jpeg_gray.h File Reference

Decodes a QVGA camera JPEG at 1/8 scale straight into the 40x30 gray grid the tracker uses. More...

#include "tracking_types.h"
#include <cstddef>
#include <cstdint>

Go to the source code of this file.

Functions
bool	jpeg_gray::decode (const uint8_t *jpeg, size_t len, tracking::GrayFrame &out)
	false if the JPEG is corrupt or its 1/8-scale size is not 40x30 (frame size must be QVGA).

Detailed Description

Decodes a QVGA camera JPEG at 1/8 scale straight into the 40x30 gray grid the tracker uses.

Uses the vendored C TJpgDec (lib/tjpgd). At 1/8 scale the decoder keeps only each 8x8 block's DC coefficient (the block average) and skips the IDCT entirely (1/2 and 1/4 run the full IDCT and then average, ~71 ms at 1/4). The block average also filters noise. The ESP32 ROM has the same decoder, but it is ~40% slower (Stage 7: 14.1 ms vs 9.0 ms for one 4.1 KB frame on core 3), so it is not used. No allocation; NOT re-entrant (the decoder's work buffer is static), so only the detection task may call it.