I just checked the standard code that generate thumbnails ("PreviewJob"):

"kdelibs/kio/kio/previewjob.cpp":

    if (bNeedCache)
    {
        if (width <= 128 && height <= 128) cacheWidth = cacheHeight = 128;
        else cacheWidth = cacheHeight = 256;
        thumbPath = thumbRoot + (cacheWidth == 128 ? "normal/" : "large/");
        KStandardDirs::makeDir(thumbPath, 0700);
    }

Also, the directory thumb creator has its cache method:

"kdebase/runtime/kioslave/thumbnail/thumbnail.cpp":

KMD5 md5(QFile::encodeName(fileName.url()));
        const QString thumbName = QFile::encodeName(md5.hexDigest()) + ".png";
        if (m_thumbBasePath.isEmpty()) {
            m_thumbBasePath = QDir::homePath() + "/.thumbnails/";
            KStandardDirs::makeDir(m_thumbBasePath + "normal/", 0700);
            KStandardDirs::makeDir(m_thumbBasePath + "large/", 0700);
        }

As you can see both standard methods honor the standard.
So, it is a different app (or a KDE app using a custom method) which could be causing this.

As a test you could:
- Clean your .thumbnails folder
- Start and use every app you normally use and check after every run if the thumbnails with unusual large are created in normal/

- What other graphics application are you using ?

Regards

Sorry, I didn't pasted the relevant code of "kdebase/runtime/kioslave/thumbnail/thumbnail.cpp":

        QString thumbPath = m_thumbBasePath;
        if ((segmentWidth <= 128) && (segmentHeight <= 128)) {
            cacheSize = 128;
            thumbPath += "normal/";
        } else {
            cacheSize = 256;
            thumbPath += "large/";
        }

Moving to "kde" until we determine which apps generate the thumbs in the wrong place.

Then it must be a problem specific to Dolphin. It's certainly the case that enabling Preview mode in Dolphin causes this. I just assumed Dolphin used standard thumbnail generator code, but I guess it doesn't. Feel free to reassign there.

Mh, Dolphin uses an interface to the PreviewJob code I showed to you in comment 1.

Did you tested removing the thumbs cache and browsing some folders with Dolphin that would show this issue ? 
Thanks

I'm trying to work out a way to reproduce this. I cleared out .thumbnails and set up a couple of basic 1600x1200 test images in a lone test folder. Now, I haven't managed to find a way that saves the full 1600x1200 image as a thumbnail yet, but I've discovered that if I use dolphin to browse .thumbnails/large, then fullsize copies of those large thumbnail images (with different hashes) will appear in .thumbnails/normal. The two problems with this behaviour, of course, are (1) the image size, and (2) it probably isn't wise to be generating thumbnails for files inside .thumbnails, anyway.

This is very odd considering preview.cpp line 245:
!(*kit).url().directory( KUrl::AppendTrailingSlash ).startsWith(thumbRoot)) &&

I think the problem is createSubThumbnail in thumbnail.cpp:
if (subCreator->create(filePath, cacheSize, cacheSize, thumbnail)) {
    // The thumbnail has been created successfully. Store the thumbnail
    // to the cache for future access.
    KTemporaryFile temp;
    temp.setPrefix(thumbPath + "kde-tmp-");
    temp.setSuffix(".png");
    temp.setAutoRemove(false);
    if (temp.open()) {
        tempFileName = temp.fileName();
        savedCorrectly = thumbnail.save(tempFileName, "PNG");
    }
} else {
    return false;
}

This creates a thumbnail for use as a sub-thumbnail for in the generation of folder thumbnails, but it performs no size checking on the image that's created by the sub-thumbnail generator.

ImageCreator::create seems to return the image without scaling. Presumably the assumption is that this is safe because the get method in thumbnail.cpp does this:
if (img.width() > m_width || img.height() > m_height) {
    double imgRatio = (double)img.height() / (double)img.width();
    if (imgRatio > (double)m_height / (double)m_width) {
        img = img.scaled( int(qMax((double)m_height / imgRatio, 1.0)), m_height, Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
    } else {
        img = img.scaled(m_width, int(qMax((double)m_width * imgRatio, 1.0)), Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
    }
}

createSubThumbnail doesn't do that.

If I'm correct, then this is how unscaled images work their way into the thumbnails folder.

Peace,
Brendon

SVN commit 1011482 by ppenz:

Assure that the thumbnails of directory previews don't exceed the cache size. Thanks to Brendon Higgins for the detailed analyses.

BUG: 203512
CCBUG: 202960

 M  +15 -8     thumbnail.cpp  
 M  +6 -0      thumbnail.h  


WebSVN link: http://websvn.kde.org/?view=rev&revision=1011482

SVN commit 1011483 by ppenz:

Backport of SVN commit 1011482: Assure that the thumbnails of directory previews don't exceed the cache size.
Thanks to Brendon Higgins for the detailed analyses.

BUG: 203512
CCBUG: 202960

 M  +15 -8     thumbnail.cpp  
 M  +6 -0      thumbnail.h  


WebSVN link: http://websvn.kde.org/?view=rev&revision=1011483