Possible to show correct histogram with mask turned off?

[Guy Burns]

I have a PSD file with several Curves layers to adjust contrast and colour. Without a mask, each layer correctly shows the histogram after all lower adjustment layers have been applied. However, when I add a Mask to a layer the histogram reflects the effect of the Mask, even if I turn the Mask off.

To see the correct histogram with the Mask turned off, I have to delete the Mask. An example file is attached.

Is there a way to tell PS to display a histogram without the effect of the mask?

[c.pfaffenbichler]

The attachment fails to download, please post meaningful screenshots on the Forum directly. 

If an Adjustment Layer has a Layer Mask it would not seem surprising that the resulting Histogram was different for with/without the Mask, so please explain in more detail. 

[Guy Burns]

Thanks for the response. I thought nobody had responded, since I didn't receive an email.

I just tried the attachment and it downloaded okay. Screen shots would not really show the problem. If the attachment can't be downloaded by others, I'll upload to MediaFire.

Here are more details about the problem, with reference to the attachment. It will be difficult to explain the process, but I'll give it a go.

1. I use several adjustment layers so that I have fine control over each. Curves 1 adjust for maximum contrast without loss of levels. I could apply further adjustments within Curves 1, but fine control is lost, so I add Curves 2.
2. Curves 2, which shows the histogram with Curves 1 already applied, starts as a straight line. By looking at the histogram shown within Curves 2, I can make further contrast adjustments as required. For example, I decided that BC301 (a B&W negative taken in 1947) needed to have darker shadow areas, so based on the histogram, I lowered the curve in the shadow area so that the straight line section roughly parallels the rise in the histogram. Experience has taught me that doing so is a good starting point. Lowering the shadows has improved the contrast in the rest of the image (important for the people in the photo), but it also means shadow detail has been lost.
3. To correct for lost shadow detail, I generate a mask on Curves 2 that selects a certain amount of the shadows. I do that via an Action which brings the Threshold layer into play tempororily, I adjust the Threshold, and then the "action applies the mask.
4. Then I adjust the Density and Feathering of the mask, to make sure the shadows have depth but are also showing a suitable amount of lost detail. Note that the mask can only deepen the shadow areas (by lowering the Density).
5. Sometimes Step 4 hasn't fully recovered the lost shadow detail. To remedy that, the Action also adds the Curves 2 mask to the Shadows layer (but inverted) to enable me to bring out the shadows even further by adjusting the curve in the Shadows layer. This was not necessary in BC301, so I have deleted the Shadow layer mask in the attachment.

The problem for me is, once the mask is added to Curves 2, is that I can't see the real histogram coming in from Curves 1. In the attachment, the histogram for Curves 2 (with the mask active or not) is truncated and starts at about level 50, whereas without the mask it goes down to 0.

A truncated histogram makes it more awkward to make further adjustments to Curves 2 – if I need to.

The workaround is to move the mask to another layer above, as a temporary store while I adjust Curves 2.

[c.pfaffenbichler · Accepted solution]

Why don’t you apply the Layer Mask to a Group and put »Curves 2« in the Group? 

[Guy Burns]

Thanks. Another correct solution.