What is this halo?

[alioffe]

<p>I'm wondering what is this halo (halo_color.jpg): a strip around the sun where the red looks more pronounced. I have feeling that this is not an optical effect, but something to do with RAW conversion and camera profiles. Depend on my lightroom settings: contrast, exposure, profiles - the diameter is bigger or smaller more or less pronounced. It is not seen after conversion to black and whie (see halo_BW.jpg) where the gradient is nice and smooth.<br>

How to eliminate it? By eliminating I mean not retouching, but rather applying a "right" conversion method</p><div></div>

[alioffe]

<p>No halo in B&W</p><div></div>

[craigd]

<p>If you have some sort of "highlight compression" or "highlight recovery" option in your raw converter, it could produce an effect like that. Try adjusting its settings (or turning it off) to see if the halo changes or goes away. The tone and luminance curves could also affect this.</p>

[alioffe]

<p>Thank you Craig for the quick response. I'm using the LR 3.3, CR 6.3. If you talking about Fill and Recovery options, yes I have Fill setting. Now the next image with Fill = 0. It makes it even worse.</p><div></div>

[danield]

<p>I'm not expert on this but I think it's a result of clipping of the red chanel before the others. The halo appears around the area where the red channel begins to be clipped towards the centre of the image - in that area the intensity of red is beyond the capture capabilities of the camera. Because it is 'clipped', i.e. it is set to the maximum value the camera can record, it creates a distortion as it remains at a flat value instead of increasing together with the other channels. This creates a perceptive color distorsion. Digital cameras are particularly bad at dealing with very strong reds, and color accuracy towards the top of the channels suffers.<br>

I'm not sure what a good solution for this would be - underexposing the shot and then increasing the exposure in software? Maybe other people have better suggestions</p>

<p> </p>

[peterbcarter]

<p>Hold down the alt keys while adjusting your exposure and blacks. This will visually show you when you get clipping. After these two are set, adjust the rest of the sliders and see if your halo disappears.</p>

[alioffe]

<p>Peter,<br />I understand what you are saying, but I'm afraid that this is more serious than just clipping which could be correted in LR. I can adjust exposure to the level when only sun disk is 100% in all channels and cliiped. Than in yellow area the red is 97% (in other channels is less) and then it is less while moving away from the center. It does not help. See attached picture. Also as I told I played with adjusments and profiles it does not help much<br />Daniel,<br />What about the picture converted to B&W. It looks like id does not have the halo. The distortion means the loss some information in red channel. So the converted picture is expected to have this loss as well. Unless the B&W converter knows exactly what the loss is and compensates it accordingly. I do not think it is possible.<br />Is there a way to read and display RAW file without profile conversion?</p><div></div>

[peterbcarter]

<p>Alex, from what you are saying, the luminance is not saturating but the colour is. You may fix this by going to the colour slides and reducing the colour where the halo actually is. Sorry I can't get more specific, but I am at work without LR in front of me.... ;)</p>

 

[alioffe]

<p>Peter,<br>

I tried to play with local hue, saturation and luminocity adjusments. The problem is that in LR the whole picture is affected (you can see the picture here: <a href="../photo/12270170">http://www.photo.net/photo/12270170</a>). As soon as one has deal with such delicate gradient I guess any manual adjusments is noticable. At least I was unsuccessful.<br>

First of all I'd like to understand the nature of this problem. I'm pretty sure that the film photographie does not have such problem. My conlusion so far is this is a digital artifact which is a consequence of either error in RAW conversion or some kind restriction in RAW workflow and I'm trying to push the digital process to hard.</p>

[peterbcarter]

<p>How possible is it to get the raw file, to see for myself? PM me, if you wish.</p>

[Tim_Lookingbill]

<p>Fixed it with custom curve tweak in ACR 4.6. Don't know if your LR version includes point curve tool. You can further adjust saturation and go back and forth tweaking the curve.</p>

<p>It's just a contrast induced banding issue with flat color. Not all camera sensors are entirely linear and Raw converters can't possibly know the exact contrast rendering curve to apply to these types of saturated scenes. You also might try different Camera profiles and create a custom DNG profile for your model of camera and lens combo.</p><div></div>

[alioffe]

<p>Thank you Tim,<br>

I will try later to apply the curve to the complete picture<br>

<a href="../photo/12270170">http://www.photo.net/photo/12270170</a><br>

and see how it is improved.<br>

I have built custom profile using X-Rite passport. It does not help here. I guess the problem may be that the profile is built under certain luminocity. It works well under normal conditions in the middle of the histogram, but at extreme end it is required a different profile because as you mentioned the characteristic is non-linear. So the interpolation method may not work. I have built a few profiles under different conditions (brightness, color cast) and all of them give me a different results. So there is no a single ideal profile for the camera.<br>

My uneducated guess also that any profile is an interpolation. The standard color checker includes 24 colors. It is known that 24-color checker includes a few "popular" colors such as blue sky, skin, green grass and so on. But what about that ones which are not included and may be far away from the color checker? how accurate they are reproduced/interpolated?<br>

Also interesting that such mistake happens on sunrise/sunset conditions and normaly not seen. Google "sunrise" images and dozens images with a similar halo are found.</p>

[michael_b9]

<p>I've been reading this with interest as I do lots of moon shots and constantly struggle with banding.<br>

I've been exporting my raw images from Aperture to PS as tiff files and then been doing curve adjustments there; If necessary to selected areas via masking.<br>

Have never even heard of ACR and am only now beginning to question the possible loss of RAW data somewhere in my workflow<br>

Many thanks! Will try that out! </p>

[Tim_Lookingbill]

<p>ACR=Adobe Camera Raw.</p>

<p>It's a Raw converter that comes with Photoshop starting as far back as version CS, CS2 and up.</p>

<p>I try to do all my edits in ACR which automatically saves them as instructions in the form of an .xmp file that piggy backs with the original Raw image as long as the image remains in a folder. Dragging the image out of its folder to the desktop or to another external volume will lose the .xmp file. Dragging folder to folder retains the .xmp file.</p>

[alioffe]

<p>Tim,<br>

I tried to follow your recommendation in Lightroom. The best I achieved is<br>

<a href="../photo/12291290">http://www.photo.net/photo/12291290</a><br>

Note: there are also other adjusments, which hopefully makes this defect less noticable.<br>

My skills are far away from your level. So a lot things to learn.</p>

 

[michael_b9]

<p>Tim,<br>

thanks for the info!<br>

I will definitely give it a try! <br>

Do you use Lightroom or similar as part of your workflow? I guess part of their idea is to facilitate the workflow but I have found myself moving more towards PS again. Reason being, that I do my high end printing at 'The Printspace' (the name pretty much sums up what it is). This is where I do some final colour tweaking and curve adjustments for their colourspaces prior to converting to an 8bit tiff...</p>

[Tim_Lookingbill]

<p>Alexander, you won't be able to use that exact curve shape posted because it was applied on your gamma encoded jpeg. Since you're working directly on the Raw data you'll have to locate and lock down adjustment points along the posterized/banded sections and tweak each point. It may require some oddly shaped but small pinch curve sections not shown on my posted point curve demo.</p>

<p>Also it needs to be done in ProPhotoRGB and 16 bit output space. ProPhotoRGB's internal 1.8 gamma curve shape has a more gradual slope from mids to highlights so you can spread out the pinch points as well as add more if needed. It's not as hard as you might think.</p>

<p>Just FYI. Your linked image doesn't have an embedded sRGB profile. I don't know if you included it when saving the jpeg, and if so, then the upload process to PN member's portfolios is stripping it. It's been happening to me off and on lately uploading new images to my portfolio. I can tell you for a fact sunset images like yours can REALLY LOOK LIKE CRAP making your banding issue child's play by comparison if not viewed in a color managed app, on a calibrated/profiled display especially on one of the wide gamut variety.</p>

<p>Meike, I don't use Lightroom. Not paying for two applications that pretty much do the same thing. I've budgeted myself to Photoshop upgrades which started in 1998. I find I can do almost everything in ACR to get my Raw images to look as I want. I use Photoshop mainly to add clarity, contrast, sharpening and for downsizing to the web and print.</p>

[alioffe]

<p>Thank you Tim,<br>

for pointing this out. I tried to adjust the curve in LR. In LR this is done in ProPhotoRGB space. Then I moved to PS and converted to sRGB. AFTER CONVERSION THE BANDING INCREASED (easy to see when use "Preview" in conversion dialog).<br>

<em>May be Meike is right: after a certain point - convert to "printing" space and do the rest of adjustments?</em><br>

Then I move to 8-bit mode and saved as jpg. During the saving I the stripped profile.<br>

The posted image on the web in internet explorer looks the same as what I see in PS after conversion. I read somewhere that attaching profile before posting on web (as well as printing in shops) does not make a difference, but only increases size of the file. I guess this is because the web just expect to have sRGB image. But conversion to sRGB is a must. Without conversion it is absoltely not right.<br>

Anyway I'm not satisfied with my result. I will work on this image more and let you review the final result :) Thanks again for pointing me the direction</p>

[Tim_Lookingbill]

<blockquote>

<p>Then I moved to PS and converted to sRGB. AFTER CONVERSION THE BANDING INCREASED</p>

</blockquote>

<p>The only way you would see increased banding converting to sRGB is if you made the image VERY saturated in LR without you knowing it. The only thing that would induce you to do that is if your monitor calibration and profiling is messed up, inaccurate or non-existent.</p>

<blockquote>

<p>During the saving I the stripped profile.<br /> The posted image on the web in internet explorer looks the same as what I see in PS after conversion.</p>

</blockquote>

<p>The fact you said stripping the sRGB profile made the image look the same in Photoshop (a color managed app where CM can't be turned off by stripping the profile) and Explorer (a non-CM app showing colors the same as Assigning your monitor profile to the image in PS) points to a bad calibration and profiling or none at all.</p>

<p>Even if your display's color characteristics were close to sRGB you would still see slight but noticeable differences between Explorer and Photoshop because Photoshop will automatically apply=(Assign) the RGB Working Space chosen in Color Settings to images whose profile has been stripped.</p>

<p>Also your having trouble eliminating the banding in such an easy to fix image suggests something isn't right with your display calibration and profile.</p>