How to use a B&W Image as a Mask

[rbroberts]

In PWP7, this was easy, but I can't figure out the magic to make it work in PWP8.

The documentation says that any B&W image can be a mask. In my case, I'm tying to pick out a small rang of luminosity in the image for some color correction. So the mask I want to create is based on the image itself. For now, I pulled up the image in PWP7 and made my mask and corrections, but I can't figure out the same operation in PWP8.

If this is a RTFM case, can someone point me to the correct location?

Thanks,

roland

[jsachs]

1) I am assuming you have a black and white image that is the same size in pixels as the image it is meant to mask and have opened both of them in PWP 8.

2) Next, select the image you want to change and then select whatever transformation you are planning to use for color correction.

3) Then click the white square at the right side of its Amount control to bring up a menu -- the name of the mask image should appear at the bottom of the menu for you to select. Once you select it, it becomes the initial mask for the transformation, although you can apply additional masking tools to it if you want. When you close the mask dialog box, the color overlay goes away, but you can get the mask dialog back by selecting Re-open mask dialog box from the Amount menu.

4) Make your corrections.

If you wanted to create the mask within PWP 8, you would select New Mask... from the Amount menu instead which brings up the Mask dialog box. Then you could use the Color Range tool or whatever masking tool you want to create the mask.

For more information, download the document Creating and Using Masks.pdf from the Downloads page.

[tomczak]

There is also Mask Transformation, which passes input image to the output image unchanged, but is capable of creating and 'holding' up to four separate masks based on its input image. Those masks can be used in other transformations/images either downstream from the Mask Transformation or in another top-level branch, providing they match the Mask Transformation input image pixel dimensions.

[rbroberts]

3) Then click the white square at the right side of its Amount control to bring up a menu -- the name of the mask image should appear at the bottom of the menu for you to select. Once you select it, it becomes the initial mask for the transformation, although you can apply additional masking tools to it if you want. When you close the mask dialog box, the color overlay goes away, but you can get the mask dialog back by selecting Re-open mask dialog box from the Amount menu.

That's what's not working. When I click on the white square, I don't get a list of black and white images, the menu just says "Help" and "New Mask..." This is PWP 8.0,84.

[rbroberts]

I think I know what's tripping me up, but I don't see how to get around it.

How do I create that black-and white image? With PWP7, it was easy. With PWP8, I've converted a 48-bit color image to monochrome, I'm ending up with an image that, if I save it to disk and reread it in, PWP8 says is 16-bit. I recall masks needing to be 8-bit. But I got 16-bit even though I selected 8-bit on the transformation to monochrome, which is consistent with the manual.

Is the 16-bit B&W what's keeping it from being listed as an available mask? If so, how do I downscale the bit-depth; I'm not finding anything obviously.

[MarkT]

I'm sort of finding the same confusion:

Open an image, make an 8-bit black and white version with High Contrast
On the original image open Levels and Color and open the mask list - newly created black and white image does not appear on list:

new_mask_01.JPG (74.14 KiB) Viewed 4143 times

If I create B&W image, then open a branch from the original image, and then open Levels and Color, the new B&W image does appear on the mask list:

new_mask_02.JPG (79.74 KiB) Viewed 4143 times

[tomczak]

I think that the reason is that the mask is created as an output of the High Contrast transformation - so it doesn't exist upstream from it (otherwise a circular reference would occur).

When you create a side branch, or a new top-level branch, that solves the problem of creating circular references and the mask is visible in those branches, I believe.

Here is a thread that may be useful: https://www.dl-c.com/forums/viewtopic.php?f=4&t=2492

[rbroberts]

I'm sort of finding the same confusion:

Open an image, make an 8-bit black and white version with High Contrast
On the original image open Levels and Color and open the mask list - newly created black and white image does not appear on list:

If I create B&W image, then open a branch from the original image, and then open Levels and Color, the new B&W image does appear on the mask list

Actually, this example is very helpful. Although I've been using PWP for over a decade, I've not really made the jump to v8 very well and I'm still learning how it works. I didn't realize I could create a branch, and if this is the "workaround" to get a B&W image into the workflow as a mask, that works for me.

The confusion is that it's so different from PWP7 that it's not obvious to a newbie with v8 how to create a usable mask. v7 had a special "Mask" menu for creating a mask from an image, and that's what I was trying to accomplish. While the documentation for Mask says "any black and white image can be used as a mask", it should probably say "any 8-bit black and white..." and probably mention that the mask cannot be an image in the same branch as the image you are working on. For astronomical images, which is mostly what I do, it's not true that "the normal way to create a masks is with the mask dialog." It's much more likely that I will use the base image itself as the starting point for the mask (as in I can't remember doing it any other way).

But those two clues (1) 8-bit black and white, and (2) not in the same branch, would at least let me know what I'm missing when trying to create a mask.

[jsachs]

The mask image can be in the same branch -- but it must be above (upstream from) the current transformation. If it is below (downstream) the mask would depend on the transformation that is using it and this would be create an infinite loop. Using a side branch as illustrated earlier in this thread is one way to avoid this. The other, more natural method is to create the mask from within the transformation that uses it via the Mask dialog box and its tool set. This is the PWP 8 equivalent to creating a mask in PWP 7 with the Mask command and then using it in a transformation. The potential problems arise when you use some other transformation (e.g. High Contrast) to create the mask as this requires a side branch to allow everything to happen in the right order.

The help file does already mention this under the Amount control, and the Creating and Using Masks.pdf also describes it, but, for the next release, I have also added a caveat to the topic for Mask, and I have also added an example of using a side branch to resolve downstream mask issues to Create and Using Masks.pdf.

The Convert transformation lets you convert to either 8- or 16-bit black and white via its drop-down menu.

As of recently, 16-bit black and white masks are also supported in PWP 8.

[rbroberts]

Thanks!