Mask Mode really should be Mask Display Mode?

[Nocturnal]

Hi,

I have to admit I've been a bit baffled by the recent addition of Mask Modes. I couldn't really imagine why anyone would want to replace the red channel with a mask or use any of the other colors. I would always set it to multiply as that is what I want the mask to do and then stop showing the mask. So I re-read the release information for the releases where this was added and now I understand that Mode really doesn't do what the name suggests. I merely changes the way a mask is *displayed* not what it actually does.

In light of this I want to suggest that the menu be renamed to Display Mode or simply Display.

Let me know if I still don't understand this menu item.

[Simon Hicks]

I much preferred it when it just had the one mode, and I didn't have to change it to "multiply" every time. It could be just a preference thing?

[Juan Conejero]

Hi Sander,

I fully agree with Display instead of Mode, or "mask display mode", depending on the context. Thanks for the suggestion, I'll make the change in the next version.

why anyone would want to replace the red channel with a mask or use any of the other colors.

The red channel isn't replaced on the screen. The mask is displayed as an "overlay" —just as if the mask were a monochromatic, translucent film layer placed on top of the image.

An overlaid mask representation has some important advantages over the classic multiplicative representation (classic in PI, of course). With an overlaid mask, you can see the true protection effect of the mask on all parts of the image. With a multiplicative representation, dark or bright areas cannot be represented correctly, depending on the mask used. For example, this is a big problem with deep-sky images using noninverted masks, mainly because low values (the sky background) multiplied by low values (the sky in the mask) are much lower values. With inverted masks, the same happens for bright areas. This never happens with overlaid masks.

The different colors are there because depending on the image, a particular mask color can be useless. For example, a red mask representation is bad for an image where the red color dominates. The particular colors offered as mask display modes (red, orange, etc.) cover virtually all possible cases, and can be implemented with very efficient code by PI's screen rendering engine.

[Juan Conejero]

Simon,

and I didn't have to change it to "multiply" every time. It could be just a preference thing?

It's already in preferences:

- Select Edit > Global Preferences from the main menu.
- Select the Default mask settings section on the GlobalPreferences interface.
- Select the desired default mask rendering mode.
- Press F6 (or click the blue ball) to apply the process globally.

[Nocturnal]

Hi Sander,

I fully agree with Display instead of Mode, or "mask display mode", depending on the context. Thanks for the suggestion, I'll make the change in the next version.

why anyone would want to replace the red channel with a mask or use any of the other colors.

The red channel isn't replaced on the screen. The mask is displayed as an "overlay" —just as if the mask were a monochromatic, translucent film layer placed on top of the image.

An overlaid mask representation has some important advantages over the classic multiplicative representation (classic in PI, of course). With an overlaid mask, you can see the true protection effect of the mask on all parts of the image. With a multiplicative representation, dark or bright areas cannot be represented correctly, depending on the mask used. For example, this is a big problem with deep-sky images using noninverted masks, mainly because low values (the sky background) multiplied by low values (the sky in the mask) are much lower values. With inverted masks, the same happens for bright areas. This never happens with overlaid masks.

The different colors are there because depending on the image, a particular mask color can be useless. For example, a red mask representation is bad for an image where the red color dominates. The particular colors offered as mask display modes (red, orange, etc.) cover virtually all possible cases, and can be implemented with very efficient code by PI's screen rendering engine.

Hi Juan,

thanks for considering this small change that I hope will clarify what the option does. As I wrote I figured out today that the overlay really does not indicate what the mask does but only a way to indicate where the mask is in effect. But thanks for explaining further what it's for.

The way I judge a mask's effectiveness is by disabling and enabling it in the RTP window. I never 'show' the mask so I never saw the need for red or green masks. I'm sure it's useful though.

[Simon Hicks]

Simon,


Quote
and I didn't have to change it to "multiply" every time. It could be just a preference thing?

It's already in preferences:

- Select Edit > Global Preferences from the main menu.
- Select the Default mask settings section on the GlobalPreferences interface.
- Select the desired default mask rendering mode.
- Press F6 (or click the blue ball) to apply the process globally.

Thank you Juan!

[Nocturnal]

Now that I know what the 'mode' really does I see the value of the various colors. The thing is that it seems the overlay is shown in reverse. I imagined the redder parts would show where the process would be applied rather than how it is right now. In other words I expected white in the mask to be red in the overlay. It's the other way around. I think I'll set the default to 'multiply' as that shows the data that will be processed. I thought about requesting a 'reverse overlay' option but that could be very confusing so we should leave it as is. Well, with the name change of course