Go back to specifying Rec 709 because it's slightly different and Rec 709 is mentioned elsewhere in the documentation

git-svn-id: http://svn.code.sf.net/p/netpbm/code/userguide@3169 9d0c8265-081b-0410-96cb-a4ca84ce46f8

1 files changed, 11 insertions, 10 deletions

diff --git a/ppm.html b/ppm.html
index a0086642..ca695e14 100644
--- a/ppm.html
+++ b/ppm.html
@@ -82,16 +82,17 @@ significant byte is first.
 <P>A row of an image is horizontal.  A column is vertical.  The pixels
 in the image are square and contiguous.
      
-<p>In the raster, the sample values are "nonlinear." They are proportional to
-the intensity of the ITU-R Recommendation BT.601 625-line red, green, and blue
-in the pixel, adjusted by the BT.601 gamma transfer function.  (That transfer
-function specifies a gamma number of 2.2 and has a linear section for small
-intensities).  A value of Maxval for all three samples represents CIE D65
-white (as specified by BT.601) and the most intense color in the color
-universe of which the image is part (the color universe is all the colors in
-all images to which this image might be compared).
-
-<p>BT.601 is identical to ITU-R Recommendation BT.709 in these respects.
+<p>In the raster, the sample values are "nonlinear." They are
+proportional to the intensity of the ITU-R Recommendation BT.709 red,
+green, and blue in the pixel, adjusted by the BT.709 gamma transfer
+function.  (That transfer function specifies a gamma number of 2.2 and
+has a linear section for small intensities).  A value of Maxval for
+all three samples represents CIE D65 white and the most intense color
+in the color universe of which the image is part (the color universe
+is all the colors in all images to which this image might be
+compared).
+
+<p>BT.709's range of channel values (16-240) is irrelevant to PPM.
 
 <p>ITU-R Recommendation BT.709 is a renaming of the former CCIR
 Recommendation 709.  When CCIR was absorbed into its parent