In D2123, the package ImageMagick7 could have been used, but igal2 package still depends of ImageMagick 6.
As igal2 only uses ImageMagick to create thumbnails, without any alpha / colorspace manipulation, it should work with ImageMagick 7.
Command analysis
The following commands are used at commit 26e31b7efc4 in igal2 Perl script:
| Line | ImageMagick 6 command | ImageMagick 7 command | Status |
| 367 | convert $opt_con -scale x$opt_y \"$fullfile\" \"$fullthumb\" | ||
| 371 | identify -ping -format \"\%wx\%h %b\" \"$fullfile\" | ||
| 379 | convert $opt_con -scale $dimension \"$fullfile\" \"$fullthumb\" | ||
| 404 | identify -ping -format \"\%wx\%h %b\" \"$fullfile\" | ||
| 430 | convert $opt_con -scale x$opt_bigy \"$fullfile\" \"$fullslide\" | ||
| 446 | identify -ping -format \"\%wx\%h %b\" \"$fullslide\" | ||
| 636 | identify -ping -format \"\%wx\%h %b\" \"$opt_d\/$opt_dest.$itile\" | ||
| 638 | mogrify -scale x$opt_t $opt_d/$opt_dest.$itile | ||
| 721 | identify -ping -format \"\%wx\%h\" \"$opt_d/$thumb\" | ||
-ping allows to "efficiently determine image characteristics" (command line options).
