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Blurring layer mask question

Dec 1, 2012 7:39 PM

I have been trying to figure out for a long time what is going on here, and am stumped.


I have a dark and light layer from the same RAW image. The dark layer is on top.


I create a luminosity mask (Cmd-Opt-click RGB channel) from the light image.

I apply the selection as a layer mask to the top, dark layer.


The detail is bad, looking, maybe, posterized. The image does have lots of fine detail.


When I blur the layer mask, about 40, the image looks great.


****What does the blurring of the layer mask do, to bring out the detail of the image?**** I use layer masks often, and don't usually have to blur to see detail.


I tried to attach/insert a small crop with the 2 layers and mask for you to see, under 2 mb, but the content is not allowed. Hopefully my description will make it easy for you experts.


Thanks for any possble help,



  • Currently Being Moderated
    Dec 2, 2012 1:57 AM   in reply to duck13

    I tried to attach/insert a small crop with the 2 layers and mask for you to see, under 2 mb, but the content is not allowed.

    Then please post screenshots (at Actual Pixels or larger preferably).

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  • Currently Being Moderated
    Dec 2, 2012 10:55 PM   in reply to duck13

    I’m afraid you are just seeing an unfortunate combination of masked content and underlying content.

    With the luminosity mask you are effectively showing the darker image in the lighter regions of the lighter image – so the contrast is being reduced.


    Why are you doing this specifically anyway?

    The lighter image seems to have decent structure and is not blown out.

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  • Currently Being Moderated
    Dec 3, 2012 8:36 PM   in reply to duck13

    Based upon what I'm seeing in the sample provided, the problem is that your darker top layer is proportionally waaay too dark. It is this density that is obscuring detail, not the mask.


    The reason your result is improved upon a high radius blur of the mask is because this bleeds blacks into the whites of your mask, effectively cutting that layer's opacity and effect.


    To wit, if you drop that layer's opacity to 20% or below you wont even need a mask at all. Or at least your normal luminosity mask should serve well enough. Similarly just fill the mask with black and then decrease the mask's opacity (if your version of CS allows this) to 80-90% for similar effect.


    To summarize, your dark layer is simply way to dark to blend convincingly at full opacity with the layer below. Blurring the luminosity mask extensively effectively adds gray to the mask, decreasing the layer's opacity to a more manageable effect.

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  • Currently Being Moderated
    Dec 3, 2012 11:53 PM   in reply to duck13

    I understand what the luminosity mask is doing. I am asking why a perfectly good mask needs to be blurred to bring out the detail.

    It seems you did not fully grasp the issue which is not only about the Layer Mask but also about the underlying and the masked content (which seems not only darker but also less contrasty than the underlying image in your example).


    s.mahn’s explanation seems clearer than my previous attempt, but let me try to add another.

    Say you have one white pixel on 128/128/128 grey in the lower image which corresponds to a 128/128/128 gray pixel on black in a darker second Layer. If a Mask based on the first one’s luminance is used on the second the result is a 128/128/128 pixel on 79/79/79.

    Ergo: less contrast.

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  • Noel Carboni
    23,514 posts
    Dec 23, 2006
    Currently Being Moderated
    Dec 8, 2012 5:13 PM   in reply to duck13

    You're really going to have to attach images here to show exactly what you are seeing.



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