JPG decoder(JPG解码器)


Allow the use of JPG images in LVGL. Besides that it also allows the use of a custom format, called Split JPG (SJPG), which can be decoded in more optimal way on embedded systems.

JPG解码器让我们可以在 LVGL 中使用 JPG 图像。除此之外,它还允许使用称为拆分 JPG (SJPG) 的自定义格式,这个格式可以在嵌入式系统上以更优化的方式进行解码。



  • Supports both normal JPG and the custom SJPG formats.

  • Decoding normal JPG consumes RAM with the size fo the whole uncompressed image (recommended only for devices with more RAM)

  • SJPG is a custom format based on "normal" JPG and specially made for LVGL.

  • SJPG is 'split-jpeg' which is a bundle of small jpeg fragments with an sjpg header.

  • SJPG size will be almost comparable to the jpg file or might be a slightly larger.

  • File read from file and c-array are implemented.

  • SJPEG frame fragment cache enables fast fetching of lines if available in cache.

  • By default the sjpg image cache will be image width * 2 * 16 bytes (can be modified)

  • Currently only 16 bit image format is supported (TODO)

  • Only the required partion of the JPG and SJPG images are decoded, therefore they can't be zoomed or rotated.

  • 支持普通 JPG 和自定义 SJPG 格式。

  • 解码普通 JPG 会消耗整个未压缩图像大小的 RAM(仅推荐用于具有更多 RAM 的设备)

  • SJPG 是一种基于 “普通” JPG 的自定义格式,非常适合在 LVGL 上使用。

  • SJPG 是 split-jpeg ,它是一段带有 sjpg 标头的小 jpeg 片段数据。

  • SJPG 大小将几乎与 jpg 文件相当,或者可能会稍大一些。

  • 实现了从文件和 c-array 读取文件。

  • 如果在缓存中可用,SJPEG 帧片段缓存可以快速获取行。

  • 默认情况下,sjpg 图像缓存大小为 图像宽度 * 2 * 16 字节(可修改)

  • 目前仅支持 16 位图像格式 (TODO)

  • 仅对 JPG 和 SJP G图像的所需部分进行解码,所以无法缩放或旋转。



If enabled in lv_conf.h by LV_USE_SJPG LVGL will register a new image decoder automatically so JPG and SJPG files can be directly used as image sources. For example:

lv_img_set_src(my_img, "S:path/to/picture.jpg");

Note that, a file system driver needs to registered to open images from files. Read more about it here or just enable one in lv_conf.h with LV_USE_FS_...

如果在 lv_conf.h 中启用了 LV_USE_SJPG ,LVGL 在初始化时会自动注册 jpg 图像解码器,之后 JPG 和 SJPG 文件可以直接用作图像源使用。例如:

lv_img_set_src(my_img, "S:path/to/picture.jpg");

注意,这需要注册文件系统驱动程序才能从文件中打开图像。点击这里阅读了解更多信息,或直接在 lv_conf.h 中打开其中一个类似 LV_USE_FS_... 的宏。


Converting JPG to C array(转换JPG为C数组)


  • Use lvgl online tool

  • Color format = RAW, output format = C Array

Converting JPG to SJPG (转换JPG为SJPG)


python3 and the PIL library required. (PIL can be installed with pip3 install pillow)

To create SJPG from JPG:

  • Copy the image to convert into lvgl/scripts

  • cd lvgl/scripts

  • python3 image_to_convert.jpg. It creates both a C files and an SJPG image.

The expected result is:

Conversion started...

        RES = 640 x 480

        Time taken = 1.66 sec
        bin size = 77.1 KB
        walpaper.sjpg           (bin file)
        walpaper.c              (c array)

All good!

需要 python3 和 PIL 库。 (PIL可以用pip安装 pip3 install pillow )

通过 jpg 生成 SJPG:

  • 复制jpg图像文件到 lvgl/scripts 目录下

  • 进入到 lvgl/scripts 目录: cd lvgl/scripts

  • 执行脚本转换脚本,注意,这会同时创建一个 C 文件和一个 SJPG 图像: python3 image_to_convert.jpg


Conversion started...

        RES = 640 x 480

        Time taken = 1.66 sec
        bin size = 77.1 KB
        walpaper.sjpg           (bin file)
        walpaper.c              (c array)

All good!



Load an SJPG image

C code  

#include "../../lv_examples.h"

 * Load an SJPG image
void lv_example_sjpg_1(void)
  lv_obj_t * wp;

  wp = lv_img_create(lv_scr_act());
  /* Assuming a File system is attached to letter 'A'
   * E.g. set LV_USE_FS_STDIO 'A' in lv_conf.h */
  lv_img_set_src(wp, "A:lvgl/examples/libs/sjpg/small_image.sjpg");


MicroPython code  

 GitHub Simulator
#!/opt/bin/lv_micropython -i
import lvgl as lv
import display_driver
import fs_driver

fs_drv = lv.fs_drv_t()
fs_driver.fs_register(fs_drv, 'S')

wp = lv.img(lv.scr_act())
# The File system is attached to letter 'S'




void lv_split_jpeg_init(void)