BITMAP quality gets reduced

no-reply@allegro.cc (Doctor Cop) — Sun, 14 Apr 2019 21:08:03 +0000

When I loaded a jpeg image just to test how would background saturation work, I found that the loaded bitmap was of low quality.

Why?

Loaded Bitmap :
{"name":"611992","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/f\/9\/f971ae09ba823aa93534e6a40129591b.png","w":810,"h":629,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/f\/9\/f971ae09ba823aa93534e6a40129591b"}

Original Bitmap :
{"name":"611993","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/3\/1\/312fce8349c30c06f886f11d9de7ddfb.jpg","w":4896,"h":3264,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/3\/1\/312fce8349c30c06f886f11d9de7ddfb"}

no-reply@allegro.cc (Elias) — Sun, 14 Apr 2019 21:30:36 +0000

The scaling algorithm. The original is 4896x3264 pixel, your screenshot is 810x629 pixel. I assume you are drawing it with al_draw_scaled_bitmap?

In that case try calling this before loading the bitmap:

al_set_new_bitmap_flags(ALLEGRO_MIN_LINEAR);

That should make Allegro use linear scaling.

no-reply@allegro.cc (Doctor Cop) — Mon, 15 Apr 2019 07:23:26 +0000

This didn't work.

al_set_new_bitmap_flags(ALLEGRO_MIN_LINEAR);

didn't do anything. Do I need to convert my image file's size?

no-reply@allegro.cc (Edgar Reynaldo) — Mon, 15 Apr 2019 19:30:37 +0000

I can't even tell the difference between the two images. :/

Allegro will load the file at the same resolution it is in.

ALLEGRO_MIN_LINEAR will make allegro use linear filtering when reducing the image size. This can look better than nearest neighbor.

Show more code.

no-reply@allegro.cc (Doctor Cop) — Wed, 17 Apr 2019 18:12:53 +0000

#SelectExpand
  1#include 
  2#include 
  3#include 
  4#include 
  5#include 
  6
  7#define MAXWIDTH 800
  8#define MAXHEIGHT 600
  9
 10int main()
 11{
 12    al_init();
 13    al_init_primitives_addon();
 14    al_init_image_addon();
 15    al_init_font_addon();
 16    al_init_ttf_addon();
 17    al_install_keyboard();
 18    al_install_mouse();
 19
 20    ALLEGRO_DISPLAY *display = al_create_display(MAXWIDTH, MAXHEIGHT);
 21    ALLEGRO_EVENT_QUEUE *queue = al_create_event_queue();
 22    ALLEGRO_TIMER *timer = al_create_timer(2.0/60.0);
 23    ALLEGRO_COLOR black = al_map_rgb(0, 0, 0);
 24    ALLEGRO_FONT *font = al_load_ttf_font("res/L.ttf", 14, 1);
 25    ALLEGRO_BITMAP *background = al_load_bitmap("res/background.jpg");
 26    int x=0, y=0, main_loop = true;
 27
 28    al_register_event_source(queue, al_get_display_event_source(display));
 29    al_register_event_source(queue, al_get_mouse_event_source());
 30    al_register_event_source(queue, al_get_keyboard_event_source());
 31    al_register_event_source(queue, al_get_timer_event_source(timer));
 32
 33    al_start_timer(timer);
 34
 35    while(main_loop)
 36    {
 37        ALLEGRO_EVENT event;
 38
 39        //if(al_is_event_queue_empty(queue))
 40        al_wait_for_event(queue, &event);
 41
 42        if(event.type == ALLEGRO_EVENT_DISPLAY_CLOSE)
 43            main_loop = false;
 44
 45        if(event.type == ALLEGRO_EVENT_TIMER)
 46        {
 47        al_clear_to_color(al_map_rgb(218, 112, 214));
 48
 49        al_set_new_bitmap_flags(ALLEGRO_MIN_LINEAR);
 50
 51        al_draw_scaled_bitmap(background, 0, 0, 4896, 3264, 0, 0, 800, 600, 0);
 52        //al_draw_rounded_rectangle(400-100 + x, 300-20, 400+100 + x, 300+20, 20, 20, al_map_rgb(70, 60, 100), 2);
 53        //al_draw_filled_rectangle(0, 0, 50, 50, al_map_rgb(255, 255, 255));
 54        //al_draw_filled_rectangle(0, 50, 50, MAXHEIGHT, al_map_rgb(255, 0, 255));
 55        //al_draw_line(50, 0, 50, MAXHEIGHT, black, 1);
 56
 57
 58        al_flip_display();
 59        al_rest(0.02);
 60        }
 61
 62        if(event.type == ALLEGRO_EVENT_KEY_DOWN)
 63        {
 64            switch(event.keyboard.keycode)
 65            {
 66                case ALLEGRO_KEY_ESCAPE :
 67                    exit(1);
 68                    break;
 69            }
 70        }
 71
 72    }
 73
 74    al_destroy_display(display);
 75    al_destroy_event_queue(queue);
 76    return 0;
 77}

no-reply@allegro.cc (Edgar Reynaldo) — Wed, 17 Apr 2019 18:45:16 +0000

Doctor Cop said:

 al_set_new_bitmap_flags(ALLEGRO_MIN_LINEAR);

You have to call this BEFORE loading your bitmap.

THEN when it gets drawn it will be multisampled.

no-reply@allegro.cc (Doctor Cop) — Wed, 17 Apr 2019 20:05:22 +0000

Thanks, Edgar, it worked just fine. although there is still some noise but its smoother than before.

no-reply@allegro.cc (Elias) — Wed, 17 Apr 2019 23:00:00 +0000

Yes, linear scaling is not the highest quality. If this is for something like background pictures for a game you could maybe provide pre-scaled versions for smaller resolutions. At least then you'd only have to use a little bit of linear scaling - I imagine that would still look better than scaling down from the 4K resolution (not completely sure - but easy to try).