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.
## Overview
- 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.
## Usage
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](https://docs.lvgl.io/master/overview/file-system.html) or just enable one in `lv_conf.h` with `LV_USE_FS_...`
## Converter
### Converting JPG to C array
- Use lvgl online tool https://lvgl.io/tools/imageconverter
- Color format = RAW, output format = C Array
### Converting JPG to 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 jpg_to_sjpg.py image_to_convert.jpg`. It creates both a C files and an SJPG image.
