saturation, hue and clipped channels

[sgwrx]

i took a shot of a pink/red wild rose tonight.  the basic exposure fit nicely in the histogram ie. no clipped colors or luminosity. i converted from RAW into ProPhoto 16bit.

i added a hue/saturation layer with blend mode of color. i marqueed the rose and watched the 3-channel histogram as i adjusted the master saturation level. i brought it up to +18 and found that the blue channel clipped on the highlight end quite a bit.

instead of backing off the saturation, i thought of adjusting the master hue to see what would happen to the individual channels. sure enough as i moved the hue to the right, the clipped blue channel moved to the left, thus "unclipping".

this is where my question is. when the blue was clipped with the saturation only adjustment, it of course spiked quite a bit and bunched up to the right. as i adjusted the hue, the spike did not go away, nor did the bunching. instead it all just moved back toward the left, away from clipping. there appears to be a tiny little bit of a bump between the spike (and bunch) and the right side of the histogram. so, am i still loosing information in the blue channel via clipping? loosing tonality in the blue?

thanks!
steve

[alainbriot]

Steve,

If I understand what you did correctly, by changing the hue you actually moved to a hue that had a different saturation level (lower in your instance), hence effectively dropping the saturation clipping.  Not all hues saturate to the same extent.  This is true both for different hues and for different tones in a single hue.  Furthermore, the maximum saturation in a single hue doesn't always happen for the brightest tone in this hue. For example, with reds, the maximum saturation is actually around a tone of 3 or 4 on a 0 to 8 tone scale, 0 being black and 8 white.

If my analysis is correct (hard to say without seeing the actual colors), the changes in your image will be a change of hue and a drop in saturation in that hue.

[sgwrx]

HA! it took a couple of days to think about it, but yes you are understanding my explanation correctly. and yep i get it now.

i totally get the idea of 'hue' now.  in Capture One LE, they have that hue-circle with white in the middle and the most saturated colors on the perimeter.

so yes, what i was doing was completely changing the hue of that particular redish color in the rose.  really it's a totally different color now, the rose, because of this. or more correctly contains different colors.

i remember back to one of the books - a fully saturated color such as blue or red can still be "dark" whereas a fully saturated yellow is bright in comparison.

i'm going to search, but is there some type of graphical "map" that relates colors to luminosity, which i think is what you were eluding to.

[sgwrx]

there's much on this via google.  here's an interesting site i came across: http://www.marginalsoftware.com/HowtoScan/..._as_a_tool2.htm

this is just one page of many (there are forward and backward buttons at the bottom).


EDIT (Added): Actually i can just use the luminsoity histogram on an image filled with solid colors to figure out what "level" or gray tone the color is.