Thumbnails for alpha channel (transparency) with checkerboard

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Apr 20, 2020, 10:12:18 AM4/20/20
to JPhotoTagger Users English
Dear fans of JPhotoTagger,

after a lot of testing of free and commercial DAM tools for photo and media file management I still like and use JPhotoTagger heavily.
I use it for really ALL kind of multimedia and other PC files, because JPT is a very flexible, user friendly and simple tool for DAM tasks.
I know a lot of experts, who dislike the philosophy of separate sidecar files (XMP), but I support an like this method in JPT very much.
All this is also the reason why I left MediaPro, Idimager, Lightroom, Xnview and even Imatch.
Meanwhile I use only DigiKam for photos, MusicBee for Music and JPhotoTagger (JPT) for all other media files.

A lot of windows tool rely on the limited features of OS Windows thumbnail generation
or thumbnail software like (Icaros, FastPictureViewerCodec, MediaPreview, MysticThumbs, SageThumbs, ...).
I like to report about the big benefit with JPT to create thumbnails with free external tools (convert, mplayer, dcraw, ...) and DOS batch files.
JPT is much better with this methods, because you can create the usual checkerboard background behind images with alpha channel to make the transparency visible.
This is escpecially good for black svg or png graphics with transparent background.
Very often these images show black thumbnails with black background (not really good).
Not so with JPT, when special commands with ImageMagick are used.

Here is one example for the thumbnail batch command for PNG files
%conv% %IMAGE% -thumbnail %MAX_DIM%x%MAX_DIM% -auto-orient ^ ( -size %wxh% tile:pattern:checkerboard -brightness-contrast 0,-50 ) ^ +swap -compose over -composite jpg:-
The variable %CONV% stands for "drive/path/convert.exe"
The varialbe %wxh% stands for the image dimensions which have to be calculated based on the original image aspect ratio and thumbnail size %MAX_DIM%.
Such calculation can be done with prior DOS batch commands "set /a ...".
On request I can provide more details.

For e.g. ICO files with multiple images inside, the batch file is a little bit more complicated.
In this case I am using the free tool "Quick-Any2Ico.exe" for exporting the largest PNG from the ICO file.
This PNG is then the base for thumbnail with transparency.

Best regards and thanks to Elmar

from James

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