Btukfyl

Short answer: https://wiki.lyx.org/LyX/FiguresInLyX

Long answer:

To view a image on the LyX screen, it is required a compatible format with that XForms or Qt GUI libraries, namely bmp, gif, jpeg, pbm, pgm, ppm, tif, xbm or mng, png and xpm, respectively.

A message "Error converting to loadable format" mean that is not possible convert the image to PNG or any of these formats.

then you'll need to augment the list of known converters.

The link shows a detailed example of adding a converter. Pay attention that the converters are in the right path.

However,

If you see the "Error converting to loadable format" message only with
PDF files and you've verified that you have the converter tools
mentioned above, check which version of GhostScript you are using.

Version 8.7 of GhostScript has a known bug that prevents LyX from loading PDFs. Use the newest version. (The link above also explain a manual fix).

I'm using Lyx 2.2 under macOS Sierra. In my case, the problem was the ImageMagick version (7), and its incompatibility issues with LyX conversion scripts, as mentioned here: https://www.mail-archive.com/lyx-devel@lists.lyx.org/msg194142.html.

I'm using brew, so I fixed this problem by removing imagemagic and installing the latest 6.x version: imagemagick@6 and then creating a symbolic link (in /usr/local/bin) pointing to /usr/local/Cellar/imagemagick@6/6.9.7-5/bin/convert .

brew uninstall imagemagick

brew install imagemagick@6

ln -s /usr/local/Cellar/imagemagick@6/6.9.7-9/bin/convert /usr/local/bin/convert

Hope it helps

I'm using LyX 2.2.2 on Windows 7, and I have the same problem. After installing GhostScript 9.20, open LyX and click "Tools" -> "Reconfigure", finally restart LyX, and the problem is solved. I can see all PDF figures displayed in LyX. (However, the quality of the display is a little rough)

Ok rather than fiddling around with ImageMagick and Ghostscript, we can rely on sips which is built in to OSX. It's what the official fix does.

1. Go to Lyx->Preferences->File Handling->Converters.


2. Change the From format: to PDF (graphics), the To format: to PNG and paste this in the Converter: box: sips --resampleWidth 800 --setProperty format png $$i --out $$o.


3. Click Add. Yes this dialog is weird - you don't add an entry then configure it, you change the options and then click Add. Confusing.


4. Click Save. DO NOT CLICK APPLY! For some reason it shows an empty window and crashes Lyx.

The resulting PDFs can be a bit low res. You can increase the 800 if you like.

This fix should already be in Lyx 2.2.4 or later I think.

For me on OSX the problem was that I didn't have ImageMagick installed at all. I'm not sure when it was expected to be installed, but anyway. Just follow Hector's instructions:

brew install imagemagick@6

ln -s /usr/local/Cellar/imagemagick@6/6.9.7-9/bin/convert /usr/local/bin/convert

I had exactly the same problem for LyX 2.2, whereas previously LyX 2.1 worked fine. So what I did was moving the ghostscript folder and the imagemagick folder from LyX 2.1 to LyX 2.2, and it turned out that it is imagemagick that has something wrong.

Windows usernames containing certain non-alphanumeric characters like umlauts can cause the described symptoms.

On my system (Windows 8.1, LyX 2.2.2, ghostscript 9.15) Windows accounts with umlauts in their usernames suffer the problem described by Veridian: Embedded PDF images are not displayed in LyX, stating "Error converting to loadable format", even though they are displayed in the final PDF.
On the contrary, Windows accounts with alphanumeric usernames do not suffer this problem on my system.
This also holds for newly created accounts.

For me the following workaround helped:

• In LyX go to Tools > Preferences > Paths
  


• Set Temporary Directory to C:UsersPublicAppDataLocalTemp
  


• Make sure the path exists


• Restart LyX

For me, on Windos 10 the following solved the problem:

• Install Ghostscript (https://www.ghostscript.com/)


• Delete the "ghostscript" folder inside the LyX directory

In /etc/ImageMagick-6/policy.xml, comment out the lines like

<policy domain="coder" rights="none" pattern="(...)" />

This introduces a slight security risk, which may be (it seems!) ignored on a desktop system.

There is a non-obvious detail that can cause this error despite having setup a suitable converter.

So for example, following Fran's answer and the LyX wiki instructions:

https://wiki.lyx.org/LyX/FiguresInLyX

you decide to add a pdf to png converter. Since png is well supported and is among the GUI displayable formats, that is a reasonable choice.

Under linux you might decide to use:

pdftoppm -png -singlefile $$i $$o

which generates slightly smaller files than pdftocairo -png .... The difficulty is, the output file will be named outfile.png.png and LyX will be unable to find it, causing the error:

Error converting to loadable format

which leaves no real clue about what the problem is.

An easy way to fix this is to use the command:

pdftoppm -png -singlefile $$i > $$o

which generates outfile.png and LyX proceeds normally.

Another issue is the display resolution. Under the LyX options tab you may wish to set the display size to 75% or so - this does not affect the ultimate pdf size, but it makes it easier to see what you have inserted in the GUI, since you can see the whole image.