Method preprocess_image

src/common/AutoModel/modeling_gemma3_image.cpp:60–88

@brief: preprocess the image for gemma3 model @note: 1. Reorder: 896x896x3 -> 3x896x896 @param: image: the image to preprocess @return: the preprocessed image

///@param: image: the image to preprocess
///@return: the preprocessed image
buffer<bf16> Gemma3::preprocess_image(bytes& image) {
    buffer<bf16> result(3 * 896 * 896);
    const int total_pixels = 896 * 896;
    image_data_t input;
    input.width = 896;
    input.height = 896;
    input.pixels = image;

    image_data_t chw;
    if (!image_reader_.reorder_hwc_to_chw(input, chw) || chw.pixels.size() < static_cast<size_t>(total_pixels) * 3) {
        image.release();
        return result;
    }

    const uint8_t* src = chw.pixels.data();
    const float scale = 1.0f / 255.0f;

    for (int c = 0; c < 3; ++c) {
        const size_t channel_offset = static_cast<size_t>(c) * total_pixels;
        for (int i = 0; i < total_pixels; ++i) {
            float normalized = (static_cast<float>(src[channel_offset + i]) * scale - 0.5f) * 2.0f;
            result[channel_offset + i] = bf16(normalized);
        }
    }

    image_reader_.recycle(chw);
    image.release();
    return result;
}