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74 lines
2.3 KiB
Markdown
74 lines
2.3 KiB
Markdown
2 years ago
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# JPG decoder
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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 decoded in more optimal way on embedded systems.
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## Overview
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- Supports both normal JPG and the custom SJPG formats.
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- Decoding normal JPG consumes RAM with the size fo the whole uncompressed image (recommended only for devices with more RAM)
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- SJPG is a custom format based on "normal" JPG and specially made for LVGL.
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- SJPG is 'split-jpeg' which is a bundle of small jpeg fragments with an sjpg header.
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- SJPG size will be almost comparable to the jpg file or might be a slightly larger.
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- File read from file and c-array are implemented.
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- SJPEG frame fragment cache enables fast fetching of lines if available in cache.
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- By default the sjpg image cache will be image width * 2 * 16 bytes (can be modified)
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- Currently only 16 bit image format is supported (TODO)
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- Only the required partion of the JPG and SJPG images are decoded, therefore they can't be zoomed or rotated.
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## Usage
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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:
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```
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lv_img_set_src(my_img, "S:path/to/picture.jpg");
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```
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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_...`
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## Converter
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### Converting JPG to C array
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- Use lvgl online tool https://lvgl.io/tools/imageconverter
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- Color format = RAW, output format = C Array
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### Converting JPG to SJPG
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python3 and the PIL library required. (PIL can be installed with `pip3 install pillow`)
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To create SJPG from JPG:
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- Copy the image to convert into `lvgl/scripts`
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- `cd lvgl/scripts`
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- `python3 jpg_to_sjpg.py image_to_convert.jpg`. It creates both a C files and an SJPG image.
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The expected result is:
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```sh
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Conversion started...
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Input:
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image_to_convert.jpg
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RES = 640 x 480
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Output:
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Time taken = 1.66 sec
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bin size = 77.1 KB
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walpaper.sjpg (bin file)
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walpaper.c (c array)
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All good!
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```
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## Example
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```eval_rst
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.. include:: ../../examples/libs/sjpg/index.rst
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```
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## API
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```eval_rst
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.. doxygenfile:: lv_sjpg.h
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:project: lvgl
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