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Having a problem with patchy skin and shadows

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  #11  
Old 08-25-2009, 01:53 AM
sadmunky sadmunky is offline
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Re: Having a problem with patchy skin and shadows

Yes, Quantum , that was exactly the problem I was having in the original and the halfway image.
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  #12  
Old 08-25-2009, 03:01 AM
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Cuervo79 Cuervo79 is offline
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Re: Having a problem with patchy skin and shadows

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Originally Posted by Quantum3 View Post
Cuervo, I think he's reffering to both. AS far as I understand, he wants to even those blotvhy areas but he gets more blocthy stuff when d&bing
I was refering to your post, I do se the blotchy parts the OP wrote about, and I see them in most of the images I retouch. You implied that the blotchy parts are made because they're digital images and that some of them don't even show when printed.

Now my question was how do you judge the ones you say that "don't show on print" and the ones that do?

I thought that the blotchyness was because the effect of light when it hits the topography of the face makes the shadows and all, its something natural with every image.
You wrote that because there's very little range for the shadows (in your example) the blotchyness appears.

That's why I asked
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  #13  
Old 08-25-2009, 04:26 AM
Quantum3 Quantum3 is offline
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Smile Re: Having a problem with patchy skin and shadows

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Originally Posted by Cuervo79 View Post
I was refering to your post, I do se the blotchy parts the OP wrote about, and I see them in most of the images I retouch. You implied that the blotchy parts are made because they're digital images and that some of them don't even show when printed.

Now my question was how do you judge the ones you say that "don't show on print" and the ones that do?

I thought that the blotchyness was because the effect of light when it hits the topography of the face makes the shadows and all, its something natural with every image.
You wrote that because there's very little range for the shadows (in your example) the blotchyness appears.

That's why I asked
Well... Will set appart each thing for better comprehension. I guess I got your question, so I will try to give you an answer.

Bandings is the same than posterization, but it's shown by very noticeable bands of shades (tipycalli in blurry backgrounds, skyes or gray scales/duotone images).

Example here: http://origin.arstechnica.com/news.m..._example01.png

real life example: http://tsedrive.files.wordpress.com/...on-example.jpg

Posterization is when the gradient get lacky, like banding, but the difference is that posterization is present more like a "blotchy" noise.

Example here (exagerated example): http://images.absoluteastronomy.com/...on_example.jpg

real life example: http://bytec.vitanet.lv/tmp/RTB2_posterization.jpg

(both examples looks posterized to me, anyway).

"Blotchy" is slang.

Sometimes, Banding appears depending on the zoom we're looking the image in the screen (same with moire: http://iaaa.nl/cursusAA&AI/gif/div/moireM.jpg) but, as we change the zoom, the moire and banding may dissapear.

When you see the image at full pixels, Banding must be non existent, because the perfect corelation between screen pixels and image pixels but sometimes Banding is still persistent. In that case is because the monitor, not the image. Standard monitors are capable to show no more than a 25% of the total richness of the image. Apple Cinema Display shows 16,7 million of colors exact but sometimes is not enough in order to avoid banding. That's because the amount of shades is surpassing the amount of possible shades that the screen is able to show, overwhelming it.

Same happens with posterization, but if you tryed to blur more and more some puctire, even at 32 bits per channel (let say some HDR without tonemapping) you will keep seeing banding and/or posterization in the image and that's because the screen, which is just 8 bits. Not only lot of out of gamut colors, also shades.

So, posterization and banding is just lack in tonal transitions.

Printers are able to show more tonal transitions than monitors, that's why the image will not show posterization/banding when printed in most of the case, and even less when developing it with chemicals.

The problem with chemicals is the paper hasn't enough dynamic range, meaning they support no more than 3-5 stops and printers cannot represent the richness of RGB colors, but smoother tonal transitions.

Canon had released a new printer about 1 year ago capable to almost print sRGB colors and about few months, Epson released a new ink, called HDR Ink Pentachrome or something like that. Paper still more or less the same but the inks contains micro cristals inside, which reflects the light to boost the colors. I have a friend, who was in Miami, he saw those prints in a private exhibition and he told me it is like the print shines and light all the place. 120usd each ink, and just the little cartridges we're familiarized to buy...

These deffects are common for every single digital thing, that's why film still great for black and white (grayscale). Even scanning film will produce banding/posterization.

There are those monitors Eizo, they're true 16 bits per channel monitors and they have an special thing (still wihout enough info about those) for grayscale images. The gamut those monsters are able to handle are almost ProPhoto RGB or more, cannot remeber too much that part, but much more than Adobe RGB 1998. Eizo: http://www.eizo.com/products/graphics/cg301w/index.asp

In short, we edit pictures in 16 bpc, but screen only shows around the 25-60% of the 8 bpc file... Frustrating...

PS: evening the skin tones with d&b is just acomodating/enagging tones by making those similar among them, making them ecually, tiding them. Just like a puzzle of untidy tones, but the image will have less tonal values in most of the cases beause evening the tones means substracting the diferent ones and making all the image looking even. Sometimes, when exagerating the d&b the images may look flat, because that's d&b, basically. Tone Flattening. Of course, painting with d&b a bit fix that problem, but it should be applied very carefully. Texture fools the eye in most of the cases.

Drag and drop a gradient black to white in PS and you will see how your screen posterizes/banding in the darker tones. Do the same in different quality monitors and rty the same in an Eizo and get amazed

About the tonal values of digital pictures yes, the shadows have the less info/tonal values = lack in tonal transition. Here is a table I have in my HD, let see...

(I love this!)
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File Type: png Valores Tonales entre 10-12-14 bits.png (33.3 KB, 33 views)

Last edited by Quantum3; 08-25-2009 at 04:54 AM.
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  #14  
Old 08-25-2009, 06:33 AM
Quantum3 Quantum3 is offline
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Re: Having a problem with patchy skin and shadows

Cuervo, while retouching I got your question more accurately. The thing you say about light and topography of skin is a total different thing, not directly involved with digital imaging. I was mostly talking about the overal "blotchiness" found from a wide range of levels like 0 to some higher value (like found in a wood ball lit from one direction). The topography of the texture of the ball could be very irregular, but the posterization/banding will be noticeable in the overall transition from light to shadows. More specifically, among the dark tones and even more if the surface is quite polished.
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  #15  
Old 08-25-2009, 11:25 AM
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Cuervo79 Cuervo79 is offline
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Re: Having a problem with patchy skin and shadows

Thanx for your explanation.. I got what you where trying to explain. Well personally the blotchyness I was referring to was the effect light makes on the face.

I haven't had posterisation blotchyness at the moment lol, thanx for explaining I will keep a look out for it..

Cheers
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  #16  
Old 08-26-2009, 12:12 PM
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Markzebra Markzebra is offline
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Re: Having a problem with patchy skin and shadows

With Curves you can correct to any precise destination value. Simple DB curves will not always be enough, you need to go into the channels. Viewing channels (with your discussed preview adjustments) separately can also help. That's the best way but there are also cheaper ways like color overlays, or even masked cruder adjustments like hue/sat and selective color. Many ways to 'skin the cat'. I hate that expression, whoever thought of skinning a cat in the first place.
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  #17  
Old 08-26-2009, 03:52 PM
Gary Gary is offline
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Re: Having a problem with patchy skin and shadows

Quote:
Originally Posted by sadmunky View Post
So I have been working on this file and its getting close to a look I like, but I am having one problem that I do seem to run up against from time to time. Around her mouth are some shadows that run to her cheek and then down to the jaw, they are dark and seem to be muddy/patchy. I tried to D/B them out but that just left them muddy and frosted looking, with the blue tint of the shadow very apparent. So the problem is two fold. 1 to get better texture in there, and 2 to correct the patch of blue tint. Any tips or directions I should be looking in? I would really like to learn how to correct issues like this, for the occasions that they happen. Any tips or places I should look to correct colored patchy skin in general?
Not sure if this is the right direction for you but here's what I did in CS4.
- used empty layers in both lighten and darken mode, sampled the skin color closeby and painted with a very low opacity brush to lighten or darken the shadows, bright skin areas, etc.
- used the healing brush to blend these to the surrounding areas
- curves adjustment layer to reduce the overall blue cast
- painted on a new layer in color mode to enhance the color in the desaturated areas
- Vibrance adjustment to increase saturation
- Grain Surgery match grain on a duplicate and then applied via a hide-all mask
- selective Shadow/Highlights adjustment
- sharpened

Cheers!
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