I have directories containing many PDF files all with transparent backgrounds.
I normally view these thumbnails at a size of 300 and this is the perfectly acceptable result:
However if I reduce the thumbnails size to 250 this happens:
If I go back to 300 or above, all is OK.
Any ideas?
Is the same true in File Explorer?
Obviously in Explorer I can only use small and medium views and the transparency is not as obvious as I can make it in Opus, but, that said, at whatever size I view in Explorer, I get the PDF thumbs on a white background.
Which PDF software are you using to generate the thumbnails?
I build all my thumbnails with Mystic Thumbs to get the transparency
Can you upload an example PDF? I tried creating a transparent one in Photoshop but Mystic Thumbs renders it with a solid background.
Western Airlines Logo.zip (125.8 KB)
Making PDFs with transparent backgrounds is something of a black art in Photoshop. Transparency was not supporting, I understand until Acrobat 5 (PDF 1.4).
You can only get transparent backgrounds in Photoshop if you use the (High Quality Print Setting).
Mystic Thumbs seems to deal OK with creating transparent thumbs created in Photoshop with these settings.
Thanks for that. Unfortunately I can't reproduce the issue - it seems to work fine at any size. E.g. 128px:
Thanks for taking a look, Jon. Certainly here the PDF I sent turns black at 128. Perhaps I should start taking a look at my configuration.
Are there any points I should be looking for regarding Alpha channels, you can think of?
Is thumbnail caching on or off?
Thumbnail caching is on. Incidentally I have now found that the black background appears on thumbnail sizes below 256 pixels.
I have also found a reference to a problem some people had with Windows 7 and Photoshop CS where the PDFs had colour profiles attached, but removing the colour profiles from the Photoshop files and re-saving them does not seem to help.
But, hey, it is not the world's worst problem. I will just plug away at it in spare moments and let you know If I discover what it is.
It would be useful to know what the relationship between the Opus thumbnail cache and the Windows thumbnail cache is. For instance, are they one and the same thing? Do I have to clear the Windows and the Opus caches to clear thubnail cache completely?
Because transparency is a crucial issue for me I build my thumbnails with MysticThumbs. It is quick and effective even though you can only use one thumbnail thread in Opus.
My problem is this:
This screen shot was taken with the thumbnail size set in Opus at 257. As you can see, the transparency of the PDF files is displayed perfectly.
This is what happens if I set the thumbnail size to 256 or below:
The transparency has been lost.
Obviously the solution is to set the thumb size to 257, so it is not the worst problem in the world, but there are times when it is useful to set it to say 100 to get an overview of a directory that contains a lot of PDFs
Better to continue in your existing thread about this. I've moved the posts here.
Try turning off thumbnail caching to see if that is involved.
I suspect this issue is outside of Opus, however. The Windows shell's own thumbnail caching/scaling has/had some bugs where the alpha channel is trashed in some situations (including in Explorer), so this may be that.
I suspect you are right Leo. There is no transparency in Explorer. All transparent PDFs have the black background with you use medium of large icon in Explorer. This begs the question: Are these PDF icons being stored in Windows own icon cache, even though I use the Opus one? Just what is the relationship between the Windows icon cache and the Opus icon cache.
Thanks for your help. It is an annoyance rather than a big problem, so not worth wasting any more time over.
It's possible the shell extension is not setting the alpha channel correctly (e.g. not using premultiplied alpha, which is easy to miss), or it might be a bug in the shell. But if it's not working in Explorer either then it's not going to be something on our side of things.
Opus only caches thumbnails it generates itself. Ones that come via the shell are left to the shell to cache.
I am happy to say I have fixed this annoying glitch. It apparently affects thumbs creating in Mystic Thumbs prior to 4.4.2 and is associated with the way the earlier versions of the program dealt with transparency.
I have been trying to cure the problem by rebuilding the thumbs in the latest version of Mystic Thumbs within DOpus. This does not work.
However, if you go into Explorer and refresh the thumbs, you can watch as all the thumbs with black backgrounds are deleted and rebuilt with transparent backgrounds.
Now in Opus I can set the thumb size to whatever I want and the PDF thumbs have transparent backgrounds.
Thanks Leo for putting me onto the solution with your explanation of how thumbnail cache works.