3.3 MB Pasted Image becomes 22 MB Message
TB 102.13.0 (64-bit)/macOS 13.3 (22E252)/2023 MBP, 16", M2 Max
If I take a photo on my iPhone 12 SE/iOS 16.5.1 and AirDrop it to my Mac, it's 3.3 MB:
https://www.kan.org/pictures/IMG_8281.HEIC
If I attach it to a message (as an attachment) in TB, the message size is about 4 MB.
If I copy/paste it into the message body, the message size balloons to ~22 MB. You can test this just by Saving the message to your Drafts folder; you don't have to actually send it.
Resizing the pasted photo within the message body doesn't affect the message size, as it appears to change the rendering without resampling.
The result is the same whether I copy on the iPhone and paste it into TB on my Mac, or whether I AirDrop it to my Mac, open in Preview, copy from Preview, and paste into TB.
Is there a way to resample the image within TB to reduce its file size without going through another app like Preview? Sometimes it's more instructive to have inline messages, exactly where they need to be in the body of my email, rather than having them as attachments. And copy/paste directly from my iPhone would be a great productivity enhancer if not for the size bloat.
Thanks!
Solution choisie
I don't have an iPhone, but a friend shared with .heic image files with me. So on Windows, I opened a 1.61 MB .heic file in Windows Paint (it seems to know how to decode them), selected the entire image and copy/pasted it into the body of a message. After sending, I checked the Sent folder and the message is 19.3 MB. Wow.
I use View > Message Source to open the source code of the message and (after a very long wait) found this information about how the image was encoded into the message body:
Content-Type: image/png; name="XRFk01tvNLMXbv6O.png" Content-Disposition: inline; filename="XRFk01tvNLMXbv6O.png"
As you probably know, PNG is a compression format that is best used for large areas of flat color and is very inefficient for most photos.
I repeated the experiment with a 4.3 MB JPEG file, and this time the message size showed as 17.7 MB and I see:
Content-Type: image/png; name="86xUeWNjlYFZZMU2.png" Content-Disposition: inline; filename="86xUeWNjlYFZZMU2.png"
So the issue is not exclusive to HEIC files.
After further research...
Thunderbird's Config Editor has a setting for the preferred image format for pasting (clipboard.paste_image_type). I'm not sure there is a single optimal setting for this because it depends on what you are pasting. However, I think it's worth experimenting with JPEG for your use case, even if it diminishes image quality to some extent. For further information:
If there is an easier way to toggle that, I couldn't tell you.
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Solution choisie
I don't have an iPhone, but a friend shared with .heic image files with me. So on Windows, I opened a 1.61 MB .heic file in Windows Paint (it seems to know how to decode them), selected the entire image and copy/pasted it into the body of a message. After sending, I checked the Sent folder and the message is 19.3 MB. Wow.
I use View > Message Source to open the source code of the message and (after a very long wait) found this information about how the image was encoded into the message body:
Content-Type: image/png; name="XRFk01tvNLMXbv6O.png" Content-Disposition: inline; filename="XRFk01tvNLMXbv6O.png"
As you probably know, PNG is a compression format that is best used for large areas of flat color and is very inefficient for most photos.
I repeated the experiment with a 4.3 MB JPEG file, and this time the message size showed as 17.7 MB and I see:
Content-Type: image/png; name="86xUeWNjlYFZZMU2.png" Content-Disposition: inline; filename="86xUeWNjlYFZZMU2.png"
So the issue is not exclusive to HEIC files.
After further research...
Thunderbird's Config Editor has a setting for the preferred image format for pasting (clipboard.paste_image_type). I'm not sure there is a single optimal setting for this because it depends on what you are pasting. However, I think it's worth experimenting with JPEG for your use case, even if it diminishes image quality to some extent. For further information:
If there is an easier way to toggle that, I couldn't tell you.
Brilliant! I've been searching for this for years.
My draft is now a very-reasonable 4.8 MB, with an inline image.
Thanks!