// Set up the scan parameters for the current scan
private void select_scan_parameters()
{
if (m_cinfo.m_scan_info != null)
{
/* Prepare for current scan --- the script is already validated */
jpeg_scan_info scanInfo = m_cinfo.m_scan_info[m_scan_number];
m_cinfo.m_comps_in_scan = scanInfo.comps_in_scan;
for (int ci = 0; ci < scanInfo.comps_in_scan; ci++)
{
m_cinfo.m_cur_comp_info[ci] = scanInfo.component_index[ci];
}
if (m_cinfo.m_progressive_mode)
{
m_cinfo.m_Ss = scanInfo.Ss;
m_cinfo.m_Se = scanInfo.Se;
m_cinfo.m_Ah = scanInfo.Ah;
m_cinfo.m_Al = scanInfo.Al;
return;
}
}
else
{
/* Prepare for single sequential-JPEG scan containing all components */
if (m_cinfo.m_num_components > JpegConstants.MAX_COMPS_IN_SCAN)
{
m_cinfo.ERREXIT(J_MESSAGE_CODE.JERR_COMPONENT_COUNT, m_cinfo.m_num_components, JpegConstants.MAX_COMPS_IN_SCAN);
}
m_cinfo.m_comps_in_scan = m_cinfo.m_num_components;
for (int ci = 0; ci < m_cinfo.m_num_components; ci++)
{
m_cinfo.m_cur_comp_info[ci] = ci;
}
}
m_cinfo.m_Ss = 0;
m_cinfo.m_Se = m_cinfo.block_size * m_cinfo.block_size - 1;
m_cinfo.m_Ah = 0;
m_cinfo.m_Al = 0;
}
/// <summary>
/// Generates a default scan script for writing a progressive-JPEG file.
/// </summary>
/// <remarks>This is the recommended method of creating a progressive file, unless you want
/// to make a custom scan sequence. You must ensure that the JPEG color space is
/// set correctly before calling this routine.</remarks>
/// <seealso href="ce3f6712-3633-4a58-af07-626a4fba9ae4.htm" target="_self">Compression parameter selection</seealso>
public void jpeg_simple_progression()
{
/* Safety check to ensure start_compress not called yet. */
if (m_global_state != JpegState.CSTATE_START)
ERREXIT(J_MESSAGE_CODE.JERR_BAD_STATE, (int)m_global_state);
/* Figure space needed for script. Calculation must match code below! */
int nscans;
if (m_num_components == 3 && m_jpeg_color_space == J_COLOR_SPACE.JCS_YCbCr)
{
/* Custom script for YCbCr color images. */
nscans = 10;
}
else
{
/* All-purpose script for other color spaces. */
if (m_num_components > JpegConstants.MAX_COMPS_IN_SCAN)
{
/* 2 DC + 4 AC scans per component */
nscans = 6 * m_num_components;
}
else
{
/* 2 DC scans; 4 AC scans per component */
nscans = 2 + 4 * m_num_components;
}
}
/* Allocate space for script.
* We need to put it in the permanent pool in case the application performs
* multiple compressions without changing the settings. To avoid a memory
* leak if jpeg_simple_progression is called repeatedly for the same JPEG
* object, we try to re-use previously allocated space, and we allocate
* enough space to handle YCbCr even if initially asked for grayscale.
*/
if (m_script_space == null || m_script_space_size < nscans)
{
m_script_space_size = Math.Max(nscans, 10);
m_script_space = new jpeg_scan_info[m_script_space_size];
for (int i = 0; i < m_script_space_size; i++)
m_script_space[i] = new jpeg_scan_info();
}
m_scan_info = m_script_space;
m_num_scans = nscans;
int scanIndex = 0;
if (m_num_components == 3 && m_jpeg_color_space == J_COLOR_SPACE.JCS_YCbCr)
{
/* Custom script for YCbCr color images. */
/* Initial DC scan */
fill_dc_scans(ref scanIndex, m_num_components, 0, 1);
/* Initial AC scan: get some luma data out in a hurry */
fill_a_scan(ref scanIndex, 0, 1, 5, 0, 2);
/* Chroma data is too small to be worth expending many scans on */
fill_a_scan(ref scanIndex, 2, 1, 63, 0, 1);
fill_a_scan(ref scanIndex, 1, 1, 63, 0, 1);
/* Complete spectral selection for luma AC */
fill_a_scan(ref scanIndex, 0, 6, 63, 0, 2);
/* Refine next bit of luma AC */
fill_a_scan(ref scanIndex, 0, 1, 63, 2, 1);
/* Finish DC successive approximation */
fill_dc_scans(ref scanIndex, m_num_components, 1, 0);
/* Finish AC successive approximation */
fill_a_scan(ref scanIndex, 2, 1, 63, 1, 0);
fill_a_scan(ref scanIndex, 1, 1, 63, 1, 0);
/* Luma bottom bit comes last since it's usually largest scan */
fill_a_scan(ref scanIndex, 0, 1, 63, 1, 0);
}
else
{
/* All-purpose script for other color spaces. */
/* Successive approximation first pass */
fill_dc_scans(ref scanIndex, m_num_components, 0, 1);
fill_scans(ref scanIndex, m_num_components, 1, 5, 0, 2);
fill_scans(ref scanIndex, m_num_components, 6, 63, 0, 2);
/* Successive approximation second pass */
fill_scans(ref scanIndex, m_num_components, 1, 63, 2, 1);
/* Successive approximation final pass */
fill_dc_scans(ref scanIndex, m_num_components, 1, 0);
fill_scans(ref scanIndex, m_num_components, 1, 63, 1, 0);
}
}