Sky mottling in B&W

[kiro]

<p>I'm running into this issue on a number of photos out of my 50D where there are mottled bits of the sky when I go to black and white. I can't tell if this is an artifact of the bit depth of my monitor, bit depth in LR preview, or a problem in camera (e.g. lens or sensor issues). I have to order prints from out of state, so before I go through the wait/expense, some feedback would be very helpful. Here's what I got:<br>

The image was captured:</p>

<ul>

<li>Raw</li>

<li>ETTR</li>

<li>1/500 and f/8</li>

</ul>

<p>In Lightroom, I:</p>

<ul>

<li>Adjusted blacks and whites to clipping</li>

<li>Converted to B&W by selecting Bland & White Treatment (Top of "Basic")</li>

<li>Adjusted Blue channel from +5 to -20</li>

<li>Sharpening: Amount 25; Radius 1.0; Detail 25; Masking 39 (used option+mask to adjust masking to the point where sky was masked out)</li>

</ul>

<p>Attached is a 100% crop of a full rez JPG output at max quality - it is representational of what I see in LR. </p>

<p>Any thoughts? I greatly appreciate any feedback<br>

<img src="http://d6d2h4gfvy8t8.cloudfront.net/18283713-lg.jpg" alt="" width="1181" height="830" /></p>

[Robin Smith]

<p>It's probably because you adjusted the blue channel so these are artifacts. You need to lay off the blue channel adjustment a little. You probably will not notice it when you get a print, unless you are printing at 100%.</p>

[kiro]

<p>I guess I didn't think -20 was very drastic, on a scale of -100 to 100. If I want a dark sky without mottling, does this mean I should switch my camera to B&W and put on a red filter? Seems to kinda defeat the purpose a bit...</p>

[alan_cox3]

<p>Hi Kier,<br>

I suppose it's possible that in doing ETTR you over-saturated the blue channel. It's just a possibility. It's not quite as common as blowing out the red channel on flowers, etc. But I've still seen it happen. Were you using an RGB histogram when setting ETTR? Gray histograms will not alert you to the potential problem. Check the blue values in the brightest areas. If there are none close to max value, you are OK.<br>

When doing ETTR, over-saturating a few specular highlight pixels in detail areas will generally be OK. Doing so in larger smooth areas will quickly show up as banding/mottling.<br>

Some folks I know actually have a style setting that increases the contrast when doing ETTR. That way the blinkies are an "early warning" for how close you are getting. (Blinkies are determined by the JPEG setting, ie the style combination.)</p>

 

[kiro]

<p>Alan - that makes a lot of sense. For this series of work I'm doing, which is heavily based on the sky, I'm really pushing the ETTR concept to where I'm getting within a 1/3 stop of clipping. I just switched my info view on my camera to the rgb and see the difference there. I'll shoot like that from now one, and try putting that blue a stop or a little more from clipping and see what I get. Thanks!</p>

[thirteenthumbs]

<p>I shoot B&W film mostly and do not use LR. I live in a large metropolitan area that has light to heavy haze daily, clear skys are a rarity.<br>

Haze, regardless of density, produces different tones in the sky on film in patterns that can resemble mottling even when the tone looks even to one's eye. The same should be true for sensors.</p>

[kiro]

<p>Interesting - do you correct for that in your film process? Or just accept it as life?</p>

[Robin Smith]

<p>Kier</p>

<p>My thought is that you will not notice this in a final print: you are pixel peeping. I also agree somewhat with Charles that blue sky does have microvariations due to atmospheric haze, water vapor etc. We don't notice it as it is changing constantly and subtly, but when pixel peeping this may be the kind of thing you pick up.</p>

[david_henderson]

<p>Not much to see IMO and I agree with Robin that I wouldn't expect to see it on a print. I took it into PS and could see it better at 200%. But noise reduction software (I used Nik Define) got rid of it easily if you don't want to take the chance.</p>

[thirteenthumbs]

<blockquote>

<p>Interesting - do you correct for that in your film process? Or just accept it as life?</p>

</blockquote>

<p>I adjust Levels or Curves as needed to minimize it in PS. If its too drastic I just scrap the photo and no longer go out shooting on very hazy days and try to minimize the sky in the photo on moderately hazy days.</p>

[kiro]

Thanks guys. I wasn't sure if I was pixel

peeping or maybe the jpg review was

introducing artifacts or if it was real. I'll play

with Define to see what happens on the shots

I already have. And I'll try combining that with

backing off the ETTR in the future.

 

Charles I'll take note of hazy days and see

how it impacts the final image.

 

Thanks all!

[sjmurray]

<p>Just a thought, are you processing your raw image at 16 bit? I found I had color problems, I think clipping, in some shots of blue sky and sunset when processing in 8 bit.</p>

[kiro]

<blockquote>

<p ><a href="/photodb/user?user_id=525441">Steve J Murray</a><a href="/member-status-icons"><img title="Subscriber" src="/v3graphics/member-status-icons/sub10plus.gif" alt="" /></a>, Sep 12, 2016; 09:38 p.m.</p>

 

<p>Just a thought, are you processing your raw image at 16 bit? I found I had color problems, I think clipping, in some shots of blue sky and sunset when processing in 8 bit.</p>

 

</blockquote>

 

<p>I've always had Lightroom in 16 bit, but recently finally ran the update to go from 5 to CC, so it's a good thought to double check a setting didn't get reverted. Thanks!</p>

 

[AlanKlein]

<p>What happens if you use a red filter on color digital and then convert to BW in Photoshop and adjust the Blue? Darker skies with the filter than without?</p>