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,
Hopefully this will work. Here is the link to the file, including the 2 layers, and layer mask, cropped.
To summarize, why is it necessary to blur the layer mask ( ~40) in order to see detail?
The mask is a luminosity mask (Cmd-Opt-click RGB channel) created from the light layer, and then applied to the dark layer.
As I mentioned originally, I use layer masks often, and don't have to blur the mask, unless I want a special effect. It seems that whenever I blend this way, with a luminosity mask, the mask has to be blurred.
Correction from original post: each layer is a separate camera exposure, then processed in Lightroom.
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.
Yes, in ths case, the dynamic range looks fine, as I have submitted a very small crop, excluding the very bright pixel. That part is not necessary to demonstrate the luminosity mask, and my question.
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. After blurring the mask, it works fine. What is the reason for poor detail prior to blurring?
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.
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.
Thanks to both of you for jumping in and taking the time to explain. I have been away, and now will have time to digest your helpful explanations. Unfortunately, the crop does not show the bright part of the layer, which necessitated the blending. I could include that part, but, first I should study your helpful explanations. If I am still confused, I will submit the part of the image which is bright, and ask for your comments.
I really appreciate your help,