Bridge/Camera Raw: DPI displayed wrong for PNG

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  • Problem
  • Updated 4 months ago
  • Solved
  • (Edited)
Lately i find that in bridge PNG files show up having DPI of 72 while actually beeing 300 !

I know it looks futile, but i deliver to customers who care, using older software.

Created a new file inside PS setting 300dpi....confirmed by the IMAGE SIZE command ... saved as  JPG, PSD, and PNG ..

below the screencast showing the faulty PNG value.
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Gerard Van Den Elshout

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Posted 2 years ago

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Stephen Marsh

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This issue is deeper than one may at first suspect.

Photoshop Export/Quick Export strips the resolution metadata, as does Export/Save for Web (Legacy). Photoshop Save As will retain resolution metadata.

The official PNG specification for the PNG resolution unit is in metres (not inches).

So a 300 ppi save as PNG from Photoshop would embed a value of 11811 ppm (pixels per metre). When Photoshop opens a PNG with this resolution metadata, it performs a “translation” from pixels per metre to PPI:

118.11 x 2.54 = 299.9994 ppi, rounded up to 300 ppi.

If there is no resolution metadata embedded in the file, then Photoshop defaults to 72 ppi.

Of course, Bridge does not perform the same translation, so there is a discrepancy where Bridge indicates the resolution as 72 ppi when Photoshop does not. Later versions of Bridge simply show an arbitrary value of 72 ppi. Earlier versions of Bridge, such as CS6 showed no resolution information at all.

At one point in time, at least for CC2015, Photoshop was adding in extra metadata that was not to the PNG specification. The extended metadata was: 

[XMP-tiff] XResolution: 300

[XMP-tiff] YResolution: 300

[XMP-tiff] ResolutionUnit: inches 

And this “out of specification” metadata addition did allow Adobe Bridge to display a resolution entry the same as the Photoshop translation... However Adobe stopped doing this and now things are back to “normal” (whatever that is).

Should Bridge show no resolution metadata as it did in CS6, even if there was resolution metadata in the file?

Should Bridge be doing what it currently is, assigning an arbitrary 72 ppi value?

Should Bridge show the same “translated” resolution metadata as Photoshop?

Should Bridge show the resolution metadata as per the PNG specification in pixels per metre?

What should Bridge do if there is no resolution metadata in the file?

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Gerard Van Den Elshout

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VERY clear answer..thank you...!  
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Rikk Flohr, Official Rep

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Updates to Lightroom Classic, Camera Raw, and the Lightroom Ecosystem were released yesterday and contain a fix for this issue.  Please install the appropriate update and see if it solves this problem. You can read more about the updates here.

Thank you for your patience.