[Fixed] "Save for web" does not preserve resolution info (PPI aka DPI in case of scan/print image)

[porg]

Source image is a TIFF at 600 DPI from my scanner.
In this case preserving resolution matters because that scanned document shall get sent to a translator who should be able to print this true to scale.

Reproduction
1) Open in GraphicConverter (v12.0.1 build 6046) → File → Save for web…
2) Option "Reduce to 72 ppi" I left OFF.
3) I tried both with and without EXIF
No matter what: Saving that way looses the resolution info. I consider that a bug which should be fixed.

GraphicConverter 12 Save for web does not store PPI.png (63.76 KiB) Viewed 418 times

Why it's worth fixing: In contrast to the available workaround (see below) the "Save for web" dialog gives you an instant visual preview of the chosen quality and sharpness. So it would be cool if that special dialog also preserved PPI resolution.

Workaround 1: You still have the original lossless image (e.g. TIFF)

1) Open parent folder in GraphicConverter Browser and select it.
2) Use quick convert to JPEG: Embed JFIF or EXIF.
Both create a JPEG with the resolution preserved.

Workaround 2: You only have the lossy image (e.g. JPEG)
• which is de facto your 600 PPI version (still has all the pixels of your scan @ 600 DPI)
• Only the resolution metadata falsely is 72 PPI, e.g. resulted from the "Save for web" bug
• No worry, there's a solution for this too:
How to change resolution metadata of a lossy image format like JPEG without recompression

[forum_adm]

The issue is fixed in build 6121.

[porg]

Cool! Will update when the build gets available. And then test and report.

[porg]

Tested in b6121:

All JPEG and PNG export variants correct.
But WEBP with "Reduce to 72 PPI" OFF does not have an entirely correct outcome yet.
No downscaling occurred
Original resolution metadata LOST — AFAIK this should be possible with GraphicConverter, b/c some months ago with my involvement, we made sure that WEBPs can safe their Resolution in the EXIF junk within the WEB data stream.

GraphicConverter 12 b6122 Save for Web resolution metadata not preserved for WEBP.png (134.81 KiB) Viewed 403 times

Test file:

w150-babyblue-original-@2x.png (4.63 KiB) Viewed 403 times

And please: When your try to fix this: Try all 6 export variants (JPEG, PNG, WEBP with "Reduce to 72 PPI" once OFF and once ON) yourself before publishing. I would love to avoid a long round of ping pong testing for this particular bug.

[forum_adm]

Build 6123 will automatically activate the WebP option to always create an Exif record. So, the resolution can be stored.

[porg]

I propose it should be that way:

1) If the user decisively ticks "Include EXIF" ON, then that forces a creation of a Resolution tag within the EXIF to be able to preserve the resolution.

a) if the source image HAS a resolution tag. Then that's an exact preservation.

b) if the source image HAS NO resolution tag, than adding one, and inserting the default PPI (72 or 96 I guess) is unjustified. The most exact preservation of an absent value is to keep that value absent, not to set it to its default.

2) If "Include EXIF" is OFF (either by user decision or still the unchanged factory default) then no EXIF shall be added just to make the Resolution preservation possible. That would be quite intransparent (checkbox would contradict the outcome).

I strongly guess you implemented it that way. But please confirm that this is really the case.

[forum_adm]

Yes, the Exif tags will be added only if embed Exif is active.

[porg]

1) Glad that we agreed on the rulesets.

2) Tested in GC 12 b6123:
WEBP preserved its resolution from the PNG original, when "Save for web…" ran with "Embed EXIF" on , "Reduce to 72 PPI" off.

3) Detected a followup bug:
Browser column falsely shows resolution for WEBP files as 72 DPI regardless of real resolution

[porg]

Changed title to [Reopened] until investigated/fixed.

Tested again in GC v12 b6138, during testing related:
Browser column falsely shows resolution for WEBP files as 72 DPI regardless of real resolution)
and detected this regressing bug:

1) Opening a 144 PPI PNG

2) Save for web:

a) As WEBP + Embed Exif ON + Reduce to 72 PPI ON + (Lossless || Quality 80)
→ All results in 72 PPI WEBP.

b) As WEBP + Embed Exif ON + Reduce to 72 PPI OFF + (Lossless || Quality 80) + (Sharpen None || Sharpen 20%)
→ All results in 72 PPI WEBP.
Note: Once the same options plus the combo Lossless + Sharpen resulted in a 600 PPI WEBP. When this happened the save dialog contained the proposed filename "webp.webp" instead of "current-filename.webp". But I could not reproduce this later.

[forum_adm]

Thanks for checking.

But that is not a new bug. The implementation did not catch all cases. That should be fixed with build 6141.