12.1. JPEG decode

12.1.1. Overview

JPEG decoding example project demonstrates how to decode a JPG file using either JPEG module or software jpeg library

12.1.2. Board Setting

  • Connect the USB disk to the development board usb0, or insert the SD memory card into the development board SD card

  • Connect LCD screen to development board

12.1.3. Configuration

  • File CMakeLists.txt.

    • set (JPEG_USE_SDCARD 1) to read jpeg file (.jpg) from SD card or set (JPEG_USE_UDISK 1) to read jpeg file (.jpg) from u-disk. These options are exclusive.

    • set (JPEG_HW_MODE 1) to decode jpeg file with JPEG module; set (JPEG_HW_MODE 0) to decode with software library

12.1.4. Supported picture formats

  • Supports standard JPEG images： JPEG picture format components：SOI（File header）+APP0（Image identification information）+ DQT（Define quantification table）+ SOF0（Basic image information）+ DHT（Define Huffman table） + DRI（Define restart interval）+ SOS（Scan line start）+ EOI（End of document），the SOI is composed of two hexadecimal bytes (ffd8)。

  • The sampling factor supported by the JPEG picture is：YUV420、YUV422H、YUV422V、YUV444、YUV400，Such as a JPG image in 800 * 400 YUV420 format，Through the worm EXIF viewerGraphic insect EXIF viewer official websiteavailable： FileType JPEG FileTypeExtension jpg MIMEType image/jpeg ImageWidth 800 ImageHeight 480 EncodingProcess Baseline DCT, Huffman coding BitsPerSample 8 ColorComponents 3 YCbCrSubSampling YCbCr4:2:0 (2 2)

12.1.5. Image size and resolution supported by this routine

  • jpeg file size is expected to be less than 500KB, image resolution is expected to be less than 1024 * 768, defined in common/inc/file_op.h

12.1.6. Running the example

  • Configure storage in CMakeLists.txt

  • Put jpeg files (with .jpg) into target storage

  • Connect LCD pannel and storage to board

  • Power on the board

  • Download built elf into development board and run the demo

  • If everything goes well, jpeg files stored in the target storage will be show on LCD pannel one by one.