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Batch Image Conversion with macOS Preview

Batch Image Conversion with macOS Preview
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Every now and then I find myself in need of converting an image to another format, especially when the application I’m working with does not support the file format I have at hand. Recently I find myself needing to convert several webp formatted files, a format developed by Google as a replacement for PNG, JPEG and GIF. Unfortunately quite a few applications still do not support this new(er) format.

There are a bunch of tools out there that can do this for us, like Pixillion from NCH Software (free version available), or online services like CloudConvert. MacOS however already comes equipped with a suitable tool that can help us with that – and can even handle a batch – called “macOS Preview“.

In this article:
How to convert images, to different file formats, with Preview that comes with macOS – one at a time, or in batch.




Converting to Supported File Formats

As mentioned above, we’d like to convert images to a different file format so we can work with the images in our applications that currently do not support the file format we have at hand.
I’ll illustrate this with “webp” images which I’d like to convert to JPEG or PNG, but basically this can be done with any format supported by the “Preview” application.

Please note that this will work for non-image file formats, like 3D models of MS Office documents, as well – however the result may not always be as great as one would hope for.

Short Version for the impatient … 

Open the file, or files, with the macOS Preview application.
When doing a batch: Select all file thumbnails on the right.
From the “File” menu select “Export” (or “Export Selected Images”), select desired file format and click “Save”.

That’s all there is to it …

Free Alternative – Webp Converter (offline) 

A free application called “Webp Converter”, which can be found in the Apple App Store (link), offers file conversion both ways between JPG/PNG and WEBP.
This application is available for Windows and MacOS – see Developer website, which also offers online conversion.

 

Preview Readable File Formats

These are the formats macOS Preview can read at the time of writing this article. Most of these we can read and therefor convert.
Note : I assume Apple will add support for other formats as new formats emerge and become more commonly used.

Preview Readable File formats
File Type Description Extension(s)
AI Adobe Illustrator artwork files (if PDF content included in file) AI
BMP Windows bitmap files BMP
CR2 Raw image file used by Canon cameras CR2
DAE Collada 3D files DAE
DNG Adobe Digital negative files DNG
DOC Microsoft Word Files DOC, DOCX
EPS Encapsulated PostScript files EPS
FAX Faxes (TIFF) FAX
FPX FlashPix files FPX
GIF Graphics Interchange Format files GIF
HDR High-dynamic-range image files HDR
HEIC High Efficiency Image File Format HEIC
ICNS Apple Icon Image files ICNS
ICO Windows icon files ICO
JPEG Joint Photographic Experts Group files JPG, JPEG
JPEG-2000 JPEG 2000 files JP2, JPG2
KTX KTX Software OpenGL/Vulkan Textures and images KTX
OBJ Wavefront 3D files OBJ
OpenEXR OpenEXR files EXR
PBM Netpbm Portable BitMap (black & white) PBM
PDF Portable Document Format version 1.5, with some additional features PDF
PGM Netpbm Portable GrayMap (gray scale) PGM
PICT QuickDraw image files PICT, PCT, PIC
PNG Portable Network Graphics files PNG
PNTG MacPaint Bitmap Graphic files PNTG
PPM Netpbm Portable PixMap (color) PPM
PPT PowerPoint files PPT, PPTX
PS Adobe PostScript files PS
PSD Adobe Photoshop files PSD
QTIF QuickTime image files QT, QTIF, MOV
RAD Radiance 3D Scene Description files RAD
RAW Raw image files RAW
SGI Silicon Graphics Image files SGI
STL STereoLithography 3D format files STL
TGA TARGA image files TGA, ICB, VDA, VST
TIFF Tagged Image File Format files TIF, TIFF
XBM X BitMap files XBM
XLS Microsoft Excel Files XLS, XLSX

Preview Writable File Formats

At this time, Preview can write the following formats from macOS Preview:

Preview Writable File formats
File Type Description Extension(s)
JPEG Joint Photographic Experts Group files JPG, JPEG
JPEG-2000 JPEG 2000 files JP2, JPG2
OpenEXR OpenEXR files EXR
PDF Portable Document Format PDF
PNG Portable Network Graphics files PNG
TIFF Tagged Image File Format files TIF, TIFF

Warning – Converting non-images, like documents (Word/Excel/etc) and 3D model files (STL, OBJ, etc) may not produce the best results.

Note – At the time of this writing, Preview does not yet support the much more efficient WebP format for export.

Convert one Image

To convert a file, we will first need to open it with Preview.
Obviously this can be done in several ways … these are you options:

  • Double click the file if Preview is already the default file viewer for this file format.
  • Right click the file, and select “Open With” – “Preview” in cases where Preview is not the default viewer.
  • Open Preview, and select the file (when Preview gets opened, a file dialog will appear).
  • With preview already open, chose from the menu “File” – “Open“.

 

Open file with Preview

Open file with Preview

Now that we can see the image or document, we convert it by using the Export functionality of macOS Preview.
This is done by opening the ‘File” menu and selecting the “Export” option.

Preview - Export File as ...

Preview – Export File as …

Next a file dialog will open:

Preview - Export File Dialog

Preview – Export File Dialog

Here we can enter the filename, and select one of the available formats:

Preview - Available Export Formats

Preview – Available Export Formats

 

And finally click “Save” …. and this is all there is to it.

Convert a Batch of Images

The same method as described for one image can be used for batch conversion – even with a mix of different source files.
For example, we can convert several different files, for example JPG, WEBP and TIFF mixed, all at once to say PNG files.

The steps are similar: Open all files that you’d like to convert in Preview.
You’ll see on the left-side of the opened image, a list of thumbnail:

Open multiple files with Preview

Open multiple files with Preview

Now select the first thumbnail by clicking it once with the left mouse button.

To select all files:
Scroll all the way down (either with the scroll wheel function of your mouse, or the slider on the right of the thumbnails), hold SHIFT and select the last thumbnail in the list.

Preview - Multiple files selected

Preview – Multiple files selected

The next step is the same as what we did with a single image: we will need to Export the files.
This is done again by opening the ‘File” menu and selecting the “Export Selected Images” option.

Preview - Export selected Files ...

Preview – Export selected images …

Next we will see a file dialog similar to what we have seen when converting a single file, with a few small difference though …

  • First of all we will need to click “Options” to get access to selecting a file “Format“.
  • The other thing is that we cannot enter a filename for our files – Preview will use the filenames of the original files for this (with a different extension of course).

Finally we click “Save“, and all files will now be saved in the selected format, in the selected directory.
And that is it … 😊

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