rename vips_gammacorrect() as vips_gamma()

and swap exp to 1 / exp

also works for any format

ChangeLog

@@ -16,6 +16,8 @@
 - radiance load supports sequential read
 - rewritten radiance decode is much faster
 - add vips_crop(), a synonym for vips_extract_area()
+- rename vips_gammacorrect() as vips_gamma(), now takes 1 / exp
+- vips_gamma() works for any format
 
 18/10/13	started 7.36.3
 - fix compiler warnings in ubuntu 13.10

libvips/conversion/gammacorrect.c

@@ -1,4 +1,4 @@
-/* Gamma-correct image with factor gammafactor.
+/* Raise an image to a gamma factor
  *
  * Copyright: 1990, N. Dessipris.
  * 
@@ -11,6 +11,10 @@
  * 	- 16 bit as well
  * 1/8/13
  * 	- redone as a class
+ * 11/11/13
+ * 	- any format
+ * 	- calculate pow(1/exp) rather than pow(exp) to be consistent with
+ * 	  other packages
  */
 
 /*
@@ -49,50 +53,76 @@
 
 #include "pconversion.h"
 
-typedef struct _VipsGammacorrect {
+typedef struct _VipsGamma {
 	VipsConversion parent_instance;
 
 	VipsImage *in;
 	double exponent;
-} VipsGammacorrect;
+} VipsGamma;
 
-typedef VipsConversionClass VipsGammacorrectClass;
+typedef VipsConversionClass VipsGammaClass;
 
-G_DEFINE_TYPE( VipsGammacorrect, vips_gammacorrect, VIPS_TYPE_CONVERSION );
+G_DEFINE_TYPE( VipsGamma, vips_gamma, VIPS_TYPE_CONVERSION );
+
+/* For each input format, what we normalise the pow() about.
+ */
+static double vips_gamma_maxval[10] = {
+/* UC  */	UCHAR_MAX,
+/* C   */	SCHAR_MAX,
+/* US  */	USHRT_MAX,
+/* S   */	SHRT_MAX,
+/* UI  */	UINT_MAX,
+/* I  */	INT_MAX,
+/* F  */	1.0,
+/* X  */	1.0,
+/* D  */	1.0,
+/* DX */	1.0
+};
 
 static int
-vips_gammacorrect_build( VipsObject *object )
+vips_gamma_build( VipsObject *object )
 {
-	VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( object );
 	VipsConversion *conversion = VIPS_CONVERSION( object );
-	VipsGammacorrect *gammacorrect = (VipsGammacorrect *) object;
+	VipsGamma *gamma = (VipsGamma *) object;
 	VipsImage **t = (VipsImage **) vips_object_local_array( object, 5 );
-	VipsImage *in = gammacorrect->in;
+	VipsImage *in = gamma->in;
+	double scale;
 
-	double mx1, mx2;
-
-	if( VIPS_OBJECT_CLASS( vips_gammacorrect_parent_class )->
+	if( VIPS_OBJECT_CLASS( vips_gamma_parent_class )->
 		build( object ) )
 		return( -1 );
 
-	if( vips_check_u8or16( class->nickname, in ) ||
-		vips_identity( &t[0], 
-			"ushort", in->BandFmt == VIPS_FORMAT_USHORT,
-			NULL ) ||
-		vips_pow_const1( t[0], &t[1], gammacorrect->exponent, NULL ) ||
-		vips_max( t[0], &mx1, NULL ) ||
-		vips_max( t[1], &mx2, NULL ) ||
-		vips_linear1( t[1], &t[2], mx1 / mx2, 0, NULL ) ||
-		vips_cast( t[2], &t[3], in->BandFmt, NULL ) ||
-		vips_maplut( in, &t[4], t[3], NULL ) ||
-		vips_image_write( t[4], conversion->out ) ) 
-		return( -1 );
+	scale = pow( vips_gamma_maxval[in->BandFmt], 
+			gamma->exponent ) / 
+			vips_gamma_maxval[in->BandFmt];
+
+	if( in->BandFmt == VIPS_FORMAT_UCHAR &&
+		in->BandFmt == VIPS_FORMAT_USHORT ) {
+		if( vips_identity( &t[0], 
+				"ushort", in->BandFmt == VIPS_FORMAT_USHORT,
+				NULL ) ||
+			vips_pow_const1( t[0], &t[1], 
+				1.0 / gamma->exponent, NULL ) ||
+			vips_linear1( t[1], &t[2], 1.0 / scale, 0, NULL ) ||
+			vips_cast( t[2], &t[3], in->BandFmt, NULL ) ||
+			vips_maplut( in, &t[4], t[3], NULL ) ||
+			vips_image_write( t[4], conversion->out ) ) 
+			return( -1 );
+	} 
+	else {
+		if( vips_pow_const1( in, &t[1], 
+				1.0 / gamma->exponent, NULL ) ||
+			vips_linear1( t[1], &t[2], 1.0 / scale, 0, NULL ) ||
+			vips_cast( t[2], &t[3], in->BandFmt, NULL ) ||
+			vips_image_write( t[3], conversion->out ) ) 
+			return( -1 );
+	} 
 
 	return( 0 );
 }
 
 static void
-vips_gammacorrect_class_init( VipsGammacorrectClass *class )
+vips_gamma_class_init( VipsGammaClass *class )
 {
 	GObjectClass *gobject_class = G_OBJECT_CLASS( class );
 	VipsObjectClass *vobject_class = VIPS_OBJECT_CLASS( class );
@@ -101,9 +131,9 @@ vips_gammacorrect_class_init( VipsGammacorrectClass *class )
 	gobject_class->set_property = vips_object_set_property;
 	gobject_class->get_property = vips_object_get_property;
 
-	vobject_class->nickname = "gammacorrect";
-	vobject_class->description = _( "gammacorrect a pair of images" );
-	vobject_class->build = vips_gammacorrect_build;
+	vobject_class->nickname = "gamma";
+	vobject_class->description = _( "gamma an image" );
+	vobject_class->build = vips_gamma_build;
 
 	operation_class->flags = VIPS_OPERATION_SEQUENTIAL_UNBUFFERED;
 
@@ -111,48 +141,48 @@ vips_gammacorrect_class_init( VipsGammacorrectClass *class )
 		_( "in" ), 
 		_( "Input image" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
-		G_STRUCT_OFFSET( VipsGammacorrect, in ) );
+		G_STRUCT_OFFSET( VipsGamma, in ) );
 
 	VIPS_ARG_DOUBLE( class, "exponent", 0, 
 		_( "exponent" ), 
 		_( "Gamma factor" ),
 		VIPS_ARGUMENT_OPTIONAL_INPUT,
-		G_STRUCT_OFFSET( VipsGammacorrect, exponent ),
+		G_STRUCT_OFFSET( VipsGamma, exponent ),
 		0.000001, 1000.0, 2.4 );
 
 }
 
 static void
-vips_gammacorrect_init( VipsGammacorrect *gammacorrect )
+vips_gamma_init( VipsGamma *gamma )
 {
-	gammacorrect->exponent = 2.4;
+	gamma->exponent = 1.0 / 2.4;
 }
 
 /**
- * vips_gammacorrect:
+ * vips_gamma:
  * @in: input image 
  * @out: output image
  * @...: %NULL-terminated list of optional named arguments
  *
  * Optional arguments:
  *
- * @exponent: gamma factor, default 2.4
+ * @exponent: gamma, default 1.0 / 2.4
  *
- * Gamma-correct an 8- or 16-bit unsigned image with a lookup table. The
- * output format is the same as the input format.
+ * Calculate @in ** (1 / @exponent), normalising to the maximum range of the
+ * input type. For float types use 1.0 as the maximum. 
  *
  * See also: vips_identity(), vips_pow_const1(), vips_maplut()
  *
  * Returns: 0 on success, -1 on error
  */
 int
-vips_gammacorrect( VipsImage *in, VipsImage **out, ... )
+vips_gamma( VipsImage *in, VipsImage **out, ... )
 {
 	va_list ap;
 	int result;
 
 	va_start( ap, out );
-	result = vips_call_split( "gammacorrect", ap, in, out );
+	result = vips_call_split( "gamma", ap, in, out );
 	va_end( ap );
 
 	return( result );

libvips/deprecated/vips7compat.c

@@ -4150,8 +4150,8 @@ im_gammacorrect( IMAGE *in, IMAGE *out, double exponent )
 {
 	VipsImage *x;
 
-	if( vips_gammacorrect( in, &x, 
-		"exponent", exponent,
+	if( vips_gamma( in, &x, 
+		"exponent", 1.0 / exponent,
 		NULL ) )
 		return( -1 );
 

libvips/include/vips/conversion.h

@@ -186,7 +186,7 @@ int vips_flatten( VipsImage *in, VipsImage **out, ... )
 
 int vips_falsecolour( VipsImage *in, VipsImage **out, ... )
 	__attribute__((sentinel));
-int vips_gammacorrect( VipsImage *in, VipsImage **out, ... )
+int vips_gamma( VipsImage *in, VipsImage **out, ... )
 	__attribute__((sentinel));
 
 int im_insertset( VipsImage *main, VipsImage *sub, VipsImage *out, int n, int *x, int *y );