scale openexr alpha up

scale alpha up to 0 - 255 to match the rest of libvips

ChangeLog

@@ -38,6 +38,8 @@
 - magickload now sniffs some file types itself
 - update radiance load from upstream
 - mapim could fail for float index images with coordinates out of int range
+- scale openexr alpha to 0 - 255
+- close input earlier, when we can [kleisauke]
 
 12/3/18 started 8.6.4
 - better fitting of fonts with overhanging edges [Adrià]

libvips/foreign/openexr2vips.c

@@ -16,6 +16,8 @@
  * 	- tag output as scRGB
  * 16/8/18
  * 	- shut down the input file as soon as we can [kleisauke]
+ * 19/8/18
+ * 	- scale alpha up to 0 - 255 to match the rest of libvips
  */
 
 /*
@@ -332,8 +334,16 @@ vips__openexr_generate( VipsRegion *out,
 				float *q = (float *) VIPS_REGION_ADDR( out,
 					hit.left, hit.top + z );
 
+				int i;
+
 				ImfHalfToFloatArray( 4 * hit.width, 
 					(ImfHalf *) p, q );
+
+				/* oexr uses 0 - 1 for alpha, but vips is 
+				 * always 0 - 255, even for scrgb images.
+				 */
+				for( i = 0; i < hit.width; i++ ) 
+					q[4 * i + 3] *= 255;
 			}
 		}
 
@@ -402,6 +412,8 @@ vips__openexr_read( const char *filename, VipsImage *out )
 		read_header( read, out );
 
 		for( y = 0; y < height; y++ ) {
+			int i;
+
 			if( !ImfInputSetFrameBuffer( read->lines,
 				imf_buffer - left - (top + y) * width,
 				1, width ) ) {
@@ -417,6 +429,12 @@ vips__openexr_read( const char *filename, VipsImage *out )
 			ImfHalfToFloatArray( 4 * width, 
 				(ImfHalf *) imf_buffer, vips_buffer );
 
+			/* oexr uses 0 - 1 for alpha, but vips is always 0 -
+			 * 255, even for scrgb images.
+			 */
+			for( i = 0; i < width; i++ ) 
+				vips_buffer[4 * i + 3] *= 255;
+
 			if( vips_image_write_line( out, y, 
 				(VipsPel *) vips_buffer ) )
 				return( -1 );