Contrast masking and Gaussian blur

PE
Posted By
phoney.email
Apr 10, 2004
Views
312
Replies
2
Status
Closed
I’m currently busy contrast masking in order to boost the (very!) limited dynamic range of my film scanner. This involves scanning the same slide twice, once for highlights and once for shadows. The two scans are then stored in layers and the bottom layer is used as the layer mask for the top layer, resulting in an image composed of the best parts of both.

During this procedure a certain amount of Gaussian Blur should be applied to the layer mask.

Now then, there are basically two distinct cases here: one, when an image mostly comes through (highlights scan supplies the highlights, shadows scan supplies the shadows), and two, the "bit in the middle" where both layers contribute.

The problem is, case one (an image comes through) wants minimum, read *no*, Gaussian blur while case two (the mix) wants *lots* of Gaussian blur.

Choosing the "happy medium" of Gaussian blur just makes them both unhappy… Case one develops "auras" while case two becomes washed out.

I could edit the layer mask manually but that’s far too time consuming and finicky, and I’m trying to streamline and automate the procedure as much as possible.

Any ideas on how to do that?

Don.

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BV
Bart van der Wolf
Apr 10, 2004
"Don" wrote in message
SNIP
I could edit the layer mask manually but that’s far too time consuming and finicky, and I’m trying to streamline and automate the procedure as much as possible.

Any ideas on how to do that?

Did you try the Layer blending options (in CS it’s Layer|Layer Style|Blending Options…), in particular the Blend if: sliders. You only want to blend in the better defined shadows which are lacking in the highlight scan. Assuming the shadow scan as the top layer, you drag the "Underlying Layer" highlight point way down to where the shadows are lacking in the highlight scan. Then with ALT you pull the lower half of the same highlight marker to (close to) zero for a smooth transition. This will only be *really* successful if you adjusted the shadow scan’s luminosity by dividing the linear gamma Raw scan data by the increased exposure factor. Once you’re done you can gamma adjust the composite (an adjustment layer comes in handy if you want to maintain the individual layers).

Bart
PE
phoney.email
Apr 10, 2004
On Sat, 10 Apr 2004 13:08:38 +0200, "Bart van der Wolf" wrote:

"Don" wrote in message
SNIP
I could edit the layer mask manually but that’s far too time consuming and finicky, and I’m trying to streamline and automate the procedure as much as possible.

Any ideas on how to do that?

Did you try the Layer blending options (in CS it’s Layer|Layer Style|Blending Options…), in particular the Blend if: sliders. You only want to blend in the better defined shadows which are lacking in the highlight scan. Assuming the shadow scan as the top layer, you drag the "Underlying Layer" highlight point way down to where the shadows are lacking in the highlight scan. Then with ALT you pull the lower half of the same highlight marker to (close to) zero for a smooth transition. This will only be *really* successful if you adjusted the shadow scan’s luminosity by dividing the linear gamma Raw scan data by the increased exposure factor. Once you’re done you can gamma adjust the composite (an adjustment layer comes in handy if you want to maintain the individual layers).

Yes, I did try Layer Blending but gave up because I was getting results similar to contrast masking with no Gaussian blur i.e. I had problems with the midrange. Also it ended up taking a lot of time.

However, with the extra tips you mention above I’ll have another go! Thanks!

Don.

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