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LenC

AP: Why does new mask have a transparency checkerboard?

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I'm trying to learn about using channels for blending or masking to darken a sky. I selected my background layer and executed Background Blue channel: Create mask layer. The new mask layer appears as in the attached file, with a checkerboard all over the image. The blue channel is supposed to be 256 shades of gray, not an alpha channel. (My document menu has Transparent Background checked, presumably a default, as I don't know what this means.) In any case, if I nest the mask in the background layer it appears as the blue channel and does what it is supposed to do, permitting me to blend-Multiply-darken the sky without darkening the foreground. Can someone clarify what is going on or where I can read more about this?

Also after importing a JPEG, the Channels panel always shows a Background alpha channel, which can't be there (I think). Bug, or feature of which I am ignorant?

Screen Shot 2019-01-24 at 6.29.30 PM.png


AP 1.7.3, MacOS 10.14.6 (usually latest of each, but not going to Catalina until more issues are resolved)

Mac Mini, Late 2012, 2.5 GHz Intel Core i5, 8 GB; HD replaced with SSD

 

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Hi @LenC,

When you create a mask from the blue channel, it will mask your image based on the black/white/gray in your Blue channel, thus creating the alpha channel. Since you have a transparent background, you will see the checkerboard. I'm not really sure why you think this is a bug unless I misunderstand the issue. 

Thanks,

Gabe. 

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Thanks, I guess my puzzlement is just because I never saw this before, and it does begin to make sense. I have created masks as part of adjustment layers for a couple of years and never (IIRC) saw this checkerboard before. I get it that a mask and an alpha channel are two aspects of one type of algorithm, but not sure when the different names apply. The mask above the layer shows the checkerboard plus what's visible in the layer below, but nested with the layer it shows no checkerboard, or just the blue layer if I click the thumbnail. But the Channels panel has added a Mask Alpha channel. I will have to check if other masks have a Mask Alpha channel.

The bug question was separate. I thought that all JPEGs do not have an alpha channel by their 3-byte design ; is this right?  But the Channels Panel has a layer (empty) labeled Background Alpha. This would make sense to me if importing a file with an alpha layer, but not if it does not exist.

I will be exploring the issues with channel behavior and UI in AP that others have pointed out in these forums.

 


AP 1.7.3, MacOS 10.14.6 (usually latest of each, but not going to Catalina until more issues are resolved)

Mac Mini, Late 2012, 2.5 GHz Intel Core i5, 8 GB; HD replaced with SSD

 

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42 minutes ago, LenC said:

I thought that all JPEGs do not have an alpha channel by their 3-byte design ; is this right?

That's correct. But once you import the image, the software does not limit you to just RGB. It creates the Alpha channel automatically (blank if jpeg).

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JPEG is a method of encoding an image when it is saved onto disk. Once you open it in a photo editor (any editor) it is just an array of pixels initially in just one layer plus, as @GabrielM says, an Alpha channel. It is only when you export that it becomes a jpeg (or whatever file format you choose).

John


Windows 10, Affinity Photo 1.7 and Designer 1.7, (mainly Photo), now ex-Adobe CC

CPU: AMD A6-3670. RAM: 16 GB DDR3 @ 666MHz, Graphics: 2047MB NVIDIA GeForce GT 630

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Thanks to both. Just a little more: how do you create that link to a particular member like @GabrielM?


AP 1.7.3, MacOS 10.14.6 (usually latest of each, but not going to Catalina until more issues are resolved)

Mac Mini, Late 2012, 2.5 GHz Intel Core i5, 8 GB; HD replaced with SSD

 

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51 minutes ago, LenC said:

Thanks to both. Just a little more: how do you create that link to a particular member like @GabrielM?

I just type @LenC slowly and then click on the name in the list which appears below. Perhaps your browser doesn't allow the list to appear.


MacBook Pro (13-inch, Mid 2012) Mac OS 10.12.6 || Mac Pro (Late 2013) Mac OS 10.14.5

Affinity Designer 1.7.3 | Affinity Photo 1.7.3 | Affinity Publisher 1.7.3 | Affinity Designer Beta 1.7.x.x | Affinity Photo Beta 1.7.x.x | Affinity Publisher Beta 1.8.0.499

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On 1/25/2019 at 3:13 AM, GabrielM said:

Hi @LenC,

When you create a mask from the blue channel, it will mask your image based on the black/white/gray in your Blue channel, thus creating the alpha channel. Since you have a transparent background, you will see the checkerboard. I'm not really sure why you think this is a bug unless I misunderstand the issue. 

Thanks,

Gabe. 

This is all confusing and I don't feel like the question was answered. Can a mask layer be applied with seeing the checker board 

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5 minutes ago, cdw86 said:

This is all confusing and I don't feel like the question was answered. Can a mask layer be applied with seeing the checker board

You cannot reply to this with yes or no. It depends on other factors:

If you have transparent background on or off. 

If you have any other layers behind the current layer. 

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The transparent background in unchecked now the mask is all white instead of all white with checkboard over it? 

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Presumably you have created a basic white mask. Depending on what you want to do, you may want to make some black selections on it. If your question is more specific and contains some more details and is posted on the main forum page, you will get better help.

I would go over the selecting and masking video tutorials

Also look up masks in the online help

https://affinity.help/photo/en-US.lproj/index.html

If you are looking for a text introduction, there is a new inexpensive one by Robin Whalley that you can find through Google.


AP 1.7.3, MacOS 10.14.6 (usually latest of each, but not going to Catalina until more issues are resolved)

Mac Mini, Late 2012, 2.5 GHz Intel Core i5, 8 GB; HD replaced with SSD

 

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