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When flatten image yellowish blotch appears

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  #21  
Old 09-17-2014, 11:11 AM
John Wheeler's Avatar
John Wheeler John Wheeler is offline
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Re: When flatten image yellowish blotch appears

Hi Nebual and all
Very interesting discussions. Here is my take (and I am guessing on the issue of the original issue).

I suspect (guessing) that the detail in the texture of the subjects top is higher than the resolution of the digital sensor you are using. At that point a number of artifacts can occur which also depends on the Raw converter - demosaicing algorithm used.

Several that I not in the image I see are so non color Moire, maize artifacts and most predominantly stippling where adjacent pixels are very high in contrast though that does not really exist in the real subject.

When you have this high contrast adjacent pixels, the unsharpen filter identifies those areas to increase the contrast more. The unsharpen filter can both desaturate and shift hue in the areas it changes.

There are more sophisticated ways to get around this problem yet for the areas where you have the problem, use the despeckle filter before applying sharpening (minimizes the adjacent high contrast pixels) and turn up the Threshold slider so that sharpening is applied less to the lower contrast areas and focuses the sharpening in the higher contrast areas.

Some actually like the stippling they see as it gives a feel of crispness or chrunchiness even if they are artificial. You have come across one of the downsides of such artifacts when using the unsharp filters.

This is also why the issue occurs in the in-focus areas. Out of focus areas don't have the detail to cause the anomalies in the first place.

Other sharpening filters (e.g. smart sharpen) have more controls for highlights and shadows yet all sharpening filters to some level if you leave the artifacts in while doing the sharpening.

Of course this is just my best guess looking at the data supplied so this may or may not be your root cause issue. Hope the info is of some use.

ADDED EDIT - I do not believe this particular artifact is caused by issues with merging/flattening or magnification level viewing even those certainly could make things worse. View a fully merged image at 100% to make sure those are not adding in to the issue yet this time I think the issue is the artifacts in the original image data. IMHO of course
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  #22  
Old 09-17-2014, 11:41 AM
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shift studio shift studio is offline
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Re: When flatten image yellowish blotch appears

Quote:
Originally Posted by nebulaoperator View Post
Bingo! It did a job. I compared both : sharpening claw layer filter>unsharpen and HF layer in split . Higher frequency is not effected by yellow blotch.
Many Thanks
I'm glad that worked for you.

--shift studio.
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  #23  
Old 09-17-2014, 02:17 PM
klev klev is offline
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Re: When flatten image yellowish blotch appears

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Originally Posted by shift studio View Post
I admit I have only skimmed this thread (all you can do when skoobey and klev are posting ) ...

Maybe a solution is an asymmetric frequency split, then apply your unsharpen filter on only the high frequency layer - or something like that.

-- shift studio.
Hah! I'll admit I am somewhat long winded. The advice can also be somewhat generic when I don't have the ability to go through an image and pick apart what would have added up to that.
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  #24  
Old 09-18-2014, 10:29 AM
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mistermonday mistermonday is offline
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Re: When flatten image yellowish blotch appears

There are two things to watch out for when you are working with layers in PS especially when you have more than one adj layer. Sometimes the sequence of how the layers are merged when an image is flattened is important. PS has a set of criteria for sequencing but the sequence will sometimes result in results which are not visually the way you intended them to be.
The other thing to be aware of is that PS has some "quirks" in how it displays an image. Remember that when you have a layer stack, and the image has a large number of pixels, PS is only displaying a sampled and extrapolated preview to you of the final result. And all of those filters and adj layers are actually NOT applied until you flatten or print the image.
Here is a link to a simple real world demonstration of the image preview problem, which by the way has been well known for many generations of PS versions.
Before you open the tiff file at the link below please read the following:
- For the purposes of this demo, it is important not to alter the image in any way so that means NOT changing its color space which is sRGB. So if your PS workspace is sRGB, then you do not need to do anything. But if your workspace is AdobeRGB or any other workspace make sure your Edit>Color Settings either has the Profile Mismatch Warnings enabled or that it is set to "USE THE EMBEDDED PROFILE" and does not convert the image to your working color space.
- Open the file. It will appear totally white to you, that's OK.
- Type Control L to bring up the Levels Command Dialog window.
- Grab the Gamma (Center) triangle and drag it all the way to the very right, right to the very end. Yes, the image will look weird.
- Next grab the Shadow triangle at the far left and drag it all the way to the far right as well, right to the very end. An image will form and it will look very strange. That's all right as well.
- Take a good look at the image. Now click the OK button to complete the Levels command.
- You went from preview to final application. What happened?

Now go back and start over again but this time instead of the Levels command, use a Levels Adj Layer. Add the levels adj layer on top of the background. Next make the two adjustments with the sliders in the same sequence as above. Your image should look pretty strange. After you take a good look at the image, make sure the Levels Layer is active and hit command E to merge the layer down (flatten). Here is where the fun begins. The image may look normal or it may not have changed. If it has changed, zoom in and out from 12.5% thru 50% and you may see the image toggle back and forth between the final view and the preview. If the image did not appear normal after
you flattened it, just hold the Alt key down and double click the background layer to convert it from a background to an actual layer. Now what do you see.

I have one last comment regarding your yellow blotch. In PS, while the previews often lie, colors rarely if ever do. So you should always move your eyedropper tool around suspect areas to see what the pixel values read. Having your secondary sampler in the info palette set to LAB color will allow you to immediately identify a color of the region. You might need to switch the sampler from single pixel to 3x3 or 5x5 depending on your image size.
http://www.mediafire.com/view/9sn13k...er_Exposed.tif
Cheers, Murray
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  #25  
Old 09-18-2014, 03:14 PM
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nebulaoperator nebulaoperator is offline
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Re: When flatten image yellowish blotch appears

At John,
,,The unsharpen filter can both desaturate and shift hue in the areas it changes.,,
,,There are more sophisticated ways to get around this problem yet for the areas where you have the problem, use the despeckle filter before applying sharpening (minimizes the adjacent high contrast pixels) and turn up the Threshold slider so that sharpening is applied less to the lower contrast areas and focuses the sharpening in the higher contrast areas.,, I like these suggestions of yours John In fact I had despeckle filter too prior to unsharpened filter but then it would defeat the purpose. Split frequency got me excellent results.
Was image faulty at the start? Maybe. However I did use unsharpen filter on just out of the ACR image and there were no desaturation/yellowishness observed.
,, I do not believe this particular artifact is caused by issues with merging/flattening,, some conditions in the chain were the cause to my issue however only flattening revealed them.
Thanks
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