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97 lines
2.4 KiB
ReStructuredText
97 lines
2.4 KiB
ReStructuredText
===========
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JPG decoder
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===========
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Allow the use of JPG images in LVGL. Besides that it also allows the use
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of a custom format, called Split JPG (SJPG), which can be decoded in
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more optimal way on embedded systems.
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Overview
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--------
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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
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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
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LVGL.
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- SJPG is ‘split-jpeg’ which is a bundle of small jpeg fragments with
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an sjpg header.
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- SJPG size will be almost comparable to the jpg file or might be a
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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
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available in cache.
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- By default the sjpg image cache will be image width \* 2 \* 16 bytes
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(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,
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therefore they can’t be zoomed or rotated.
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Usage
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-----
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If enabled in ``lv_conf.h`` by :c:macro:`LV_USE_SJPG` LVGL will register a new
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image decoder automatically so JPG and SJPG files can be directly used
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as image sources. For example:
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.. code:: c
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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
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files. Read more about it :ref:`file-system` or just
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enable one in ``lv_conf.h`` with ``LV_USE_FS_...``
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Converter
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---------
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Converting JPG to C array
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~~~~~~~~~~~~~~~~~~~~~~~~~
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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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~~~~~~~~~~~~~~~~~~~~~~
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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: - Copy the image to convert into
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``lvgl/scripts`` - ``cd lvgl/scripts`` -
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``python3 jpg_to_sjpg.py image_to_convert.jpg``. It creates both a C
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files and an SJPG image.
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The expected result is:
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.. code:: 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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Example
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-------
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.. include:: ../examples/libs/sjpg/index.rst
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API
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---
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:ref:`lv_sjpg`
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:ref:`tjpgd`
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:ref:`tjpgdcnf`
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