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Hello,

I am new to Photo while have been working with Photoshop many years. I have problems with alpha channels in Photo. My rendered 3D images usually have alpha channel already for backgrounds. Opening them in Photo will show the background 100% transparent. I tried to get the background back by selecting the whole image, creating a spare channel and load this into the alpha channel. This brings my background back but creates white pixels at the borders of my foreground (where alpha isn´t 100% black or white?).

 

test.thumb.jpg.09617f902b3175e150c2662b1ca02a6e.jpg

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Welcome to the forums.
If you just want to put a background behind your isolated image then you can create a rectangle behind the image layer and apply a gradient to that rectangle. Saves messing around with alpha.

Or have I not understood the issue? If not (often happens), is it possible for you to attach the original image?

Annotation 2019-12-15 131212.png

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By selecting the whole image do you mean the object?

It would help if we could download the file and or see the layers panel.

Also which 3D app are you rendering from and in what format PNG? TIF? etc


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It seems to me like the ability to edit channels is very limited in Photo. I cannot edit the alpha channel with anything other than white. This might be part of the problem.

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29 minutes ago, mk3 said:

This doesn´t solve my problem. The white pixels are still there. But I need the original background anyway.

I don't understand. If you need the background, can't you just export it from the 3D app?


Affinity Photo 1.8.4, Affinity Designer 1.8.4, Affinity Publisher 1.8.4;  2020 iMac 27"; 3.8GHz i7, Radeon Pro 5700, 40GB RAM; macOS 10.15.6
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Photoshop renders this perfectly, so when you turn the alpha mask off you get a nice transition from background to product the same thing in Photo gives the effect of a white line but its actually semi transparent pixels.

This is from Photoshop
22585019_ScreenShot2019-12-15at14_54_57.thumb.png.722fc71646d78675090c51db69324760.png

Affinity Photo
1958151137_ScreenShot2019-12-15at14_57_43.thumb.png.7c311095ef6cf0ec515c66d05c43813f.png

There are obviously inherent differences in how Alpha channels are handled, i.e. you can't just turn the Alpha channel off and on you have to fill it, invert it, etc so maybe this action is creating the edge.

The other thing to note is in Photoshop the pixels on the Alpha channel are 100% opaque regardless of the shade but in Affinity there are levels of transparency between shades on the edge.


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I am not sure if it is technically correctly expressed but it appears as if Photo imports the antialiased (transparent) pixels as already rendered values (calculated against white background). If you select the fully opaque pixels (Select > Alpha Range > Select Partially Transparent, and then invert the selection), duplicate that selection and then place it on top of the original Photoshop image with the background, you get identical images.

So it seems that you cannot have either instance of this TIFF file in Photo or other Affinity apps: not one with the background, nor one with antialiased alpha channel that would allow placing the image smoothly blending on any new background. Instead you get an image without a background that can be placed on a white page.

Here is the TIFF image placed on green background in Affinity Publisher:

alpha_tiff_in_apub.jpg.beb9c81c2f34bb846b473a319b4b6c03.jpg

And here the same image in InDesign (where one can choose at import time whether the original background is imported or alpha channel, instead).

alpha_tiff_in_id.jpg.a9fb0a572259185abfef97a966aba3e3.jpg

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You didn't say which App you are using for the 3D render so until then I'll go with Cinema 4D.

In C4D you can add a compositing tag to the object and in the render settings select multipass and add an object buffer. In the save options you can export a mask which masks the background better than using an alpha channel in Affinity Photo.


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Thank you all for your help. Photoshop does this job perfectly and of course there are workarounds with the help of the 3D software. But to be honest: A Photo editing software that cannot handle alpha channel transparency correctly and lacks of alpha channel editing options, does not seem to be an alternative for professional photo editing. At least not for me. Too bad, I would have liked to give Photo a chance. Maybe with a future version.

 

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Would this not do?

Test render.afphoto

This was done with the method mentioned earlier.

Screen-Shot-2019-12-15-at-22-59-27.png
Screen-Shot-2019-12-15-at-22-59-38.png


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These are the files used.

Untitled.tif

1534171823_UntitledMP_object_1.png.6aa7550fb70f4bbc446b1efddc40cd35.png


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I did some further examination and it seems that the way the transparency is handled here is called "non-premultiplied (or straight) alpha", that is, transparency information is expressed separately in alpha channel. Affinity apps, however expect the transparency to be expressed "premultiplied" in RGB channels, matted against a background color (typically black or white). Many professional apps allow specify at import time, how the alpha (transparency) should be interpreted, and support both methods (and specifying the matte color that is used for color dematting, if needed).

Basically it does not matter which method is used as long as the rendering app knows how transparency information is saved, but obviously there is typically no meta data to tell this, even if the app supports both methods, so this is a manual setting e.g. in GIMP and After Effects.

EDIT: Affinity apps do support "straight" alpha e.g. with PNG images, so it is a question of providing an option when opening/importing a TIFF image, which can have either kind of transparency (as can have some other image formats, as well). Deducing the method used is not reliable so the option normally needs to be made explicit.

The method of both including the background, and removing it by using a separate transparency data in alpha channel, is highly efficient, but it seems that very few apps can actually use either of the image instances: CorelDRAW and Inkspace e.g. can interpret straight transparency [of this specific TIFF file] correctly but do not offer an option to ignore the alpha channel. Scribus interprets the file correctly but ignores the alpha channel when exporting to PDF (but correctly handles it when exporting to bitmaps). QuarkXPress (2018), on the other hand, simply just ignores the alpha channel and reads in the background, and Affinity apps expect the TIFF  transparency to be expressed premultiplied and import the image without the background but without calculating the transparency against the current background, which leaves a fringe at semitransparent areas when the image is placed against non-white background.

More information on the subject can be found here:

https://www.provideocoalition.com/alpha-channels-premultiplied-vs-straight/ 

https://helloluxx.com/tutorials/after-effects-2/after-effects-compositing/straight-vs-premultiplied-understanding-alpha-channels/

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Excellent info @Lagarto and makes sense from what I've seen. 

It's this kind of information that should be in the help files or an "advanced" help file with this level of technical information.


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25 minutes ago, firstdefence said:

It's this kind of information that should be in the help files or an "advanced" help file with this level of technical information.

Yes, it would be very useful to have details of things like color management and image manipulation (algorithms / alpha channels) documented to some extent. I suppose they are discussed in video tutorials, but often there is no time to watch long videos simply to find out more about technicalities.

Alpha channels are important specifically in 3D editing where a background and lighting are carefully composed but where the object itself is also wanted to be extracted and smoothly integrated for different purposes (e.g., for catalogues), so it is clear that this kind of file format which can save and offer both options is very useful. Hopefully it will be soon supported also in Affinity apps.

As for alternative methods, was the version you provided above (alpha transparency used as a mask) directly exported from a 3D app (Cinema 4D?), or did you manually create the mask?

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1 hour ago, firstdefence said:

It's this kind of information that should be in the help files or an "advanced" help file with this level of technical information. 

Absolutely!

39 minutes ago, Lagarto said:

Yes, it would be very useful to have details of things like color management and image manipulation (algorithms / alpha channels) documented to some extent. I suppose they are discussed in video tutorials, but often there is no time to watch long videos simply to find out more about technicalities.

Absolutely again!

For numpties like me using Affinity, the only way to glean extra information when using these apps is to spend hours each week sifting the forum for hopefully relevant nuggets.

Sure it has by necessity become my new hobby ^_^, but it's not an efficient use of work time.


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1 hour ago, Lagarto said:

As for alternative methods, was the version you provided above (alpha transparency used as a mask) directly exported from a 3D app (Cinema 4D?), or did you manually create the mask?

Created in C4D using a render tag: composite on the object and then specifying an object buffer under render settings.

880118467_ScreenShot2019-12-16at09_23_03.png.09cd6e7a72def9efe6eb0e5e08eeea34.png

221432908_ScreenShot2019-12-16at09_27_50.png.1338eeac27f0af878e99f106a27be9c4.png


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17 minutes ago, firstdefence said:

Created in C4D using a render tag: composite on the object and then specifying an object buffer under render settings

Interesting. This seems to be an efficient and compatible way to handle complex post-product scenarios. Standard single images with straight and separate alpha seem to be available, as well, so I suppose there are often ways to adjust one's workflow to meet specific needs, so we need not be so badly dependent on specific software. 

Personally my 3D needs are modest and more than exhaustively covered by Blender, but this seems definitely a very sophisticated package! 

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Yes, C4D is up there with the best of them, I tried blender but just couldn't get along with it, but for a freebie it's off the chart awesome.


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1 hour ago, Roger C said:

Sure it has by necessity become my new hobby ^_^, but it's not an efficient use of work time.

No, this sometimes badly interrupts works! But it is efficient for learning to use three new apps, finding out what can and cannot be done with them, and (slowly) becoming confident that they can become alternative production tools. In addition, one learns much useful also about other apps and new and more effective ways of doing old things!

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1 hour ago, Roger C said:

For numpties like me using Affinity, the only way to glean extra information when using these apps is to spend hours each week sifting the forum for hopefully relevant nuggets.

Or you could just start a new topic in the appropriate sub-forum with a descriptive title & a clear explanation of what info you are looking for.


Affinity Photo 1.8.4, Affinity Designer 1.8.4, Affinity Publisher 1.8.4;  2020 iMac 27"; 3.8GHz i7, Radeon Pro 5700, 40GB RAM; macOS 10.15.6
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What about a Tips & Tricks sub-forum?


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23 minutes ago, firstdefence said:

What about a Tips & Tricks sub-forum?

Tutorials?


-- Walt

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iMac 27" Late 2015 Fully Loaded, iMac 27" Mid 2011 both running High Sierra 10.13.6 - Affinity Designer/Photo & Publisher - Illustrator CC, Inkscape, Blender, Sketchup, Pepakura Designer, MTC, Pixelmator & Pixelmator Pro + more... XP-Pen Artist-22E, - iPad Pro 12.9 B|  

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1 minute ago, firstdefence said:

That's what I pointed to, firstdefence :)

I was suggesting that it is already a sub-forum for Tips & Tricks.


-- Walt

Windows 10 Home, version 2004 (19041.388),
   Desktop: 16GB memory, Intel Core i7-6700K @ 4.00GHz, GeForce GTX 970
   Laptop:  8GB memory, Intel Core i7-3625QM @ 2.30GHz, Intel HD Graphics 4000 or NVIDIA GeForce GT 630M
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