bool ImageReaderJPEG::beginReadInternal()

in imagecore/formats/internal/jpeg.cpp [294:378]
68 lines of code
22 McCabe index (conditional complexity)

bool ImageReaderJPEG::beginReadInternal(unsigned int destWidth, unsigned int destHeight, EImageColorModel destColorModel)
{
	J_COLOR_SPACE outputColorSpace = destColorModel == kColorModel_YUV_420 ? JCS_YCbCr : (HAVE_RGBX ? JCS_EXT_RGBX : JCS_RGB);

#if IMAGECORE_WITH_LCMS
	if( m_RawColorProfileSize > 0 && (m_ReadOptions & kReadOption_ApplyColorProfile) != 0 && Image::colorModelIsRGBA(destColorModel) ) {
		m_ColorProfile = cmsOpenProfileFromMem(m_RawColorProfile, m_RawColorProfileSize);
		m_IgnoreColorProfile = true;
		if( m_ColorProfile != NULL ) {
			// Ignore mismatched color profiles.
			if( m_JPEGDecompress.jpeg_color_space != JCS_GRAYSCALE || cmsGetColorSpace(m_ColorProfile) == cmsSigGrayData ) {
				m_sRGBProfile = cmsCreate_sRGBProfile();
				if( m_sRGBProfile == NULL) {
					fprintf(stderr, "error: unable to allocate sRGB profile\n");
					return false;
				}

				unsigned int inputFormat = getLCMSInputFormat(m_JPEGDecompress.jpeg_color_space, m_JPEGDecompress.saw_Adobe_marker);
				m_ColorTransform = cmsCreateTransform(m_ColorProfile, inputFormat, m_sRGBProfile, HAVE_RGBX ? TYPE_RGBA_8 : TYPE_RGB_8, INTENT_PERCEPTUAL, 0);
				if( m_ColorTransform == NULL ) {
					fprintf(stderr, "error: unable to create ICC transform\n");
					return false;
				}

				if( m_JPEGDecompress.jpeg_color_space == JCS_GRAYSCALE ) {
					outputColorSpace = JCS_GRAYSCALE;
				} else if( m_JPEGDecompress.jpeg_color_space == JCS_YCCK || m_JPEGDecompress.jpeg_color_space == JCS_CMYK ) {
					outputColorSpace = JCS_CMYK;
				}

				m_IgnoreColorProfile = false;
			}
		}
	}
#endif

	m_JPEGDecompress.out_color_space = outputColorSpace;
	m_JPEGDecompress.scale_num = 1;
	m_JPEGDecompress.scale_denom = (unsigned int)roundf((float)m_Width / (float)destWidth);
	// This is the default.
	m_JPEGDecompress.dct_method = JDCT_ISLOW;

	if( (m_ReadOptions & kReadOption_DecompressQualityFast) != 0) {
		m_JPEGDecompress.do_fancy_upsampling = FALSE;
		m_JPEGDecompress.dct_method = JDCT_FASTEST;
		m_JPEGDecompress.do_block_smoothing = FALSE;
	}

	if( destColorModel == kColorModel_YUV_420 ) {
		m_JPEGDecompress.raw_data_out = TRUE;
	}

	if( setjmp(m_JPEGError.jmp) ) {
		fprintf(stderr, "error reading JPEG data: %s\n", s_JPEGLastError);
		jpeg_abort_decompress(&m_JPEGDecompress);
		return false;
	}

	jpeg_start_decompress(&m_JPEGDecompress);

	if( destColorModel == kColorModel_YUV_420 ) {
		// Make sure libjpeg doesn't try to upsample the UV components, we need them at half the resolution of Y.
		// Recompute all of the scaling parameters jpeg_start_decompress configured.
		for (int i = 1; i < 3; i++) {
			m_JPEGDecompress.comp_info[i]._DCT_h_scaled_size = m_JPEGDecompress.comp_info[0]._DCT_h_scaled_size;
			m_JPEGDecompress.comp_info[i]._DCT_v_scaled_size = m_JPEGDecompress.comp_info[0]._DCT_v_scaled_size;
			m_JPEGDecompress.comp_info[i].MCU_sample_width = m_JPEGDecompress.comp_info[0].MCU_sample_width / 2;
			m_JPEGDecompress.comp_info[i].downsampled_width = m_JPEGDecompress.comp_info[i].downsampled_width / 2;
			m_JPEGDecompress.comp_info[i].downsampled_height = m_JPEGDecompress.comp_info[i].downsampled_height / 2;
		}
		// Re-trigger the dct method and table calculations.
		int oldState = m_JPEGDecompress.global_state;
		m_JPEGDecompress.global_state = 207;
		jpeg_start_output(&m_JPEGDecompress, 1);
		m_JPEGDecompress.global_state = oldState;
	}

	if( m_JPEGDecompress.output_width != destWidth || m_JPEGDecompress.output_height != destHeight ) {
		fprintf(stderr, "JPEG scaled size mismatch");
		jpeg_abort_decompress(&m_JPEGDecompress);
		return false;
	}

	return true;
}