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README.md

Supported Targets ESP32-P4 ESP32-S31

JPEG decode example

Overview

This example demonstrates how to use the JPEG hardware decoder to decode one embedded JPEG image into RGB888 raw bytes in default BGR24 order.

The example performs:

  • Embedding main/assets/image.jpg into the application image
  • Letting the JPEG decoder read the embedded JPEG bitstream directly from flash
  • Parsing the JPEG header with jpeg_decoder_get_info()
  • Decoding the image into an RGB888 output buffer with default BGR24 byte order
  • Allocating the output buffer for padded dimensions when the JPEG block layout rounds width or height up to 16-pixel boundaries
  • Base64-encoding the decoded raw pixels and printing them with machine-parseable UART markers
  • Letting pytest rebuild jpeg_decode_result.ppm for inspection and compare it against golden_output.ppm

Hardware Required

Any board based on a supported target can be used. No SD card or external storage setup is required.

Build and Flash

Run idf.py -p PORT flash monitor to build, flash and monitor the project.

(To exit the serial monitor, type Ctrl-].)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

Example Output

Loading embedded JPEG from flash...
Embedded JPEG size: 43700 bytes
JPEG header parsed: width=320 height=240
Decoding JPEG -> RGB888...
Decoded RGB888 size: 245760 bytes
JPEG_DECODE_INFO width=320 height=240 padded_width=320 padded_height=256 format=RGB888 encoding=base64 size=245760
JPEG_DECODE_BASE64_BEGIN
JPEG_DECODE_BASE64 ...
JPEG_DECODE_BASE64 ...
JPEG_DECODE_BASE64_END
JPEG decode demo done.

padded_width and padded_height report the actual decoded buffer dimensions. For JPEGs whose block layout pads the output to 16-pixel boundaries, these values can be larger than the visible width and height, so the output buffer must be sized for the padded image.

Pytest Regression Check

The accompanying pytest_jpeg_decode.py script waits for the JPEG_DECODE_INFO and JPEG_DECODE_BASE64 markers, reconstructs the decoded raw pixel output, crops away padded rows, and saves the visible image as:

  • dut.logdir/jpeg_decode_result.ppm

The test writes the PPM file and compares it with golden_output.ppm. This makes the example both a functional regression test and a host-side artifact generator for inspection.

Running Pytest Locally And Viewing The Image

To run the pytest helper locally on hardware, build the example for your target first, then invoke the test script with the target and serial port:

idf.py set-target esp32p4 build
pytest --target esp32p4 --port PORT pytest_jpeg_decode.py

Replace esp32p4 with another supported target such as esp32s31 when needed.

pytest-embedded stores per-test logs under $IDF_PATH/pytest-embedded/. The script writes the reconstructed image to jpeg_decode_result.ppm inside that test log directory, so after the test finishes you can open the generated PPM file locally with an image viewer that supports PPM to inspect the decoded output.

Replacing The Embedded JPEG Asset

If you want to try another input image, replace:

  • main/assets/image.jpg

Keep the replacement as a baseline JPEG with the same general scale if you want UART log volume and test runtime to stay small.

After replacing the asset, rerun the example and update golden_output.ppm from the generated dut.logdir/jpeg_decode_result.ppm artifact if the new output should become the expected result.

Troubleshooting

(For any technical queries, please open an issue on GitHub. We will get back to you as soon as possible.)