JPG decoder(JPG解码器)¶

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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 decided in more optimal way on embedded systems.

允许在 LVGL 中使用 JPG 图像。除此之外，它还允许使用称为 Split JPG (SJPG) 的自定义格式，可以在嵌入式系统上以更优化的方式决定。

Overview(概述)¶

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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 availble 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 是基于“普通”JPG 的自定义格式，专为LVGL。
SJPG 是“split-jpeg”，它是一捆带有 sjpg 标头的小 jpeg 片段。
SJPG 大小几乎与 jpg 文件相当，或者可能稍大一些。
从文件和 c-array 读取的文件已实现。
如果缓存中可用，SJPEG 帧片段缓存可以快速获取行。
默认情况下，sjpg 图像缓存将为图像宽度 * 2 * 16 字节（可以修改）- 目前仅支持 16 位图像格式（TODO )
仅解码 JPG 和 SJPG 图像所需的部分，因此无法对其进行缩放或旋转。

Usage(用法)¶

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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:

如果在 lv_conf.h 中通过 LV_USE_SJPG 启用 LVGL 将自动注册一个新的图像解码器，因此 JPG 和 SJPG 文件可以直接用作图像源。例如：

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

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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_...

请注意，文件系统驱动程序需要注册才能从文件中打开图像。阅读更多相关信息此处或仅在 lv_conf.h 中使用 LV_USE_FS_... 启用一个

Converter(转换器)¶

Converting JPG to C array(将 JPG 转换为 C 数组)¶

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Use lvgl online tool https://lvgl.io/tools/imageconverter
Color format = RAW, output format = C Array

使用 lvgl 在线工具 https://lvgl.io/tools/imageconverter
颜色格式 = RAW，输出格式 = C 数组

Converting JPG to SJPG(将 JPG 转换为 SJPG)¶

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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 jpg_to_sjpg.py image_to_convert.jpg. It creates both a C files and an SJPG image.

The expected result is:

Conversion started...

Input:
        image_to_convert.jpg
        RES = 640 x 480

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

All good!

Example(示例)¶

API¶

Functions

void lv_split_jpeg_init(void)¶