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Photoshop - Local contrast sharpening etc.

Doug Kerr

Well-known member
Hi, Asher,

I reconstructed this dialog here as it was out of place in the thread on Fahim's work.
==========

You wrote:
I find the shot appealing. You can add a curves layer, just change the blend to "multiply" and then paint into the mask and adjust the percent, for effect.

I wrote, in reply:
Tell me why the multiply blend mode is desirable here.

I'm still interested in that. Further, is that the blend mode for the layer or the blend mode for the paintbrush?

You wrote, in reply:
This picture might benefit from dealing with the bright thin areas to build up the detail and also to ameliorate the lack of local contrast.

Local Contrast Sharpening: It's one of the most useful hidden tricks in Photoshop.

I wrote, in reply:
Well, it remains hidden to me!

I have heard of the concept of local contrast enhancement, done using USM Sharpening (as in fact you describe below).

But here it seems as if you are speaking of doing something like that via an adjustment layer (since you mention using the adjustment layer mask to localize the effect). But I don't know which adjustment layer that is.

I'm still interested in that.

You continued:
It builds up density where one thinks one has really a badly overexposed part of an image. Then one can mask out any part of that one doesn't need. The mask is already waiting for use - it's the white square to the right side of that adjustment layer in the layers dialog box and MUST be selected first by clicking on it! (If not you paint black on your picture, LOL!)

I use a 20% black brush to paint over the actual photoshop picture itself just where one wants to gradually get rid of the increased detail and darkness effect where it's not needed. Every time one releases the mouse and then paints again, an additional 30% of black (i.e., removal), will occur. One can see progress in creation of a black dense area in the little white icon in the layers palette that had been selected before using the brush. So one can very gradually adjust the level of the increased image density.

When it's perfect, go away and have a tea/walk or steal a piece of pie from the refrigerator. When you return, now you can reduce the total effect of that layer on the one below as much as possible and usually it can be down to about 85% or so. You need to always do this to prevent over correcting pictures!

I wrote:
How do I do that?

Of course, duh, I should have known the answer to that: one adjusts the opacity of the adjustment layer on the control bar on the top of the Layers panel with the adjustment layer selected.

But I'm still curious about the matters of the multiply blend mode and "local contrast sharpening" via an adjustment layer.

Best regards,

Doug
 

Doug Kerr

Well-known member
Hi, Asher,

We can of course apply Unsharp Mask in the "local contrast enhancement" vein under control of a (layer) mask.

We just make a copy of the layer to be affected in a layer above, apply the operation to that upper layer directly, and then use a mask on that layer to "let the effect through" into the composite image only where we need it.

Was that what you were thinking of?

Best regards,

Doug
 

Asher Kelman

OPF Owner/Editor-in-Chief
Doug,

There are two separate photoshop tricks!

Local contrast is optimized using unsharp masking and a set of parameters I specified above as ~ 6-12 % and 12-60 pixels wide to then be reduced in the Edit-Fade Unsharp Mask option with "Luminosity" chosen so as to avoid color fringing, the changes being applied ~ as if it were done in the Luminosity channel of LaB space.

Density Build up using "curves" and "multiply" and selective masking : The second and separate procedure is as I described my solution for "thin negatives or transparencies or files with little density of information.

"It builds up density where one thinks one has really a badly overexposed part of an image. Then one can mask out any part of that one doesn't need. The mask is already waiting for use - it's the white square to the right side of that adjustment layer in the layers dialog box and MUST be selected first by clicking on it! (If not you paint black on your picture, LOL!)

I use a 20% black brush to paint over the actual photoshop picture itself just where one wants to gradually get rid of the increased detail and darkness effect where it's not needed. Every time one releases the mouse and then paints again, an additional 30% of black (i.e., removal), will occur. One can see progress in creation of a black dense area in the little white icon in the layers palette that had been selected before using the brush. So one can very gradually adjust the level of the increased image density.

When it's perfect, go away and have a tea/walk or steal a piece of pie from the refrigerator. When you return, now you can reduce the total effect of that layer on the one below as much as possible and usually it can be down to about 85% or so. You need to always do this to prevent over correcting pictures!"

Somehow I didn't make this clear that the two techniques are independent one of the other!

Asher
 

Doug Kerr

Well-known member
Hi, Asher,

Doug,

There are two separate photoshop tricks!

Local contrast is optimized using unsharp masking and a set of parameters I specified above as ~ 6-12 % and 12-60 pixels wide to then be reduced in the Edit-Fade Unsharp Mask option with "Luminosity" chosen so as to avoid color fringing, the changes being applied ~ as if it were done in the Luminosity channel of LaB space.
Sure.

Density Build up using "curves" and "multiply" and selective masking : The second and separate procedure is as I described my solution for "thin negatives or transparencies or files with little density of information.

"It builds up density where one thinks one has really a badly overexposed part of an image. Then one can mask out any part of that one doesn't need. The mask is already waiting for use - it's the white square to the right side of that adjustment layer in the layers dialog box and MUST be selected first by clicking on it! (If not you paint black on your picture, LOL!)

I use a 20% black brush to paint over the actual photoshop picture itself just where one wants to gradually get rid of the increased detail and darkness effect where it's not needed.
Are you sure you don't mean painting on the mask on the adjustment layer? Painting 20% black on the actual image will make it - blacker.

Every time one releases the mouse and then paints again, an additional 30% of black (i.e., removal), will occur. One can see progress in creation of a black dense area in the little white icon in the layers palette that had been selected before using the brush. So one can very gradually adjust the level of the increased image density.

Sounds like painting on the mask to me.

What blend mode is set to multiply? The blend mode for the curves adjustment layer, or the blend mode of the brush?

I can understand that using a brush with a low opacity black, we can "cumulatively" add opacity to the mask, thus gradually diminishing the effect of the adjustment layer where the effect isn't needed.

But I don't understand how the multiply blend mode makes that work.

Thanks for your patience with me.

Best regards,

Doug
 

Asher Kelman

OPF Owner/Editor-in-Chief
Doug,

If you check my original you will see that I indicate that one first selects the white mask box and then does indeed paint inside the actual picture. That's how one designates where one wants the effect to be, but one is actually painting transparency into the mask.

For this, the blend of the curves layer is set to multiply.

The multiply blend just increases the presence of any detail or element in the original image, roughly equivalent to having a bunch of duplicate copies and adding up the densities in each point in the image.

Asher
 

Doug Kerr

Well-known member
Hi, Asher,
Doug,

If you check my original you will see that I indicate that one first selects the white mask box and then does indeed paint inside the actual picture.

Sure.

That's how one designates where one wants the effect to be, but one is actually painting transparency into the mask.

For this, the blend of the curves layer is set to multiply.

The multiply blend just increases the presence of any detail or element in the original image, roughly equivalent to having a bunch of duplicate copies and adding up the densities in each point in the image.
Sure.

Best regards,

Doug
 

Asher Kelman

OPF Owner/Editor-in-Chief
Just in case someone can't find the Edit-Fade Unsharp Mask dialog box option, here is the little secret. One cannot have a mask on the image sharpened and then look for that dialog box as it won't be available. PS assumes then that you are fading the unsharp effect using the mask on that layer. So don't add the mask to that layer until you have globally reduced the unsharp masking with that dialog box set to Luminosity.

Then you can add the mask and remove the effect where you don't need it by painting in black. Limiting adjustments to where they are needed gives the best results.

Asher
 

Doug Kerr

Well-known member
Hi, Asher,

Just in case someone can't find the Edit-Fade Unsharp Mask dialog box option, here is the little secret. One cannot have a mask on the image sharpened and then look for that dialog box as it won't be available. PS assumes then that you are fading the unsharp effect using the mask on that layer. So don't add the mask to that layer until you have globally reduced the unsharp masking with that dialog box set to Luminosity.

Then you can add the mask and remove the effect where you don't need it by painting in black. Limiting adjustments to where they are needed gives the best results.

Good tip. Who would have guessed (but it makes sense, as you explain).

I assume that the you are speaking of applying Unsharp Mask to a copy of the main image layer (and we put the mask there). (I'm still getting used to thinking in those terms!)

Thanks.

Best regards,

Doug
 
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