High key contrast method (post-processing tip)

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Beatsy
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High key contrast method (post-processing tip)

Post by Beatsy »

Just posting to show a method I sometimes use to get a (kind of) high-key contrasty look with heavily cropped images. The images naturally dropped out of the process and I thought the technique might be novel to a few. This is just *a* method, not best, or even any good at all in many applications, but it worked quite well for this particular subject (a dandelion). The end result will likely not be to everyone's tastes though...

Anyway, to the pics. I nearly always use a zoomed-in view in the electronic viewfinder when shooting hi-mag macro hand-held. When I later review what I captured, I often come across shots like this and wonder what the bleep I was trying to shoot.
dandelion sooc.jpg
Thing is, the picture *I* shot was the zoomed-in view not the whole full-frame image. So I crop the image to what I'd framed and intended to capture.
dandelion-crop.jpg
Still plenty of pixels to work with, but being a dandelion and entirely yellow, it's really hard to boost details contrast with the usual sliders. Especially for the high-key look I wanted. If you push too far in this (all yellow) image, detail just goes similar shades of bright (or dark) yellow and disappears. This is as about far as I'd push sharpening and contrast the "usual" ways.
dandelion-sharp.jpg
Not contrasty enough by far. I want that high key (ish) look with more punch in the highlights and murk in the darkest shadows. So I made a copy of the image and converted it to black and white. It is *much* easier to use B&W colour conversion sliders to get the tonal ranges needed. Some wiggling of those along with levels and curves adjustments gave this "high key" result...
Dandelion-bw.jpg
A bit harsh, but that's on purpose. Now the original sharpened colour image is loaded into Affinity Photo (or Photoshop), then the B&W conversion is loaded into another layer on top. The images are perfectly aligned because they are the same image processed differently. Then the "blend mode" of the B&W image is changed to "luminance". Adjust opacity to get the strength of effect you want and "ta-daa" - a contrasty, high-key result that preserves lovely smooth tonal transitions between widely-separated light and dark areas. Some may hate it, but I prefer it to the rather flat look that bright, "mono coloured" flowers usually exhibit.
dandelion-bwluminance.jpg
Note: I can't get this effect when working with just the colour image - which is why I do this. But I may simply be incompetent. If the 2nd image can be given the same look as the last using sliders alone (and no fiddly masking) then I'm all ears. Cheers.

I mage was shot on A7rii with adapted Canon MP-E65 at 3x or so - single shot at f/9. Macro flash used

Chris S.
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Re: High key contrast method (post-processing tip)

Post by Chris S. »

Steve,

Similar but simpler?

In Photoshop:

1. Convert image from RGB color to Lab color (Menu: Image>Mode>Lab color)
2. Isolate lightness channel (Channels palette: Turn off Lab, a, and b, leaving on "Lightness")
3. Adjust lightness channel (For example--Menu: Image>Shadows/Highlights>Shadows 35%, Highlights 0%>OK)
4. Convert image back to RGB color (Menu: Image>Mode>RGB color)

--Chris S.

Beatsy
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Re: High key contrast method (post-processing tip)

Post by Beatsy »

Thanks Chris, that was my first thought (and attempt). The "L" in lab is "Luminance" and it does indeed give you a greyscale image representing luminance which can be manipulated as you suggest. But it doesn't quite do enough to get the wider tonal changes needed for those near-white background highlights (with the smooth tonal transition to the yellows).

The key difference is that B&W conversion allows you to adjust the contribution of individual hues to brightness in (what becomes) the luminance channel. You can't do that with LAB mode conversion, you just get a flat, constant conversion of all luminance values relative to their hue. That means you can't target certain hues (which often correlates with certain features) to be lighter or darker for more local contrast. It results in the same, flat, "all yellow" hues/tones that you get from trying to adjust the RGB image directly. Or the tone transitions become much "faster" and choppier looking (almost pixellated at the small-details level). A good (as in desired) result seems to depend mostly on judicious slider wiggling during B&W conversion.

I may have done something wrong on previous tests, I'll revisit it on the next go, but as I already tried and failed a few times I'm pretty sure the limitation is real.
Last edited by Beatsy on Tue Apr 13, 2021 1:29 am, edited 1 time in total.

Chris S.
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Re: High key contrast method (post-processing tip)

Post by Chris S. »

Steve,

I had also thought of the "L" in lab as standing for "Luminance," but my version of Photoshop calls it "Lightness." Wikipedia indicates that in Lab color, lightness is a derivative of luminance: "The lightness value, L* in CIELAB is calculated using the cube root of the relative luminance with an offset near black. . . ."
Beatsy wrote:
Mon Apr 12, 2021 11:23 pm
But it doesn't quite do enough to get the wider tonal changes needed for those near-white background highlights (with the smooth tonal transition to the yellows).
Step 3 in my example above was a rough placeholder. Would a curves adjustment serve your purpose--adjusting both the lightness and the b channels?

--Chris S.

Beatsy
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Re: High key contrast method (post-processing tip)

Post by Beatsy »

Chris S. wrote:
Tue Apr 13, 2021 1:15 am
...
Beatsy wrote:
Mon Apr 12, 2021 11:23 pm
But it doesn't quite do enough to get the wider tonal changes needed for those near-white background highlights (with the smooth tonal transition to the yellows).
Step 3 in my example above was a rough placeholder. Would a curves adjustment serve your purpose--adjusting both the lightness and the b channels?
I did try all the possible curve and even LUT adjustments on the lightness channel, but couldn't get control over the specific hues I wanted to with the AB channels. That might be me - but I find the way I do it now more intuitive with simple slider control over 8 basic hues, plus specific control over precise hue ranges picked from the image. The process is about the same amount of work. With the image loaded in Affinity..

1. Duplicate the layer (Ctrl+J)
2. Add (attach) a B&W adjustment layer and shift relative brightness/contrast of required hues using sliders - until the B&W tones look "right"
3. Convert layer blend mode to Luminance
4. Adjust layer opacity for strength of effect (or mask it and brush the effect in selectively - I didn't do that here).

You can go back and adjust the B&W conversion layer after the fact and see the live result in the full colour image.

But I will still have another look at LAB mode way when I next do this. Cheers
Last edited by Beatsy on Tue Apr 13, 2021 12:59 pm, edited 1 time in total.

rjlittlefield
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Re: High key contrast method (post-processing tip)

Post by rjlittlefield »

For whatever it's worth...

After Beatsy's first post I immediately tried Lab in Photoshop, using a Curves adjustment layer on the "Lightness" channel. What I found was that even with Lightness pushed to its upper limit, the resulting image went nowhere beyond a bright yellow, something like RGB=[255,255,48]. In contrast, Beatsy's final image contains some pixels that are pure white RGB=[255,255,255], and many others that are close to that, for example RGB=[254,254,242].

I'm pretty naive about adjustments in Lab mode, but for the moment my results are the same as Beatsy's. I can't get the intended effect either, just by using curves/levels adjustments.

--Rik

Edit: to correct a typo. [254,254,2] is not close to pure white!

Lou Jost
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Re: High key contrast method (post-processing tip)

Post by Lou Jost »

The key difference is that B&W conversion allows you to adjust the contribution of individual hues to brightness in (what becomes) the luminance channel.
I think that is right, it's the main reason why here are special B+W conversion operators in addition to a simple Convert to Grayscale command

Beatsy
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Re: High key contrast method (post-processing tip)

Post by Beatsy »

Haha. I shall bask in the warm glow of vindication courtesy of Lou and Rik. Well, "for the moment", at least :D

Thanks both.

In my haste I forgot to sharpen the final one for output. Here it is, in conclusion, with final adjustments. This is more like the view I "saw" (perceived? interpreted? imagined?) in the viewfinder. Exaggerated so the viewer is prompted to see it too.
dandelion-bwluminance-focus.jpg

soldevilla
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Re: High key contrast method (post-processing tip)

Post by soldevilla »

Photoshop place layers in "normal" mode by default and that affects color. I convert the layers of levels and curves to "luminosity" mode and that allows me great modifications without affecting the color

MarkSturtevant
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Re: High key contrast method (post-processing tip)

Post by MarkSturtevant »

It seems a good method to bring into the workflow, at least on occasion.
One thing to maybe try is to add a UV light into the set-up. Perhaps as some pictures with the UV included, and others without. Plants will fluoresce a bit, and with the addition of layer masks you might blend that in to add enhancements.
Mark Sturtevant
Dept. of Still Waters

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