What's the Difference Between a Black and Transparent Background?

General Discussion
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1

I often see that most VFX textures have a black background, specifically when there’s no color data (grayscale).
Is there a specific reason for this? Why not just use a transparent background?

One possible reason that comes to mind is that using a black background only requires one channel, which could be useful for channel packing later on.
But if that’s the case, are there any other reasons for choosing a black background over transparency?

2

  1. convenience or the perception of standardizations

  2. reliable thumbnails (files on black is trustable rather than transparency by said software/hardware through time)

  3. the PNG file type full Transparency is encoded as white in Photoshop --suppose it compresses better since RGBA (1,1,1,1)

  4. for the additive blend mode you don’t need Transparency/Alpha and can store this RGB 24bit, and that potentially saved you 8bits - naturally you’d put that texture on black.

  5. For pre-multiplied blend mode the black is expected, hence the term ‘pre’ multiplied (by the source textures Alpha)

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3

Thanks for the detailed explanation!
When using additive and pre-multiplied blend modes, I agree that a black background works well. However, with alpha blending on a black background, those persistent black edges seem unavoidable.
one solution to hide them is to use pre-multiplied blend mode but that will require adjusting both the color and alpha values to fade it completely.
Alternatively, removing the black background entirely is an option to keep using the alpha blend.
But what’s the best approach to handle this issue effectively?

image
image588×789 45.7 KB

Transparent background

image
image586×736 50 KB

Black background

4

‘black borders’ on Alpha blending is because the image was premultiplied by being on black

the concept of transparency is the RGB on your image is at ‘peak’ brightness…maybe this image from Dialbo3 will help describe better

image
this is what the RGB and the Alpha look like to make sure the RGB is not double darkened

ironically for a simple shape that just needs greyscale, image is flat white… Alpha (which is the 1-transperancy) is your shape.

you can open the shape and paste it into alpha to make a selection based on the values
image

then paste a new white layer (delete the old) and re-save as a plain photoshop PNG using transperancy
image

technically this is the RGB you’d use for a simple Alpha blending shape and it is not double dark…

  • it is just white
  • the transparency data functions as the shape
    image

if you dont want a new image and want to reuse the image data…
i forget if ‘Alpha is Transparency’ = False was the fix
but you can alter the alpha blend shader and your frag to just assume (1,1,1) for your texture samples rgb

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5

Thanks a lot Torbach, that clears up the alpha blending confusion!