Digital BW, The Print

Hi!
I intend to calibrate my HP G4050 in order to make ICCs for some 
watercolor papers I have. I am following Paul Roark�s directions 
(http://paulroark.com/BW-Info/Making_B-W_ICCs.htm). In this article, 
Paul advises to use highlight, shadow and gamma controls for 
calibration. Vuescan, however, does employ this terminology. My 
question, for those familiar with Vuescan, is: am I right in assuming 
that, in the Color tab, black point and white point controls correspond 
to shadow and highligth, and that brightness correspond to gamma?

Edson

It looks like you are quite right.

http://www.hamrick.com/vuescan/html/vuesc26.htm#topic25 
has the following quotes regarding 
Brightness, White Point and Black Point:

     "Brightness

     Use this option to increase or decrease 
the overall image brightness.
     VueScan's brightness is effectively a 
multiplier of the gamma of the color space."

  "White point (%)

     The white point is used by the color 
balance algorithm and is computed by using 
the histogram of each color in the image. Use 
this option to leave the white point at the 
maximum intensity (0%), or to choose the 
white point such that some percentage of the 
pixels in the image are above the white point.

     The default white point is 1% (that is, 
the brightest 1% of pixels are all converted 
to pure white). Setting a higher value will 
cause tones close to white to become pure 
white. This can improve contrast and overall 
intensity of the image. Setting the white 
point too high will cause details in areas of 
highlights (e.g. the gray puffs of a cloud) 
to be lost, making the image look flat."

"Black point (%)

     The black point is used by the color 
balance algorithm and is computed by using 
the histogram of each color in the image. Use 
this option to leave the black point at the 
minimum intensity (0%), or to choose the 
black point such that some percentage of the 
pixels in the image are below the black point.

     The default black point is 0. Setting a 
higher value will cause tones close to black 
to become pure black, which can improve 
contrast. However, setting the black point 
too high will cause shadow detail to be lost."

I believe that the best way to calibrate a scanner with Vuescan is to use an
IT8 target and the "profile" tab.
Jorge