Save image as PNG with 32 bit

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.

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.

A common topic:

https://community.adobe.com/t5/forums/searchpage/tab/message?advanced=false&allow_punctuation=false&filter=location&location=category:ct-photoshop&q=32%20bit%20png

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