Forward DCT (also controls coefficient quantization) A forward DCT routine is given a pointer to an input sample array and a pointer to a work area of type DCTELEM[]; the DCT is to be performed in-place in that buffer. Type DCTELEM is int for 8-bit samples, INT32 for 12-bit samples. (NOTE: Floating-point DCT implementations use an array of type FAST_FLOAT, instead.) The input data is to be fetched from the sample array starting at a specified column. (Any row offset needed will be applied to the array pointer before it is passed to the FDCT code.) Note that the number of samples fetched by the FDCT routine is DCT_h_scaled_size * DCT_v_scaled_size. The DCT outputs are returned scaled up by a factor of 8; they therefore have a range of +-8K for 8-bit data, +-128K for 12-bit data. This convention improves accuracy in integer implementations and saves some work in floating-point ones. Each IDCT routine has its own ideas about the best dct_table element type.
jpeg_forward_dct Class Documentation
Beispiel #1
0
        /// <summary>
        /// Master selection of compression modules.
        /// This is done once at the start of processing an image.  We determine
        /// which modules will be used and give them appropriate initialization calls.
        /// This routine is in charge of selecting the modules to be executed and
        /// making an initialization call to each one.
        /// </summary>
        private void jinit_compress_master()
        {
            /* Initialize master control (includes parameter checking/processing) */
            jinit_c_master_control(false /* full compression */);

            /* Preprocessing */
            if (!m_raw_data_in)
            {
                m_cconvert = new jpeg_color_converter(this);
                m_downsample = new jpeg_downsampler(this);
                m_prep = new jpeg_c_prep_controller(this);
            }

            /* Forward DCT */
            m_fdct = new jpeg_forward_dct(this);

            /* Entropy encoding: only Huffman coding supported. */
            if (m_progressive_mode)
                m_entropy = new phuff_entropy_encoder(this);
            else
                m_entropy = new huff_entropy_encoder(this);

            /* Need a full-image coefficient buffer in any multi-pass mode. */
            m_coef = new my_c_coef_controller(this, (bool)(m_num_scans > 1 || m_optimize_coding));
            jinit_c_main_controller(false /* never need full buffer here */);
            m_marker = new jpeg_marker_writer(this);

            /* Write the datastream header (SOI) immediately.
            * Frame and scan headers are postponed till later.
            * This lets application insert special markers after the SOI.
            */
            m_marker.write_file_header();
        }
Beispiel #2
0
        /// <summary>
        /// Master selection of compression modules.
        /// This is done once at the start of processing an image.  We determine
        /// which modules will be used and give them appropriate initialization calls.
        /// This routine is in charge of selecting the modules to be executed and
        /// making an initialization call to each one.
        /// </summary>
        private void jinit_compress_master()
        {
            /* Sanity check on image dimensions */
            if (m_image_height <= 0 || m_image_width <= 0 || m_input_components <= 0)
                ERREXIT(J_MESSAGE_CODE.JERR_EMPTY_IMAGE);

            /* Initialize master control (includes parameter checking/processing) */
            jinit_c_master_control(false /* full compression */);

            /* Preprocessing */
            if (!m_raw_data_in)
            {
                m_cconvert = new jpeg_color_converter(this);
                m_downsample = new jpeg_downsampler(this);
                m_prep = new jpeg_c_prep_controller(this);
            }

            /* Forward DCT */
            m_fdct = new jpeg_forward_dct(this);

            /* Entropy encoding: either Huffman or arithmetic coding. */
            if (arith_code)
                m_entropy = new arith_entropy_encoder(this);
            else
                m_entropy = new huff_entropy_encoder(this);

            /* Need a full-image coefficient buffer in any multi-pass mode. */
            m_coef = new my_c_coef_controller(this, (bool)(m_num_scans > 1 || m_optimize_coding));
            jinit_c_main_controller(false /* never need full buffer here */);
            m_marker = new jpeg_marker_writer(this);

            /* Write the datastream header (SOI) immediately.
            * Frame and scan headers are postponed till later.
            * This lets application insert special markers after the SOI.
            */
            m_marker.write_file_header();
        }