Pages EPUB export converts JPEGs with rounded corners to larger PNGs

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Pages EPUB export converts JPEGs with rounded corners to larger PNGs

Size increase in EPUB Document from Pages

There are many topics here discussing how the size of a Pages document increases greatly when exported as an EPUB file (or as a PDF). Sadly most (all?) of these are closed yet there is little hard explanation of what causes the problem. I created this topic to record one concrete reason.

My Pages document contains quite a lot of large (half-page and bigger) photos, inserted as JPEG files with the JPEG quality set quite low to reduce the file size. An exported PDF is rather smaller than the Pages file but the EPUB was twice as big. Some digging showed that the JPEG files in the Pages document had been exported as PNG files in the EPUB file with the PNG files being (understandably) much bigger than their JPEG equivalents.

The JPEGs in the Pages file all have slightly rounded corners (just from dragging the little green square at the top-left corner of their frame). The PNGs mimic this using transparent corners. I deduce that EPUB doesn't support any on-the-fly mechanism for masking the image shape so Pages retains the appearance with transparency by changing to PNGs (JPEG does not support transparency) - but they're much bigger.

Removing the tiny curved corners reduced my EPUB size by about a third, leaving it not too much bigger than the Pages file. I'm to criticising Pages here because it faithfully reproduced the document's style but the cost in file size is startling.

Hope this helps.

MacBook Pro (M1 Max, 2021)

Posted on Oct 6, 2026 2:26 PM

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Answer 1

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VikingOSX

Level 10

131,134 points

Oct 7, 2026 5:32 AM in response to Command_F

When you round the corner of an image in Pages you introduce transparency to the image's bounding box. There are no transparent JPG, so it must be converted to PNG on export to EPUB. The increase in PNG image size is accounting for those extra transparent pixels. The original image type and size is retained in the saved Pages document.

I just tested this with a 350K JPG that I applied a rounded rectangular shape in Pages. The resulting PNG image in the Fixed EPUB was 2.2 MB.

With the same original image and no rounding treatment, when exported to Fixed EPUB, it retains its original name, file type (JPG), and size (350K).

The moral here is get fancy with images in Pages (e.g. rounded corners, picture frames, drop shadows) and you will pay the price in the resulting EPUB export image conversion and bloat.

Tested: Pages v15.4, macOS 27.0.1

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Answer 2

VikingOSX

Level 10

131,134 points

Oct 7, 2026 9:26 AM in response to Command_F

So, if you want special appearances of images in Pages without that transparency-induced size increase, open that JPG in an external image editor of your choice and apply the radius corners to it there. Then export as PNG, and drop that in Pages. That same sized PNG will be in the exported EPUB.

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Answer 3

VikingOSX

Level 10

131,134 points

Oct 12, 2026 11:22 AM in response to Command_F

Open the JPEG image in an external image editor of your choice. Round the corners of the image per that application's procedure. Select that rounded image and export as PNG. Drop that PNG into Pages in place of your original JPEG and the PNG will not be converted or resized when the document is exported to EPUB.

I tested this in Pages v15.4 on macOS 27.0.1 using the free Affinity Studio v3.3.0. It can be done in the free GIMP tool, or any other. Mentioned the image sizes in my previous post.

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Answer 4

Command_F Author

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19 points

Oct 12, 2026 12:52 PM in response to VikingOSX

Drop that PNG into Pages in place of your original JPEG and the PNG will not be converted or resized when ... exported to EPUB

If you start with a PNG and export that then I don't doubt it. However, I was starting with photo JPEGs and had created them at relatively low quality. Converting them to a PNG, as Pages does or as I would have to do to start your scheme I've quoted above, gives me the size increase I'm trying to avoid. In a quick test with Preview, converting a 3840x2560pix photo JPEG at a file size of 1MB produces a PNG of 16.2MB.

Remember that JPEGs (of photos) use their lossy compression to very good effect. PNGs are not really designed for photos and similar and generally have only lossless compression (let alone a transparency overhead, even if it is "cheap") - it's not a fair fight!

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Answer 5

VikingOSX

Level 10

131,134 points

Oct 13, 2026 2:23 AM in response to Command_F

You can use unmodified JPEG images in Pages and their size will not change in the resulting saved Pages document, or EPUB export. As soon as you add transparency by using any image mask, or picture frame, the EPUB export process will convert it to PNG. You do have a choice in the matter, though there is no user override of EPUB conversion to PNG when it senses introduced image transparency.

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Answer 6

Command_F Author

Level 1

19 points

Oct 12, 2026 10:08 AM in response to VikingOSX

I thought you meant to apply the corners to the JPEG by colouring them white (or whatever) but you then say to export them as PNG. Did you mean export as JPEG again; if not, I don't see where the saving in size comes from?

The idea of editing the curved corner into the JPEG before Pages ever sees it seems a good one to me. The only snag is if you can't predict the background colour (or if it is patterned etc).

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Answer 7

Command_F Author

Level 1

19 points

Oct 7, 2026 8:59 AM in response to VikingOSX

Agreed. I saw similar dramatic size increases in the conversion from JPEG to PNG.

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