JPEGエキスDCTテーブル

Question

VS2008、MFC、WICを使用して画像ビューアー/エディタを開発しています。画像処理後に、厳密に（品質ウェイズ）のように（品質雑音）を元のものに再圧縮したいと思います。誰もが輝度とクロミナンス表を抽出する方法を知っていますか？ http://msdn.microsoft.com/jp-US / Library / GG430026％28V= VS.85％29.ASPX 追加の大型ライブラリを使用しなければならない（libjpegのような）？

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.