Photo: JPEG is recompressed when editing metadata only

[Paul Coddington]

Affinity Photo recompresses JPEG images when metadata is edited even though the image itself has no changes.

Steps:

1. Make a copy of a test JPEG image as backup.

2. Edit metadata in one copy of the image in Affinity Photo.

3. Stack before and after images in layers and view as Difference.

 

[loukash]

I think that's to be expected. APh is no metadata editor by definition.

[walt.farrell]

9 minutes ago, loukash said:

I think that's to be expected. APh is no metadata editor by definition.

But it could be improved to recognize that only the metadata has been changed, and to not affect the image data in that case 

[Alfred]

9 minutes ago, walt.farrell said:

But it could be improved to recognize that only the metadata has been changed, and to not affect the image data in that case 

Agreed. IrfanView does this if, for example, you merely change the Rotation metadata.

[Paul Coddington]

1 hour ago, loukash said:

I think that's to be expected. APh is no metadata editor by definition.

My perspective is that any application that has a metadata editing feature is, in effect, a metadata editor and expected to conform to the established standards of metadata editing.

Recompressing an otherwise unaltered JPEG is unexpected behaviour because the standards are designed to avoid that.

Turns out I got around the immediate problem using EXIFTool GUI, but it is much slower and more cumbersome to correct metadata that way (open another app, then browse down through a tree of folders, rather than just drag and drop from the currently open Explorer project working folder into an already open AFPhoto).

[walt.farrell]

9 hours ago, Paul Coddington said:

but it is much slower and more cumbersome to correct metadata that way (open another app, then browse down through a tree of folders, rather than just drag and drop from the currently open Explorer project

In the meantime, you could improve that by setting up File Explorer so you can use "Open with" or "Send to" to directly send a file to EXIFTool GUI, or ise another EXIF editor (such as Irfanview, mentioned earlier) that may allow that directly.

[Bit Disappointed]

Thus, I find myself returned to the hallowed halls of the university: "Define 'definition'."

There is no definition of what Photo is, but in practice, it's a budget-friendly editor very much "inspired" by Photoshop with its own strengths and weaknesses. Here, Photo should align itself with Photoshop, as it's not uncommon for a professional photographer to quickly edit an image in Photoshop. It's not always a batch task as some might think, and I even have an action set up for this, so I just need to enter the description and title, and the rest regarding copyright is inserted correctly. I often have to ship just ONE image in a hurry.

Since Photo's ancient algorithms for saving in JPG aren't very good, it's doubly important to avoid the scenario of recompression.

Quote

 

When you only change the metadata in a file in Adobe Photoshop CC and save the file, the actual data of the image typically does not get recompiled or recompressed if you do not make changes to the image itself. This means that the quality and compression of the image do not change merely by altering metadata such as description, tags, copyright information, etc.

However, it's important to pay attention to the save settings when you save the file after changing metadata. Photoshop offers different formats and settings for the saving process, and some of these can affect the file's compression. For example, if you save a JPEG file, Photoshop often asks about quality settings, which can change the level of compression. If you just make sure to keep the original settings and do not change the quality or format options, the file should not be recompressed based on changes in metadata alone.

At the very least, protection against unwanted recompression would be an excellent safeguard against accidents for customers using Photo. I, for one, do not.

[loukash]

10 hours ago, Paul Coddington said:

My perspective is that any application that has a metadata editing feature is, in effect, a metadata editor and expected to conform to the established standards of metadata editing.

In the mythical "perfect world", yes.

In the real world, however, e.g. even Apple has totally messed this up, as we have noticed just recently upon my bug report to the PixlPath developer: https://pixlpath.com/blog.html#2024_03_05

From my (limited) experience with a few cross-platform apps, XnViewMP is pretty good at writing metadata losslessly. It can be even configured not to change the modification date while doing so.

[Alfred]

20 minutes ago, Bit Disappointed said:

At the very least, protection against unwanted recompression would be an excellent safeguard against accidents for customers using Photo. I, for one, do not.

You do not what?

[GripsholmLion]

[walt.farrell]

37 minutes ago, Alfred said:

You do not what?

"Use Photo," presumably.

[fde101]

One thing to remember is that Photo *never* actually opens a JPEG.  It always works with its own custom document format.

When you "open" / import a JPEG image, it is being placed on a layer in an Affinity document.

When you "save" / "export" the document, you are exporting the Affinity document, not just the JPEG image.  Even if the image itself was not touched, you are not exporting the original JPEG, but the Affinity document which just happens to match its appearance.

Consequently, you are not "recompressing" the JPEG, but newly compressing the Affinity document which did not previously exist.

[Alfred]

24 minutes ago, walt.farrell said:

"Use Photo," presumably.

Duh, thanks! If instead of “customers using Photo” it had been worded as “customers who use Photo” then “I, for one, do not” would have immediately made sense to me.

[Pšenda]

21 hours ago, Paul Coddington said:

using EXIFTool GUI, but it is much slower and more cumbersome to correct metadata that way

I encourage you to explore the capabilities of this application - it is a unique tool for bulk metadata editing.