Tabelas DCT do Extrato JPEG

Question

Eu estou desenvolvendo um visualizador de imagens / editor usando VS2008, MFC e WIC e gostaria de recomprimir JPEGs como estreitamente (wize de qualidade) quanto possível para o seu processamento original, após a imagem.Alguém sabe como extrair tabelas de luminância e crominância para definir http://msdn.microsoft.com/pt-Us / biblioteca / gg430026% 28V= vs.85% 29.aspx sem ter que usar uma biblioteca grande adicional (como libjpeg)?

Answer 1

The JPEG standard specification covers the details of the luminance and chrominance table.

In JPEG terminology, those tables are both referred to as "quantization table" (DQT). The luminance quantization table is applied on the "Y" channel and the chrominance quantization table is applied to "Cb" and "Cr" channels.

This website lists the quantization tables for a large number of camera manufacturers and JPEG authoring software.

To recompress an image using the same quantization tables as another existing image:

• Query and enumerate all IWICMetadataBlockReader objects from the source image (IWICBitmapFrameDecode).
• Find the metadata blocks which have the types GUID_MetadataFormatJpegChrominance and GUID_MetadataFormatJpegLuminance
• Extract their binary data, and use those data to initialize the Luminance and Chrominance properties of the JPEG encoder options by putting them into the IPropertyBag when calling IWICBitmapFrameEncode::Initialize.