Gray balance

[Charles2]

DEN's hint about midtone color cast ("gray balance"?) in the thread on Color Temperature in Color Balance Transform ( http://www.dl-c.com/board/viewtopic.php?f=4&t=268 ) was a mind-blower, to use a term that is so twentieth century.

I am trying "gray balance" as a way to brighten or darken the midtones. Any traps with this procedure:

I open the image in PWP 5 and open Color Balance. If I like the auto balance, I OK it and re-open Color Balance. Then I click to Use this saved .cb settings file:

Code: Select all

ColorBalance 2.0
autowhite 0
autoblack 2
probesize 1
curpt 2
npts 3
pt 0 1 0 0 0 0 0 0
pt 1 1 128 128 128 98 98 98
pt 2 1 255 255 255 255 255 255
end

Some images acquire a bunch of posterization points (visible with the a histogram tool). Not enough testing to know why, but it seems to happen with Olympus E-P1 camera JPGs but not Olympus raw ORF files.

Incidentally, what does the 1 parameter preceding the pairs of color trios represent? Are the formats of .cb and other settings files documented?

Alternatives are to adjust saturation and brightness, on the whole image, in the Midtone tab of the 3-Zone Adjustment transformation, or with Color Correction using a brightness-based mask of the midtones. -- Can anyone comment on the implications of color theory for these alternatives versus "gray balance"?

I often expand dynamic range when there is room on the HSL-L curve. Are there reasons to do gray balance before or after such expansion?

Here is a resized pair where the only difference is that gray balance was used to darken the midtones in one of the images.

With gray balance:
http://farm5.static.flickr.com/4061/453 ... 7e25_o.jpg

Without gray balance
http://farm3.static.flickr.com/2697/453 ... 8475_o.jpg

[den]

Charles2...

I am trying "gray balance" as a way to brighten or darken the midtones. Any traps with this procedure:

I open the image in PWP 5 and open Color Balance. If I like the auto balance, I OK it and re-open Color Balance. Then I click to Use this saved .cb settings file

The reality of your described workflow and *.cb file is to adjust an image’s gray tone distribution from the neutralized black point through the mid-tones to the neutralized white point with the ColorBalance transform in the RGB color space model without any associated minor changes in hues and/or saturations that would either add or remove slight color casts, i.e., R=G=B=Broken-Line curve [0,0], [50,38.4], [100,100] which effectively reduces the R=G=B=[50,50] gray tone to R=G=B=[50,38.4] with straight-line (linear) gradients to the black [0,0]/white [100,100] points… a 11.6% mid-tone reduction from an original 50% gray tone.

While the ColorBalance transform can be used in this manner, perhaps the BrightnessCurve transform in the RGB color space would be easier, …i.e., …apply a RGB BrightnessCurve Broken-Line curve = [0,0], [50,38.4], [100,100] to the “Without gray balance” image to a preference Amount.

…or… perhaps better yet, utilize a darkening contrast ‘S’ curve rather than a single control point Broken-Line curve to adjust mid-tone contrasts to enhance image small detail and prevent possible posterizing, …i.e.,… apply a RGB BrightnessCurve Smooth curve = [0,0], [20,5], [80,80], [100,100] to the “Without gray balance” image to a preference Amount.

Now, click on the resulting gray tone adjusted image and open the ColorBalance transform. Look for things that should be ‘neutral gray’ like the largish, flat bluish stone in the bottom left of the stream… like the bluish tree bark that should be gray in the mid-distance left… or like the bluish, smooth pathway color on the middle right… shift click on these to obtain divergent R,G,B curves that will provide ‘neutral grays’ at these image features… then adjust Amount to a preference.

A possible final image version utilizing the above and starting from the “Without gray balance” image may be observed here:
http://www.dpreview.com/galleries/69222 ... _bc_clrbal

[Charles2]

Thank you for a great tutorial:

--for teaching the Brightness Curve-RGB and something it does that Color Curve transform does not. Working mostly with the latter's HSL-L, I was thrown off by the fact that Color Curve offers separate R, G, and B curves but not a combined one.

--for teaching how to use Color Balance probes for grays and "true" colors, beyond white point and black point. Rereading the manual on the Color Balance transformation, I do not find gray balancing by probes.

We can find explanations of color spaces, which is necessary theory for intelligent post-processing. There are also many good recipes, and each of us can learn by trial and error. However, I have not found much beyond the very basics that provides a recipe while relating it to color and light theory. Your reply is a great example of that. (And PWP lends itself to this endeavor more than any other post-processing program I've seen.)

[den]

However, I have not found much beyond the very basics that provides a recipe while relating it to color and light theory.

...perhaps the void beyond the technology and recipes is meant to be filled with the "artist" that lurks within us by asking "what do I remember the scene looked like?"... or even more daring... "what do I remember that I wish the scene looked like?!!!"

The “Without gray balance” image is a challenging multiple reflective light source image that often occurs in nature... ...there are image areas with: direct sunlight; filtered [dappled] sunlight; skylight reflections in the stream; lightly shaded areas; and darkly shaded areas.

Which source one emphasizes at the expense of the others is perhaps an 'artistic' one.

As the previously suggested tone/color and mid-tone gray balance adjustments occurred in the RGB color space [RGB BrightnessCurve and ColorBalance]...

...is there any interest in suggestions to 'remap' the "Without gray balance” image's data in the HSV color space model for tone/color, gray balance, and overall color temperature ambience where PWP5's Remap transform is used?

[den]

Perhaps the use of a suggested 'Reference Image' to pre-set the Color Range feature of the Mask Tool will simplify the 'artistic' judgements needed to color balance midtones when 'white/grey balance' reference cards are not used during 'capture'. With a pre-set Color Range feature, one can temporarily mask an image's colors with low saturations and mid-tone thereby locating them for analysis with the Readout Tool and/or ColorBalance, ColorCorrect, Remap 'color pickers'....

Unrestricated image use is authorized.

1-99Hue_0-10Sat_45-55Value-2.jpg (10.45 KiB) Viewed 4587 times

For detailed instructions/illustrations, see: http://www.ncplus.net/~birchbay/tutoria ... /index.htm

Charles2...
I hope you do not mind but I documented a Remap tone/color workflow for your "Without gray balance" image version that may be of interest: http://www.ncplus.net/~birchbay/tutoria ... /index.htm . It is very similar to your initial Color Balance settings, except with an added 'Color Temperature' ambience.

[Charles2]

Happy to see what you can do with it, DEN, and of course how you do it.

Masking by color range is difficult for me; it seems extremely sensitive to mouse travel. Perhaps I'll get the knack of it some day.