Image (lv_img)

Overview

Images are the basic object to display images from flash (as arrays) or from files. Images can display symbols (LV_SYMBOL_...) too.

Using the Image decoder interface custom image formats can be supported as well.

Parts and Styles

  • LV_PART_MAIN A background rectangle that uses the typical background style properties and the image itself using the image style properties.

Usage

Image source

To provide maximum flexibility, the source of the image can be:

  • a variable in code (a C array with the pixels).

  • a file stored externally (e.g. on an SD card).

  • a text with Symbols.

To set the source of an image, use lv_img_set_src(img, src).

To generate a pixel array from a PNG, JPG or BMP image, use the Online image converter tool and set the converted image with its pointer: lv_img_set_src(img1, &converted_img_var); To make the variable visible in the C file, you need to declare it with LV_IMG_DECLARE(converted_img_var).

To use external files, you also need to convert the image files using the online converter tool but now you should select the binary output format. You also need to use LVGL's file system module and register a driver with some functions for the basic file operation. Go to the File system to learn more. To set an image sourced from a file, use lv_img_set_src(img, "S:folder1/my_img.bin").

You can also set a symbol similarly to Labels. In this case, the image will be rendered as text according to the font specified in the style. It enables to use of light-weight monochrome "letters" instead of real images. You can set symbol like lv_img_set_src(img1, LV_SYMBOL_OK).

Label as an image

Images and labels are sometimes used to convey the same thing. For example, to describe what a button does. Therefore, images and labels are somewhat interchangeable, that is the images can display texts by using LV_SYMBOL_DUMMY as the prefix of the text. For example, lv_img_set_src(img, LV_SYMBOL_DUMMY "Some text").

Transparency

The internal (variable) and external images support 2 transparency handling methods:

  • Chroma-keying - Pixels with LV_COLOR_CHROMA_KEY (lv_conf.h) color will be transparent.

  • Alpha byte - An alpha byte is added to every pixel that contains the pixel's opacity

Palette and Alpha index

Besides the True color (RGB) color format, the following formats are supported:

  • Indexed - Image has a palette.

  • Alpha indexed - Only alpha values are stored.

These options can be selected in the image converter. To learn more about the color formats, read the Images section.

Recolor

A color can be mixed with every pixel of an image with a given intensity. This can be useful to show different states (checked, inactive, pressed, etc.) of an image without storing more versions of the same image. This feature can be enabled in the style by setting img_recolor_opa between LV_OPA_TRANSP (no recolor, value: 0) and LV_OPA_COVER (full recolor, value: 255). The default value is LV_OPA_TRANSP so this feature is disabled.

The color to mix is set by img_recolor.

Auto-size

If the width or height of the image object is set to LV_SIZE_CONTENT the object's size will be set according to the size of the image source in the respective direction.

Mosaic

If the object's size is greater than the image size in any directions, then the image will be repeated like a mosaic. This allows creation a large image from only a very narrow source. For example, you can have a 300 x 5 image with a special gradient and set it as a wallpaper using the mosaic feature.

Offset

With lv_img_set_offset_x(img, x_ofs) and lv_img_set_offset_y(img, y_ofs), you can add some offset to the displayed image. Useful if the object size is smaller than the image source size. Using the offset parameter a Texture atlas or a "running image" effect can be created by Animating the x or y offset.

Transformations

Using the lv_img_set_zoom(img, factor) the images will be zoomed. Set factor to 256 or LV_IMG_ZOOM_NONE to disable zooming. A larger value enlarges the images (e.g. 512 double size), a smaller value shrinks it (e.g. 128 half size). Fractional scale works as well. E.g. 281 for 10% enlargement.

To rotate the image use lv_img_set_angle(img, angle). Angle has 0.1 degree precision, so for 45.8° set 458.

The transform_zoom and transform_angle style properties are also used to determine the final zoom and angle.

By default, the pivot point of the rotation is the center of the image. It can be changed with lv_img_set_pivot(img, pivot_x, pivot_y). 0;0 is the top left corner.

The quality of the transformation can be adjusted with lv_img_set_antialias(img, true/false). With enabled anti-aliasing the transformations are higher quality but slower.

The transformations require the whole image to be available. Therefore indexed images (LV_IMG_CF_INDEXED_...), alpha only images (LV_IMG_CF_ALPHA_...) or images from files can not be transformed. In other words transformations work only on true color images stored as C array, or if a custom Image decoder returns the whole image.

Note that the real coordinates of image objects won't change during transformation. That is lv_obj_get_width/height/x/y() will return the original, non-zoomed coordinates.

Events

No special events are sent by image objects.

Learn more about Events.

Keys

No Keys are processed by the object type.

Learn more about Keys.

Example

Image from variable and symbol

Click to try in the MicroPython simulator!
#include "../../lv_examples.h"
#if LV_USE_IMG && LV_BUILD_EXAMPLES


void lv_example_img_1(void)
{
    LV_IMG_DECLARE(img_cogwheel_argb);
    lv_obj_t * img1 = lv_img_create(lv_scr_act());
    lv_img_set_src(img1, &img_cogwheel_argb);
    lv_obj_align(img1, LV_ALIGN_CENTER, 0, -20);
    lv_obj_set_size(img1, 200, 200);

    lv_obj_t * img2 = lv_img_create(lv_scr_act());
    lv_img_set_src(img2, LV_SYMBOL_OK "Accept");
    lv_obj_align_to(img2, img1, LV_ALIGN_OUT_BOTTOM_MID, 0, 20);
}

#endif

MicroPython code     view on GitHub

#!/opt/bin/lv_micropython -i
import sys
import lvgl as lv
import display_driver
from imagetools import get_png_info, open_png

# Register PNG image decoder
decoder = lv.img.decoder_create()
decoder.info_cb = get_png_info
decoder.open_cb = open_png

# Create an image from the png file
try:
    with open('../../assets/img_cogwheel_argb.png','rb') as f:
        png_data = f.read()
except:
    print("Could not find img_cogwheel_argb.png")
    sys.exit()
    
img_cogwheel_argb = lv.img_dsc_t({
  'data_size': len(png_data),
  'data': png_data 
})

img1 = lv.img(lv.scr_act())
img1.set_src(img_cogwheel_argb)
img1.align(lv.ALIGN.CENTER, 0, -20)
img1.set_size(200, 200)

img2 = lv.img(lv.scr_act())
img2.set_src(lv.SYMBOL.OK + "Accept")
img2.align_to(img1, lv.ALIGN.OUT_BOTTOM_MID, 0, 20)

Image recoloring

Click to try in the MicroPython simulator!
#include "../../lv_examples.h"
#if LV_USE_IMG && LV_USE_SLIDER && LV_BUILD_EXAMPLES

static lv_obj_t * create_slider(lv_color_t color);
static void slider_event_cb(lv_event_t * e);

static lv_obj_t * red_slider, * green_slider, * blue_slider, * intense_slider;
static lv_obj_t * img1;


/**
 * Demonstrate runtime image re-coloring
 */
void lv_example_img_2(void)
{
    /*Create 4 sliders to adjust RGB color and re-color intensity*/
    red_slider = create_slider(lv_palette_main(LV_PALETTE_RED));
    green_slider = create_slider(lv_palette_main(LV_PALETTE_GREEN));
    blue_slider = create_slider(lv_palette_main(LV_PALETTE_BLUE));
    intense_slider = create_slider(lv_palette_main(LV_PALETTE_GREY));

    lv_slider_set_value(red_slider, LV_OPA_20, LV_ANIM_OFF);
    lv_slider_set_value(green_slider, LV_OPA_90, LV_ANIM_OFF);
    lv_slider_set_value(blue_slider, LV_OPA_60, LV_ANIM_OFF);
    lv_slider_set_value(intense_slider, LV_OPA_50, LV_ANIM_OFF);

    lv_obj_align(red_slider, LV_ALIGN_LEFT_MID, 25, 0);
    lv_obj_align_to(green_slider, red_slider, LV_ALIGN_OUT_RIGHT_MID, 25, 0);
    lv_obj_align_to(blue_slider, green_slider, LV_ALIGN_OUT_RIGHT_MID, 25, 0);
    lv_obj_align_to(intense_slider, blue_slider, LV_ALIGN_OUT_RIGHT_MID, 25, 0);

    /*Now create the actual image*/
    LV_IMG_DECLARE(img_cogwheel_argb)
    img1 = lv_img_create(lv_scr_act());
    lv_img_set_src(img1, &img_cogwheel_argb);
    lv_obj_align(img1, LV_ALIGN_RIGHT_MID, -20, 0);

    lv_event_send(intense_slider, LV_EVENT_VALUE_CHANGED, NULL);
}

static void slider_event_cb(lv_event_t * e)
{
    LV_UNUSED(e);

    /*Recolor the image based on the sliders' values*/
    lv_color_t color  = lv_color_make(lv_slider_get_value(red_slider), lv_slider_get_value(green_slider), lv_slider_get_value(blue_slider));
    lv_opa_t intense = lv_slider_get_value(intense_slider);
    lv_obj_set_style_img_recolor_opa(img1, intense, 0);
    lv_obj_set_style_img_recolor(img1, color, 0);
}

static lv_obj_t * create_slider(lv_color_t color)
{
    lv_obj_t * slider = lv_slider_create(lv_scr_act());
    lv_slider_set_range(slider, 0, 255);
    lv_obj_set_size(slider, 10, 200);
    lv_obj_set_style_bg_color(slider, color, LV_PART_KNOB);
    lv_obj_set_style_bg_color(slider, lv_color_darken(color, LV_OPA_40), LV_PART_INDICATOR);
    lv_obj_add_event_cb(slider, slider_event_cb, LV_EVENT_VALUE_CHANGED, NULL);
    return slider;
}

#endif

MicroPython code     view on GitHub

#!/opt/bin/lv_micropython -i
import sys
import lvgl as lv
import display_driver
from imagetools import get_png_info, open_png

# Register PNG image decoder
decoder = lv.img.decoder_create()
decoder.info_cb = get_png_info
decoder.open_cb = open_png

# Create an image from the png file
try:
    with open('../../assets/img_cogwheel_argb.png','rb') as f:
        png_data = f.read()
except:
    print("Could not find img_cogwheel_argb.png")
    sys.exit()
    
img_cogwheel_argb = lv.img_dsc_t({
  'data_size': len(png_data),
  'data': png_data 
})

def create_slider(color):
    slider = lv.slider(lv.scr_act())
    slider.set_range(0, 255)
    slider.set_size(10, 200);
    slider.set_style_bg_color(color, lv.PART.KNOB);
    slider.set_style_bg_color(color.color_darken(lv.OPA._40), lv.PART.INDICATOR)
    slider.add_event_cb(slider_event_cb, lv.EVENT.VALUE_CHANGED, None)
    return slider

def slider_event_cb(e):
    # Recolor the image based on the sliders' values
    color  = lv.color_make(red_slider.get_value(), green_slider.get_value(), blue_slider.get_value())
    intense = intense_slider.get_value()
    img1.set_style_img_recolor_opa(intense, 0)
    img1.set_style_img_recolor(color, 0)
    
#
# Demonstrate runtime image re-coloring
#
# Create 4 sliders to adjust RGB color and re-color intensity
red_slider = create_slider(lv.palette_main(lv.PALETTE.RED))
green_slider = create_slider(lv.palette_main(lv.PALETTE.GREEN))
blue_slider = create_slider(lv.palette_main(lv.PALETTE.BLUE))
intense_slider = create_slider(lv.palette_main(lv.PALETTE.GREY))

red_slider.set_value(lv.OPA._20, lv.ANIM.OFF)
green_slider.set_value(lv.OPA._90, lv.ANIM.OFF)
blue_slider.set_value(lv.OPA._60, lv.ANIM.OFF)
intense_slider.set_value(lv.OPA._50, lv.ANIM.OFF)

red_slider.align(lv.ALIGN.LEFT_MID, 25, 0)
green_slider.align_to(red_slider, lv.ALIGN.OUT_RIGHT_MID, 25, 0)
blue_slider.align_to(green_slider, lv.ALIGN.OUT_RIGHT_MID, 25, 0)
intense_slider.align_to(blue_slider, lv.ALIGN.OUT_RIGHT_MID, 25, 0)

# Now create the actual image
img1 = lv.img(lv.scr_act())
img1.set_src(img_cogwheel_argb)
img1.align(lv.ALIGN.RIGHT_MID, -20, 0)

lv.event_send(intense_slider, lv.EVENT.VALUE_CHANGED, None)






Rotate and zoom

Click to try in the MicroPython simulator!
#include "../../lv_examples.h"
#if LV_USE_IMG && LV_BUILD_EXAMPLES

static void set_angle(void * img, int32_t v)
{
    lv_img_set_angle(img, v);
}

static void set_zoom(void * img, int32_t v)
{
    lv_img_set_zoom(img, v);
}


/**
 * Show transformations (zoom and rotation) using a pivot point.
 */
void lv_example_img_3(void)
{
    LV_IMG_DECLARE(img_cogwheel_argb);

    /*Now create the actual image*/
    lv_obj_t * img = lv_img_create(lv_scr_act());
    lv_img_set_src(img, &img_cogwheel_argb);
    lv_obj_align(img, LV_ALIGN_CENTER, 50, 50);
    lv_img_set_pivot(img, 0, 0);    /*Rotate around the top left corner*/

    lv_anim_t a;
    lv_anim_init(&a);
    lv_anim_set_var(&a, img);
    lv_anim_set_exec_cb(&a, set_angle);
    lv_anim_set_values(&a, 0, 3600);
    lv_anim_set_time(&a, 5000);
    lv_anim_set_repeat_count(&a, LV_ANIM_REPEAT_INFINITE);
    lv_anim_start(&a);

    lv_anim_set_exec_cb(&a, set_zoom);
    lv_anim_set_values(&a, 128, 256);
    lv_anim_set_playback_time(&a, 3000);
    lv_anim_start(&a);

}

#endif

MicroPython code     view on GitHub

#!/opt/bin/lv_micropython -i
import sys
import lvgl as lv
import display_driver
from imagetools import get_png_info, open_png

# Register PNG image decoder
decoder = lv.img.decoder_create()
decoder.info_cb = get_png_info
decoder.open_cb = open_png

# Create an image from the png file
try:
    with open('../../assets/img_cogwheel_argb.png','rb') as f:
        png_data = f.read()
except:
    print("Could not find img_cogwheel_argb.png")
    sys.exit()
    
img_cogwheel_argb = lv.img_dsc_t({
  'data_size': len(png_data),
  'data': png_data 
})

def set_angle(img, v):
    img.set_angle(v)

def set_zoom(img, v):
    img.set_zoom(v)


#
# Show transformations (zoom and rotation) using a pivot point.
#

# Now create the actual image
img = lv.img(lv.scr_act())
img.set_src(img_cogwheel_argb)
img.align(lv.ALIGN.CENTER, 50, 50)
img.set_pivot(0, 0)               # Rotate around the top left corner

a1 = lv.anim_t()
a1.init()
a1.set_var(img)
a1.set_custom_exec_cb(lambda a,val: set_angle(img,val))
a1.set_values(0, 3600)
a1.set_time(5000)
a1.set_repeat_count(lv.ANIM_REPEAT.INFINITE)
lv.anim_t.start(a1)

a2 = lv.anim_t()
a2.init()
a2.set_var(img)
a2.set_custom_exec_cb(lambda a,val: set_zoom(img,val))
a2.set_values(128, 256)
a2.set_time(5000)
a2.set_playback_time(3000)
a2.set_repeat_count(LV_ANIM_REPEAT_INFINITE)
lv.anim_t.start(a2)



Image offset and styling

Click to try in the MicroPython simulator!
#include "../../lv_examples.h"
#if LV_USE_IMG && LV_BUILD_EXAMPLES

static void ofs_y_anim(void * img, int32_t v)
{
    lv_img_set_offset_y(img, v);
}

/**
 * Image styling and offset
 */
void lv_example_img_4(void)
{
    LV_IMG_DECLARE(img_skew_strip);

    static lv_style_t style;
    lv_style_init(&style);
    lv_style_set_bg_color(&style, lv_palette_main(LV_PALETTE_YELLOW));
    lv_style_set_bg_opa(&style, LV_OPA_COVER);
    lv_style_set_img_recolor_opa(&style, LV_OPA_COVER);
    lv_style_set_img_recolor(&style, lv_color_black());

    lv_obj_t * img = lv_img_create(lv_scr_act());
    lv_obj_add_style(img, &style, 0);
    lv_img_set_src(img, &img_skew_strip);
    lv_obj_set_size(img, 150, 100);
    lv_obj_center(img);

    lv_anim_t a;
    lv_anim_init(&a);
    lv_anim_set_var(&a, img);
    lv_anim_set_exec_cb(&a, ofs_y_anim);
    lv_anim_set_values(&a, 0, 100);
    lv_anim_set_time(&a, 3000);
    lv_anim_set_playback_time(&a, 500);
    lv_anim_set_repeat_count(&a, LV_ANIM_REPEAT_INFINITE);
    lv_anim_start(&a);

}

#endif

MicroPython code     view on GitHub

from imagetools import get_png_info, open_png

def ofs_y_anim(img, v):    
    img.set_offset_y(v)
    # print(img,v)
    
# Register PNG image decoder
decoder = lv.img.decoder_create()
decoder.info_cb = get_png_info
decoder.open_cb = open_png

# Create an image from the png file
try:
    with open('../../assets/img_skew_strip.png','rb') as f:
        png_data = f.read()
except:
    print("Could not find img_skew_strip.png")
    sys.exit()
    
img_skew_strip = lv.img_dsc_t({
  'data_size': len(png_data),
  'data': png_data 
})

#
# Image styling and offset
#

style = lv.style_t()
style.init()
style.set_bg_color(lv.palette_main(lv.PALETTE.YELLOW))
style.set_bg_opa(lv.OPA.COVER)
style.set_img_recolor_opa(lv.OPA.COVER)
style.set_img_recolor(lv.color_black())

img = lv.img(lv.scr_act())
img.add_style(style, 0)
img.set_src(img_skew_strip)
img.set_size(150, 100)
img.center()

a = lv.anim_t()
a.init()
a.set_var(img)
a.set_values(0, 100)
a.set_time(3000)
a.set_playback_time(500)
a.set_repeat_count(lv.ANIM_REPEAT.INFINITE)
a.set_custom_exec_cb(lambda a,val: ofs_y_anim(img,val))
lv.anim_t.start(a)


API

Functions

lv_obj_t *lv_img_create(lv_obj_t *parent)

Create a image objects

Parameters

parent -- pointer to an object, it will be the parent of the new image

Returns

pointer to the created image

void lv_img_set_src(lv_obj_t *obj, const void *src)

Set the image data to display on the the object

Parameters
  • obj -- pointer to an image object

  • src_img -- 1) pointer to an lv_img_dsc_t descriptor (converted by LVGL's image converter) (e.g. &my_img) or 2) path to an image file (e.g. "S:/dir/img.bin")or 3) a SYMBOL (e.g. LV_SYMBOL_OK)

void lv_img_set_offset_x(lv_obj_t *obj, lv_coord_t x)

Set an offset for the source of an image so the image will be displayed from the new origin.

Parameters
  • obj -- pointer to an image

  • x -- the new offset along x axis.

void lv_img_set_offset_y(lv_obj_t *obj, lv_coord_t y)

Set an offset for the source of an image. so the image will be displayed from the new origin.

Parameters
  • obj -- pointer to an image

  • y -- the new offset along y axis.

void lv_img_set_angle(lv_obj_t *obj, int16_t angle)

Set the rotation angle of the image. The image will be rotated around the set pivot set by lv_img_set_pivot()

Parameters
  • obj -- pointer to an image object

  • angle -- rotation angle in degree with 0.1 degree resolution (0..3600: clock wise)

void lv_img_set_pivot(lv_obj_t *obj, lv_coord_t x, lv_coord_t y)

Set the rotation center of the image. The image will be rotated around this point

Parameters
  • obj -- pointer to an image object

  • x -- rotation center x of the image

  • y -- rotation center y of the image

void lv_img_set_zoom(lv_obj_t *obj, uint16_t zoom)
void lv_img_set_antialias(lv_obj_t *obj, bool antialias)

Enable/disable anti-aliasing for the transformations (rotate, zoom) or not. The qualitiy is better with anti-aliasing looks better but slower.

Parameters
  • obj -- pointer to an image object

  • antialias -- true: anti-aliased; false: not anti-aliased

const void *lv_img_get_src(lv_obj_t *obj)

Get the source of the image

Parameters

obj -- pointer to an image object

Returns

the image source (symbol, file name or ::lv-img_dsc_t for C arrays)

lv_coord_t lv_img_get_offset_x(lv_obj_t *obj)

Get the offset's x attribute of the image object.

Parameters

img -- pointer to an image

Returns

offset X value.

lv_coord_t lv_img_get_offset_y(lv_obj_t *obj)

Get the offset's y attribute of the image object.

Parameters

obj -- pointer to an image

Returns

offset Y value.

uint16_t lv_img_get_angle(lv_obj_t *obj)

Get the rotation angle of the image.

Parameters

obj -- pointer to an image object

Returns

rotation angle in 0.1 degrees (0..3600)

void lv_img_get_pivot(lv_obj_t *obj, lv_point_t *pivot)

Get the pivot (rotation center) of the image.

Parameters
  • img -- pointer to an image object

  • pivot -- store the rotation center here

uint16_t lv_img_get_zoom(lv_obj_t *obj)

Get the zoom factor of the image.

Parameters

obj -- pointer to an image object

Returns

zoom factor (256: no zoom)

bool lv_img_get_antialias(lv_obj_t *obj)

Get whether the transformations (rotate, zoom) are anti-aliased or not

Parameters

obj -- pointer to an image object

Returns

true: anti-aliased; false: not anti-aliased

Variables

const lv_obj_class_t lv_img_class
struct lv_img_t

Public Members

lv_obj_t obj
const void *src
lv_point_t offset
lv_coord_t w
lv_coord_t h
uint16_t angle
lv_point_t pivot
uint16_t zoom
uint8_t src_type
uint8_t cf
uint8_t antialias