WriteJPGBuffer method using libjpeg libraries instead of ijl15.lib - c++

Question

We have following method implemented using ijl15.lib API.
We want to use libjpeg libraries instead of ijl. How should I implement WriteJPGBuffer using libjpeg libraries? We are aware of LoadJPG and SaveJPG from file. However i want to write and read the jpg image in buffer using libjpeg libraries. Any inputs will be very helpul. Thank you in advance.
unsigned char WriteJPGBuffer(unsigned int &size)
{
size = 0;
int jErr;
JPEG_CORE_PROPERTIES jpgProps;
bool colorsSwapped;
if (!jpgSupported)
return NULL;
jErr = ijlInit(&jpgProps);
if (jErr != IJL_OK)
return NULL;
jpgProps.DIBWidth = m_width;
jpgProps.DIBHeight = -m_height;
jpgProps.DIBBytes = (unsigned char *)m_pData;
jpgProps.DIBPadBytes = 0 ;
jpgProps.DIBChannels = 4;
jpgProps.DIBColor = IJL_RGB;
jpgProps.JPGFile = NULL;
jpgProps.JPGWidth = m_width;
jpgProps.JPGHeight = m_height;
jpgProps.JPGChannels = 3;
jpgProps.JPGColor = IJL_YCBCR;
jpgProps.JPGSubsampling = IJL_411;
jpgProps.jquality = jpgQuality;
unsigned int iSize = m_width*m_height*3;
unsigned char * pBuffer = new unsigned char[iSize];
jpgProps.JPGSizeBytes = iSize;
jpgProps.JPGBytes = pBuffer;
jpgProps.jprops.jpeg_comment_size = (unsigned short)m_strCommentAdobe.length;
jpgProps.jprops.jpeg_comment = (char*)m_strCommentAdobe;
colorsSwapped = SetInternalFormat(RGB);
jErr = ijlWrite(&jpgProps, IJL_JBUFF_WRITEWHOLEIMAGE);
if (colorsSwapped)
SetInternalFormat(BGR);
if (jErr != IJL_OK)
{
ijlFree(&jpgProps);
return NULL;
}
size = jpgProps.JPGSizeBytes;
ijlFree(&jpgProps);
return jpgProps.JPGBytes;
}

Answer 1

Thanks for your inputs. I have implemented the solution below through RND. In below implementation, we have image data stored in the class member variable in the form of RGBQUAD which i am converting into unsigned char* first using ConversionfromGLRGBQUADToUnsignedChar function and then writing it jpeg buffer.
void ConversionfromGLRGBQUADToUnsignedChar(unsigned char* dataInCharFromGLRGBQUAD)
{
int spot,spotDst;
for (int y = 0;y < m_height;y++)
{
for (int x = 0;x<m_width;x++)
{
spot = y * m_width + x;
spotDst = spot * 3;
dataInCharFromGLRGBQUAD[spotDst] = m_pData[spot].red;
dataInCharFromGLRGBQUAD[spotDst + 1] = m_pData[spot].green;
dataInCharFromGLRGBQUAD[spotDst + 2] = m_pData[spot].blue;
}
}
}
unsigned char * WriteJPGBuffer(unsigned int &size)
{
size = 0;
struct jpeg_compress_struct cinfo;
struct jpeg_error_mgr jerr;
JSAMPROW row_pointer[1];
unsigned char* dataInCharFromGLRGBQUAD;
bool colorsSwapped;
int row_stride;
cinfo.err = jpeg_std_error(&jerr);
jpeg_create_compress(&cinfo);
unsigned long sizeOfJPGBuffer = 0;
jpeg_mem_dest(&cinfo, &m_pDIBData, &sizeOfJPGBuffer);
cinfo.image_width = m_width;
cinfo.image_height = m_height;
cinfo.input_components = 3;
cinfo.in_color_space = JCS_RGB;
cinfo.jpeg_color_space = JCS_YCbCr;
jpeg_set_defaults(&cinfo);
jpeg_set_quality(&cinfo, jpgQuality, true);
jpeg_start_compress(&cinfo, true);
colorsSwapped = SetInternalFormat(RGB);
FlipVert();
dataInCharFromGLRGBQUAD = new unsigned char[m_width*m_height*3];
ConversionfromGLRGBQUADToUnsignedChar(dataInCharFromGLRGBQUAD);
row_stride = cinfo.image_width * cinfo.input_components;
while (cinfo.next_scanline < cinfo.image_height)
{
row_pointer[0] = &dataInCharFromGLRGBQUAD[cinfo.next_scanline * row_stride];
jpeg_write_scanlines(&cinfo, row_pointer, 1);
}
if (colorsSwapped)
SetInternalFormat(BGR);
jpeg_finish_compress(&cinfo);
jpeg_destroy_compress(&cinfo);
size = sizeOfJPGBuffer;
delete[] dataInCharFromGLRGBQUAD;
return m_pDIBData;
}