It's abnormal to add a gradient icon on tranparent background

How-to
1

I’m trying to add a gradient icon passenger_alarm.png on a total transparent background.
passenger_alarm

After that flush the widgets data in flush_cb.
However, it seem to be abnormal when I’ve got these widgets data. All the value of Alpha are 0xFF.
rgba_data_flush_from_lvgl.txt (80.4 KB)

I made it like this:

  1. Make a transparent background:
    lv_obj_set_style_bg_opa(lv_scr_act(), LV_OPA_TRANSP, LV_PART_MAIN);
    lv_disp_set_bg_opa(NULL, LV_OPA_TRANSP);

    lv_obj_t* top_vision = lv_img_create(lv_scr_act());
    lv_obj_set_pos(top_vision, 0, 0);
    lv_obj_set_size(top_vision, 294, 70);

  2. Add a image on background:
    lv_obj_t* disp_left = lv_img_create(top_vision);
    lv_img_set_src(disp_left, “…/resources/passenger_alarm.png”);
    lv_obj_set_pos(disp_left, 0, 0);
    lv_obj_set_size(disp_left, 294, 70);
    lv_obj_set_style_bg_color(disp_left, lv_color_make(255, 0, 0), 0);
    lv_obj_set_style_bg_opa(disp_left, LV_OPA_TRANSP, LV_PART_ANY);

  3. Found out that the Alpha of gradient is always 0xFF. I’ve tried to save down it as png, via opencv’s cv::imwrite for example, it likes this:
    rgba_data_flush_from_lvgl

The Gradient was lost!
How can I do to make this gradient normal？

I’ve also uploaded the main.c of my sample.
main.c (5.3 KB)
Thx！