A .cbz is a zip of images with no manifest and no page order. The order is the filenames, and sorting those the way a computer does puts page 10 between page 1 and page 2. That single fault is what makes most converted comics unreadable.
Digits are read as numbers here, the resulting order is shown before you convert, and JPEG pages go into the PDF byte for byte.
There is not much to a comic archive, which is the appeal and the problem. Rename a .cbz to .zip and you can open it in any file manager: a folder of images, occasionally a ComicInfo.xml, and nothing else at all telling a reader what order to show them in.
What is actually in a .cbz
- Image files, one per pagethe whole document
- No manifest, no page listorder is the filenames
- ComicInfo.xml, sometimesmetadata, not a page
- Occasionally a cover thumbnailin a subfolder
Compare that with an EPUB, which carries a spine listing every document in reading order, and the difference is stark. A comic archive has no such thing. Every reader that opens one is guessing, and they guess differently.
Page 10 does not come after page 1
Sorting text puts "10" before "2", because it compares character by character and "1" is less than "2". That is correct for words and wrong for pages, and it is the reason a converted comic so often opens on its eleventh page.
The fix is to read runs of digits as numbers rather than characters, which puts 2 before 10 and keeps 01 alongside 1. It also has to work inside folder names, because a collection split into ch1, ch2 and ch10 has exactly the same problem one level up.
What happens to the pages
A PDF page can carry JPEG and Flate-compressed image data, and between them those cover almost every comic archive in existence. A JPEG page is copied in without being touched at all. A PNG page is decoded and re-compressed, which sounds worse than it is: Deflate is lossless, so the picture that comes out is the picture that went in, pixel for pixel.
JPEG goes in byte for byte, which is most scanned and most released material.
PNG is decoded and re-compressed with Deflate, which is lossless: identical picture, different bytes.
Either way the page in the PDF is the page in the archive.
Which is why the PDF comes out about the size of the .cbz.
WebP, AVIF, GIF and BMP, which a PDF page cannot carry.
Decoded and written back out as JPEG at high quality.
A visible but small loss, on formats that are rare in comics.
Every file it happens to is named in the result line.
Each page becomes a page the size of its own image rather than being fitted to A4. A comic page is the artwork, and putting it on a sheet would mean either margins around it or cropping it, neither of which anybody wants. If you do need a uniform sheet size, for printing or for binding with something else, Resize PDF does that afterwards and shows you what it costs.
The .cbr problem
CBZ and CBR look like the same format with two names and are not. The Z is a zip and the R is a RAR archive, and RAR is a proprietary format whose decoder is not something that ships in a browser tool. So a .cbr cannot be opened here, and saying so plainly is better than a vague failure.
The fix takes about ten seconds and belongs on your machine: open the .cbr in any archive tool that reads RAR, extract it, and re-zip the images as a .cbz. Nothing is lost, because the images inside are the same images.
When a PDF is the right container, and when it is not
- Reading on a device with no comic reader. This is the main reason people convert. Every phone, tablet and computer opens a PDF; not all of them open a .cbz.
- Sending it to somebody. A PDF arrives as a document rather than as an archive an email filter might strip.
- Printing or annotating. A PDF can be marked up, signed and printed with a page range. An archive cannot.
- Not for reading on a dedicated comic reader. If you have one, it already handles .cbz better than it handles PDF, with two-page spreads and panel-by-panel view that a PDF viewer does not offer.
Why this runs in your browser
Comic archives are large, often hundreds of megabytes, and uploading one to a converter means waiting twice over: once to send it and once to get it back. On a slow connection that is most of an afternoon for a job your machine can do in seconds.
The archive is opened in memory, the pages are embedded, the result is checked by reopening it with the same engine your browser uses, and it is handed back as a download. Nothing is transmitted.
The tool is right above
Reading order worked out and shown, pages kept as they are, nothing uploaded.
Common questions
Order, formats, and the archive type this cannot open.
01My pages came out in the wrong order. Why?
Almost always because the archive numbers its pages without padding, so 1, 2, 10 sorted as text puts page 10 second. This sorts runs of digits as numbers, so page 10 lands after page 9. The order is shown before you convert so you can check.
02Can it open a .cbr file?
No, and that is a format difference rather than a limitation. A .cbz is a zip and a .cbr is a RAR archive, which needs a different decoder that is not here. Any archive tool will re-save a .cbr as a .cbz in a few seconds.
03Does it re-compress my pages?
JPEG pages go in byte for byte, which is most comics. PNG pages are decoded and re-compressed with Deflate, which is lossless, so the picture is identical even though the bytes are not. WebP, AVIF, GIF and BMP have to be re-encoded as JPEG, which is the only lossy case, and the result line names the files it happened to.
04Why is the PDF about the size of the archive?
Because a CBZ is a zip of already-compressed images, and a PDF of it holds the same pictures with a thin wrapper. There is nothing left to squeeze. A PNG comic can move a little in either direction, since those pages are re-compressed rather than copied.
05What page size does it use?
Each page is the size of its own image. A comic page is the picture, so fitting it onto A4 would add margins nobody asked for and shrink the artwork. Use the resize tool afterwards if a uniform sheet size is what you need.
06What happens to ComicInfo.xml and the cover?
Anything that is not an image is skipped and listed, so a short page count always has a reason next to it. A cover stored as an image is kept as a page; where it lands depends on its filename.
07My pages are enormous scans. Can I cap them?
Yes. The longest-edge limit scales pages down as they go in, which is worth using for a 4000 pixel scan that is going to be read on a tablet.
08Are my files uploaded anywhere?
No. The archive is opened and the PDF built in your browser. Nothing leaves the device.