Participant

Answered

Png not opening with alpha channel

Forum|Forum|7 years ago
May 13, 2018
7 replies
20103 views

photoshop incorrectly opens pngs with transparency instead of using a proper alpha channel.

this is a long standing bug any word as to why it has not been corrected?

This topic has been closed for replies.

Correct answer davescm

The issue is not with opening PNGs but with saving them. . The PNG format allows transparency to be saved two ways - 1. A colour indexed to be transparent and 2. A separate Alpha channel.

Photoshop saves PNGs with transparency rather than separate Alpha

On opening you can easily get the Alpha channel back using Layer - Layer Mask from Transparency

Dave

rayek.elfin

Legend

It's not only VFX artists who have to deal with this. Game developers/artists have similar problems in game engines. For example, I use Godot, and Godot actually expects these issues, and automates the process to fix it. Because Photoshop is not the only image editor to export PNGs like this.

https://docs.godotengine.org/en/3.0/getting_started/workflow/assets/importing_images.html#process

Btw, about that premultiplied PNG method: Color Quantizer has an option to optimize the alpha for black, white or any other custom colour. By right-mouse clicking the image area, other options appear to handle alpha (such as splitting the translucent pixels from the opaque ones).

Color quantizer free download

P

Philip25697023ry6h

Participant

For anyone else frustrated at Photoshop only handling PNG transparency and not true alpha channel, the good news is that there is a great open-source plugin https://www.fnordware.com/superpng/ which allows for reading and writing of alpha OR transparency from PNG files, plus much more.

In the context of the discussion above, it allows use of PNG alpha without affecting the colour values of non-opaque pixels, which is exactly what is needed in many game-development and 3D pipelines.

L

lizlizlizlizlizliz

Participant

Just wanted to thank you for this comment-- I'm here over a year later looking for a solution to this, and it seems like this plugin will be super helpful. Cheers!

Daniel E Lane

Inspiring

Seems that a lot of people do not understand the difference between an Alpha Channel and Transparency. One is additive and the other is Subtractive. Big difference.

T

tripsanAuthor

Participant

chris and i have disagreed for quite some time on this one.

as far as an example goes this isn't a specific problem with a file. its a problem with an implementation of a format.

Jeff Arola

Community Expert

Can you explain the underlying issue as you see it?

T

torbach

Participating Frequently

Sorry for not creating a post for you Jeff

the issue

authoring png pixels with color + alpha channel value of 0 is impossible

the only way to have an alpha channel native in PS(2019) is delete the pixels in the layer (not use alpha channel) and then perform a PNG save.

But then color data for empty pixels is white...

cannot have color and alpha 0

[no quick_export; this performs a trim function]

I cannot stress this enough... web/mobile/AR_VR or just Real-time VFX industry that uses PNG format for small file sizes and RGBA do not utilize SuperPNG because we are biased/hacks .

we, in fact, need its capabilities - simple.

Jeff Arola

Community Expert

Maybe you could post an example png and what other application, if any, besides photoshop you want to use the png in.

Also, the version of photoshop and operating system your using.

T

tripsanAuthor

Participant

fair point. i suppose what i meant to say is Photoshop incorrectly opens and saves Png files. the png specification isnt supported correctly.

the layer mask from transparency is hacky and ultimately does not deal with the underlying issue.

D Fosse

Community Expert

Alpha = transparency wouldn't work in Photoshop. Alpha channels are used for much more than transparency, primarily to store selections. But it can be used for anything - it's basically just an extra channel.

As for the PNG specification, former PS engineer Chris Cox (who used to post here) always insisted that Photoshop was doing it correctly according to spec, the others took shortcuts with the specification. Yes, this has been discussed many times before.

davescm

Correct answer

Community Expert

The issue is not with opening PNGs but with saving them. . The PNG format allows transparency to be saved two ways - 1. A colour indexed to be transparent and 2. A separate Alpha channel.

Photoshop saves PNGs with transparency rather than separate Alpha

On opening you can easily get the Alpha channel back using Layer - Layer Mask from Transparency

Dave

T

torbach

Participating Frequently

Unacceptable; VFX artists in particle systems often use Premultiplied Alpha Blend mode

Source: One

Destination: OneMinusSrcAlpha

Transparency save/quickExports destroy RGB

open PNG pixels {rgba} 32,32,255,0

users do not want to open this and see plain white --- We don't use SuperPNG because it is trendy, it is because we need the tool.

thanks for listening

davescm

Community Expert

wrote
Unacceptable; VFX artists in particle systems often use Premultiplied Alpha Blend mode
Source: One
Destination: OneMinusSrcAlpha
Transparency save/quickExports destroy RGB
open PNG pixels {rgba} 32,32,255,0
users do not want to open this and see plain white --- We don't use SuperPNG because it is trendy, it is because we need the tool.
thanks for listening

Hi

We are not Adobe employees here - just volunteer users. You would need to raise a feature request at the link below:

Photoshop Family Customer Community

Dave

Omar.Fathy

Community Expert

You mean that you made an alpha channel for your image and saved it but when you open it again it is opened as PNG with transparency ?!

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