
index 3bae8dae1b..7900d3f3fc 100644
--- a/components/esp_lcd/src/esp_lcd_panel_nt35510.c
+++ b/components/esp_lcd/src/esp_lcd_panel_nt35510.c
@@ -38,7 +38,7 @@ typedef struct {
     bool reset_level;
     int x_gap;
     int y_gap;
-    unsigned int bits_per_pixel;
+    uint8_t fb_bits_per_pixel;
     uint8_t madctl_val; // save current value of LCD_CMD_MADCTL register
     uint8_t colmod_cal; // save surrent value of LCD_CMD_COLMOD register
 } nt35510_panel_t;
@@ -71,15 +71,20 @@ esp_err_t esp_lcd_new_panel_nt35510(const esp_lcd_panel_io_handle_t io, const es
         break;
     }
 
+    uint8_t fb_bits_per_pixel = 0;
     switch (panel_dev_config->bits_per_pixel) {
-    case 16:
+    case 16: // RGB565
         nt35510->colmod_cal = 0x55;
+        fb_bits_per_pixel = 16;
         break;
-    case 18:
+    case 18: // RGB666
         nt35510->colmod_cal = 0x66;
+        // each color component (R/G/B) should occupy the 6 high bits of a byte, which means 3 full bytes are required for a pixel
+        fb_bits_per_pixel = 24;
         break;
-    case 24:
+    case 24: // RGB888
         nt35510->colmod_cal = 0x77;
+        fb_bits_per_pixel = 24;
         break;
     default:
         ESP_GOTO_ON_FALSE(false, ESP_ERR_NOT_SUPPORTED, err, TAG, "unsupported pixel width");
@@ -87,7 +92,7 @@ esp_err_t esp_lcd_new_panel_nt35510(const esp_lcd_panel_io_handle_t io, const es
     }
 
     nt35510->io = io;
-    nt35510->bits_per_pixel = panel_dev_config->bits_per_pixel;
+    nt35510->fb_bits_per_pixel = fb_bits_per_pixel;
     nt35510->reset_gpio_num = panel_dev_config->reset_gpio_num;
     nt35510->reset_level = panel_dev_config->flags.reset_active_high;
     nt35510->base.del = panel_nt35510_del;
@@ -202,7 +207,7 @@ static esp_err_t panel_nt35510_draw_bitmap(esp_lcd_panel_t *panel, int x_start,
         (y_end - 1) & 0xFF,
     }, 2);
     // transfer frame buffer
-    size_t len = (x_end - x_start) * (y_end - y_start) * nt35510->bits_per_pixel / 8;
+    size_t len = (x_end - x_start) * (y_end - y_start) * nt35510->fb_bits_per_pixel / 8;
     esp_lcd_panel_io_tx_color(io, LCD_CMD_RAMWR << 8, color_data, len);
 
     return ESP_OK;
diff --git a/components/esp_lcd/src/esp_lcd_panel_st7789.c b/components/esp_lcd/src/esp_lcd_panel_st7789.c
index e182f969c8..e34957e026 100644
--- a/components/esp_lcd/src/esp_lcd_panel_st7789.c
+++ b/components/esp_lcd/src/esp_lcd_panel_st7789.c
@@ -38,7 +38,7 @@ typedef struct {
     bool reset_level;
     int x_gap;
     int y_gap;
-    unsigned int bits_per_pixel;
+    uint8_t fb_bits_per_pixel;
     uint8_t madctl_val; // save current value of LCD_CMD_MADCTL register
     uint8_t colmod_cal; // save surrent value of LCD_CMD_COLMOD register
 } st7789_panel_t;
@@ -71,12 +71,16 @@ esp_err_t esp_lcd_new_panel_st7789(const esp_lcd_panel_io_handle_t io, const esp
         break;
     }
 
+    uint8_t fb_bits_per_pixel = 0;
     switch (panel_dev_config->bits_per_pixel) {
-    case 16:
+    case 16: // RGB565
         st7789->colmod_cal = 0x55;
+        fb_bits_per_pixel = 16;
         break;
-    case 18:
+    case 18: // RGB666
         st7789->colmod_cal = 0x66;
+        // each color component (R/G/B) should occupy the 6 high bits of a byte, which means 3 full bytes are required for a pixel
+        fb_bits_per_pixel = 24;
         break;
     default:
         ESP_GOTO_ON_FALSE(false, ESP_ERR_NOT_SUPPORTED, err, TAG, "unsupported pixel width");
@@ -84,7 +88,7 @@ esp_err_t esp_lcd_new_panel_st7789(const esp_lcd_panel_io_handle_t io, const esp
     }
 
     st7789->io = io;
-    st7789->bits_per_pixel = panel_dev_config->bits_per_pixel;
+    st7789->fb_bits_per_pixel = fb_bits_per_pixel;
     st7789->reset_gpio_num = panel_dev_config->reset_gpio_num;
     st7789->reset_level = panel_dev_config->flags.reset_active_high;
     st7789->base.del = panel_st7789_del;
@@ -186,7 +190,7 @@ static esp_err_t panel_st7789_draw_bitmap(esp_lcd_panel_t *panel, int x_start, i
         (y_end - 1) & 0xFF,
     }, 4);
     // transfer frame buffer
-    size_t len = (x_end - x_start) * (y_end - y_start) * st7789->bits_per_pixel / 8;
+    size_t len = (x_end - x_start) * (y_end - y_start) * st7789->fb_bits_per_pixel / 8;
     esp_lcd_panel_io_tx_color(io, LCD_CMD_RAMWR, color_data, len);
 
     return ESP_OK;