Reading Image Metadata¶

Jetraw-compressed buffers carry the image dimensions and the sensor parameters that were used during preparation. Prepared (or decompressed) images carry the sensor parameters embedded in the pixel data. Jetraw Standalone can read this metadata back without external bookkeeping.

Reading dimensions from a compressed buffer¶

The dimensions of a compressed image can be read directly from the buffer, which allows allocating the output buffer before decoding:

#include "jetraw_standalone.h"
#include <cstdint>
#include <iostream>
#include <vector>

int main() {
    const char* compressed = /* ... */;
    size_t compressed_size = /* ... */;

    uint32_t width = 0;
    uint32_t height = 0;
    dp_status status = jetraw_read_encoded_dimensions(
        compressed, compressed_size, &width, &height);
    if (status != dp_success) {
        std::cerr << "Error: " << dp_status_description(status) << '\n';
        return 1;
    }

    std::cout << "Image is " << width << " x " << height << " pixels\n";

    std::vector<uint16_t> image(width * height);
    jetraw_decode(compressed, static_cast<int32_t>(compressed_size),
                  image.data(), width * height);
}

Reading sensor parameters from a compressed buffer¶

The EMVA 1288 sensor parameters can be extracted directly from a compressed bitstream, without decoding it first:

#include "jetraw_standalone.h"
#include <iostream>

int main() {
    const char* compressed = /* ... */;
    size_t compressed_size = /* ... */;

    JetrawEMVAParameters params;
    dp_status status = jetraw_read_encoded_emva_params(
        compressed, compressed_size, &params);
    if (status != dp_success) {
        std::cerr << "Error: " << dp_status_description(status) << '\n';
        return 1;
    }

    std::cout << "gain: " << params.gain << " DN/e-, "
              << "black level: " << params.black_level << " DN\n";
}

Reading sensor parameters from an image buffer¶

The same parameters can be extracted from a raw 16-bit image buffer that was processed by dpcore_prepare_image / dpcore_embed_meta, or that was decompressed with Jetraw:

#include "jetraw_standalone.h"
#include <cstdint>
#include <iostream>

int main() {
    const uint16_t* image = /* prepared or decompressed image */;
    size_t num_pixels = /* ... */;

    JetrawEMVAParameters params;
    dp_status status = jetraw_read_emva_params(image, num_pixels, &params);
    if (status == dp_bad_image) {
        std::cerr << "No embedded parameters found - "
                     "was the image prepared?\n";
        return 1;
    }
}

Notes¶

jetraw_read_emva_params expects a single frame; pass the number of pixels (not bytes).
Reading parameters from an unprepared image fails with dp_bad_image.

See Also¶