acid-drop

- Hacking the planet from a LilyGo T-Deck using custom firmware
git clone git://git.acid.vegas/acid-drop.git
sjpg.md (2474B)
      1 ```eval_rst
      2 .. include:: /header.rst
      3 :github_url: |github_link_base|/libs/sjpg.md
      4 ```
      5 
      6 # JPG decoder
      7 
      8 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.
      9 
     10 ## Overview
     11   - Supports both normal JPG and the custom SJPG formats.
     12   - Decoding normal JPG consumes RAM with the size fo the whole uncompressed image (recommended only for devices with more RAM)
     13   - SJPG is a custom format based on "normal" JPG and specially made for LVGL.
     14   - SJPG is 'split-jpeg' which is a bundle of small jpeg fragments with an sjpg header.
     15   - SJPG size will be almost comparable to the jpg file or might be a slightly larger.
     16   - File read from file and c-array are implemented.
     17   - SJPEG frame fragment cache enables fast fetching of lines if available in cache.
     18   - By default the sjpg image cache will be image width * 2 * 16 bytes (can be modified)
     19   - Currently only 16 bit image format is supported (TODO)
     20   - Only the required partion of the JPG and SJPG images are decoded, therefore they can't be zoomed or rotated.
     21 
     22 ## Usage
     23 
     24 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:
     25 ```
     26 lv_img_set_src(my_img, "S:path/to/picture.jpg");
     27 ```
     28 
     29 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_...`
     30 
     31 
     32 
     33 ## Converter
     34 
     35 ### Converting JPG to C array
     36   - Use lvgl online tool https://lvgl.io/tools/imageconverter
     37   - Color format = RAW, output format = C Array
     38 
     39 ### Converting JPG to SJPG
     40 python3 and the PIL library required. (PIL can be installed with `pip3 install pillow`)
     41 
     42 To create SJPG from JPG:
     43 - Copy the image to convert into `lvgl/scripts`
     44 - `cd lvgl/scripts`
     45 - `python3 jpg_to_sjpg.py image_to_convert.jpg`. It creates both a C files and an SJPG image.
     46 
     47 The expected result is:
     48 ```sh
     49 Conversion started...
     50 
     51 Input:
     52         image_to_convert.jpg
     53         RES = 640 x 480
     54 
     55 Output:
     56         Time taken = 1.66 sec
     57         bin size = 77.1 KB
     58         walpaper.sjpg           (bin file)
     59         walpaper.c              (c array)
     60 
     61 All good!
     62 ```
     63 
     64 
     65 ## Example
     66 ```eval_rst
     67 
     68 .. include:: ../../examples/libs/sjpg/index.rst
     69 
     70 ```
     71 
     72 ## API
     73 
     74 ```eval_rst
     75 
     76 .. doxygenfile:: lv_sjpg.h
     77   :project: lvgl