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Participating Frequently
May 21, 2022
Question

Save image as PNG with 32 bit

  • May 21, 2022
  • 4 replies
  • 15686 views

I can't save 32 bit PNG images. Here are the methods I've used...

1) No Alpha channel + Save As / PNG => 24 bit
2) Alpha Channel + Save As / *** No PNG option ***
3) No Alpha channel + Quick Export as PNG => 24 bit
4) Alpha channel + Quick Export as PNG => 24 bit
5) Alpha channel + Export As / PNG with Transparancy => 24 bit
6) Alpha channel + Export As / PNG without Transparency => 24 bit
7) No Alpha channel + Export As / PNG with Transparency => 24 bit

4 replies

Participant
February 19, 2025

I Googled this and found this link so for the benefit of anyone else having an issue. Im using Photoshop 26 and my pipeline was complaining that png's needed to be 32-bit and if you look at the properties of the file it does indeed show that it is 24-bit. So I thought I'd load it into PS and resave it. Various attempts would always save it as 24-bit. Then I found simply unlocking 'Background' layer to make it 'Layer 0' it would then save as 32-bit.

Stephen Marsh
Community Expert
Community Expert
February 20, 2025

@terrykingphotography 

 

Thank you for sharing your findings.

Stephen Marsh
Community Expert
Community Expert
May 22, 2022

My take is that a PNG file does actually have an alpha channel used for transparency, and then Photoshop will apply that channel to the file and remove it when the image is opened.

 

Here is a link to the PNG specification, specifically the section on colour and transparency:

https://www.w3.org/TR/2003/REC-PNG-20031110/#6Colour-values

 

Here is a sample image from a Wikipedia page:

https://en.wikipedia.org/wiki/File:PNG_transparency_demonstration_1.png 

 

When I run ExifTool on this image, I get this:

 

[PNG] ColorType: RGB with Alpha

 

This follows the PNG specification listing in table 6.1 - PNG image types and colour types linked above:

 

Truecolour with alpha

 

This is what Apple Preview indicates, there is a boolean value of 1 under "Has Alpha" which does not exist for a flattened PNG without transparency:

 

And this is what ImageJ reports for both the original and the one saved/exported from Photoshop - 32 Bit RGB (24+8):

 

However, when opened into Photoshop, there are only the primary RGB channels, there is no alpha channel – but there is transparency already applied.

 

When re-saving/re-exporting the original file from Photoshop with transparency, both ExifTool, Apple Preview and ImageJ all indicate that the image has an alpha channel. Of course, we can't verify this in Photoshop as it appears to apply and strip the transparency alpha.

 

I'll try to update these findings with some other software when I have time, perhaps one will show the intact transparency A channel and not just the RGB with transparency applied.

 

In some ways, this topic reminds me of the one on EXR alpha/transparency:

https://community.adobe.com/t5/photoshop-ecosystem-discussions/change-in-exr-open-from-cs2-to-cs3-can-this-be-fixed/m-p/1520950

 

EDIT: GIMP does recognise the Alpha channel for transparency, from both the original file and the one saved/exported from Photoshop.

 

Participating Frequently
May 21, 2022

That search gives a lot of answers that aren't relevant and the ones I'm reading that directly address the issue are in fact wrong! Photoshop will not save in 32 bit (4 channels) even when I take measures to do so.

Participating Frequently
May 21, 2022

For example one person suggests ...

If you save a PNG with the transparency option it MUST be using alpha. There's no other way to do it for 8-bit per channel. Does it work?
A) There is no answer, but I will anser it here, no, it does not work.

In another thread it is state 'Since "Quick Export As..." always saves PNGs as 32 bit,'
A) And that is plainly wrong!

c.pfaffenbichler
Community Expert
Community Expert
May 21, 2022

What do you mean? 32bit per Channel or 32bit overall? 

Participating Frequently
May 21, 2022

Either really. But probably 8bpc is what I'm focusing on now, although I do eventually need to know how to produce HDR images. Though I'm not sure yet if PNG can be used for such images.

c.pfaffenbichler
Community Expert
Community Expert
May 21, 2022

You may want to use tif or psd/psb for 32bit per channel images. 

 

As for an »8bit per channel plus transparency«-image: How does a PNG-24 creted via Save for Web fall short of your requirements?