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Author Topic: Exposing for B&W digital?  (Read 6171 times)

GrahamBy

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Re: Exposing for B&W digital?
« Reply #20 on: September 09, 2016, 09:11:14 AM »

To me it makes no sense: the reduction to BW is just a weighted sum of different colours. Hue and saturation are about individually transforming those colour components to something else: it relates to the colour output, which is not seen. Only colour luminance relates to the colour input, so it makes sense that only that is relevant to the B&W result.

Including the extra controls just provides you with 18 controls which provide the same range of output variation as the 6 in LR, so far as I can see.
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BartvanderWolf

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Re: Exposing for B&W digital?
« Reply #21 on: September 09, 2016, 09:39:58 AM »

To me it makes no sense: the reduction to BW is just a weighted sum of different colours. Hue and saturation are about individually transforming those colour components to something else: it relates to the colour output, which is not seen.

Hi Graham,

That not necessarily true. Suppose you have a shade of green and a shade of (dark)yellow-green, say some foliage and grasses that you want to get some more separation in. With a Green or Yellow filter one would lighten the tonality of both approximately the same. But when the Green is Hue shifted towards Cyan, and the YellowGreen is Hue shifted towards Orange, it becomes possible to enhance the contrast between those shades by applying a color filter (e.g. a Redfilter would lighten the now Orange, and darken the now Cyan green). Alternatively one could lessen the contrast by Hue shifting both colors closer to the same hue, and filtering with Green for lightening or Blue or Red to darkening. This is of course much easier to do with a dedicated tool than only the generic LR controls and adjustments.

Quote
Only colour luminance relates to the colour input, so it makes sense that only that is relevant to the B&W result.

So it's not 'only', but instead yet another way of controlling tonality in the resulting B&W rendering.

Quote
Including the extra controls just provides you with 18 controls which provide the same range of output variation as the 6 in LR, so far as I can see.

More controls offer more ways to add or modify to the strength of tone adjustment.

Cheers,
Bart
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N80

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Re: Exposing for B&W digital?
« Reply #22 on: September 09, 2016, 10:55:56 AM »

Correct. And in my limited understanding the 'blue' slider in the B&W conversion tool, for instance, affects a specific blue or range(?) of blue. Changing the saturation and hue changes how the 'blue' B&W slider affects the blues in the image.  But yes, the luminance slider has the greatest impact.

For folks who are really deep into B&W tone control I recommend trying this approach. I have found it particularly useful in achieving a red filter effect to darken blue skies. Just applying the red filter in Silver Efex or the blue slider in LR will often result in banding and noise before the desired effect is reached. Using the HSL sliders gives a slight, but still significant level of control in darkening that blue without adding artifacts.
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GrahamBy

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Re: Exposing for B&W digital?
« Reply #23 on: September 09, 2016, 03:42:34 PM »

With a Green or Yellow filter one would lighten the tonality of both approximately the same. But when the Green is Hue shifted towards Cyan, and the YellowGreen is Hue shifted towards Orange,

Thanks Bart,

That means there are two filter steps? Having a separate hue slider on each of the separate colours suggests that there is first a filter applied to define on which wedge of the a*b* plane the hue-shift will apply. So if it were impossible to separate them to adjust luminance, it would be equally impossible to separate them to apply different hue shifts.

Obviously that is an over simplification, since the real issue is that the transition zone of the filter in the angular component is not sufficiently steep, and one would really like a higher-order filter. However ganging together two low-order filters is a pretty ineffective way of doing that, from memory. And then the idea of having ringing artifacts from higher order theta-space filtering is a little disturbing, but maybe I'm too squeamish.

So am I missing something here?

Regards,
Graham
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Guillermo Luijk

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Re: Exposing for B&W digital?
« Reply #24 on: September 10, 2016, 05:31:24 AM »

I always wondered (but didn't have time to implement) how a locally adaptive B&W algorithm would work, calculating the weight of each RGB RAW channel to build a customized B&W output for every pixel area in order to maximize either:
- SNR (highest RAW channels weight more)
- Micro contrast (highest HPF output channels weight more)
- A mix of both SNR and micro contrast

The obtained luminance can look quite weird in terms of real world perceived luminance but could be rearranged starting from a robust B&W conversion in terms of initial noise and/or microcontrast.

I'll have some 2-3 weeks free in the next times so perhaps I try these strategies.

Regards

www.guillermoluijk.com
« Last Edit: September 10, 2016, 05:35:59 AM by Guillermo Luijk »
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BartvanderWolf

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Re: Exposing for B&W digital?
« Reply #25 on: September 10, 2016, 12:46:22 PM »

Thanks Bart,

That means there are two filter steps? Having a separate hue slider on each of the separate colours suggests that there is first a filter applied to define on which wedge of the a*b* plane the hue-shift will apply. So if it were impossible to separate them to adjust luminance, it would be equally impossible to separate them to apply different hue shifts.

Obviously that is an over simplification, since the real issue is that the transition zone of the filter in the angular component is not sufficiently steep, and one would really like a higher-order filter. However ganging together two low-order filters is a pretty ineffective way of doing that, from memory. And then the idea of having ringing artifacts from higher order theta-space filtering is a little disturbing, but maybe I'm too squeamish.

So am I missing something here?

Hi Graham,

The default user interface of most applications is not ideal for such things, and would probably require lots of local selections and adjustments. A dedicated B&W conversion plugin will make life a lot easier. Also, real-time updated previews will make setting the parameter levels a more creative process.

Cheers,
Bart
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