Implement a custom DCT filter callback for lossless transforms

git-svn-id: svn://svn.code.sf.net/p/libjpeg-turbo/code/trunk@703 632fc199-4ca6-4c93-a231-07263d6284db

1 files changed, 35 insertions, 0 deletions

diff --git a/turbojpeg.h b/turbojpeg.h
index e4c5779..f0c542c 100644
--- a/turbojpeg.h
+++ b/turbojpeg.h
@@ -315,6 +315,13 @@ enum TJXOP
  * a grayscale output image.
  */
 #define TJXOPT_GRAY     8
+/**
+ * This option will prevent #tjTransform() from outputting a JPEG image for
+ * this particular transform (this can be used in conjunction with a custom
+ * filter to capture the transformed DCT coefficients without transcoding
+ * them.)
+ */
+#define TJXOPT_NOOUTPUT 16
 
 
 /**
@@ -376,6 +383,34 @@ typedef struct
    * The bitwise OR of one of more of the @ref TJXOPT_CROP "transform options"
    */
   int options;
+  /**
+   * A callback function that can be used to modify the DCT coefficients
+   * after they are losslessly transformed but before they are transcoded to a
+   * new JPEG file.  This allows for custom filters or other transformations to
+   * be applied in the frequency domain.
+   *
+   * @param coeffs pointer to an array of DCT coefficients.  (NOTE: this
+   *        pointer is not guaranteed to be valid once the callback returns, so
+   *        applications wishing to hand off the DCT coefficients to another
+   *        function or library should make a copy of them within the body of
+   *        the callback.)
+   * @param arrayRegion region structure containing the width and height of the
+   *        DCT coefficient array as well as its offset relative to the
+   *        component plane.  TurboJPEG implementations may choose to split
+   *        each component plane into multiple DCT coefficient arrays and call
+   *        the callback function once for each array.
+   * @param planeRegion region structure containing the width and height of the
+   *        component plane to which this DCT coefficient array belongs
+   * @param componentIndex the component plane to which this DCT coefficient
+   *        array belongs (Y, Cb, and Cr are, respectively, 0, 1, and 2 in
+   *        typical JPEG images.)
+   * @param transformIndex the transformed image to which this DCT coefficient
+   *        array belongs
+   *
+   * @return 0 if the callback was successful, or -1 if an error occurred.
+   */
+  int (*customFilter)(short *coeffs, tjregion arrayRegion,
+    tjregion planeRegion, int componentIndex, int transformIndex);
 } tjtransform;
 
 /**