Thumbnails should keep their image format

[Traumflug]

Currently, all thumbnails created by the image api create JPEGs, no matter what the original picture type is. This is counterproductive, e.g. transparency and sharpness of PNGs are lost.

For a discussion regarding this, see
http://forums.reprap.org/read.php?33,254970,255152#msg-255152

A patch fixing the issue for the 'convert' method is surprisingly simple, it actually removes code:

--- image.php.2013-10-15    2013-10-13 18:58:17.000000000 -0700
+++ image.php   2013-10-15 04:21:32.000000000 -0700
@@ -298,7 +298,9 @@
         $cmd = escapeshellcmd($convert) . ' ' .
                '- ' .
                '-thumbnail ' . $img['new_w'] .'x'. $img['new_h'] . ' ' .
-               '-write jpeg:- ' .
+               // Keep the image format.  --Traumflug 2013-10-15
+               //'-write jpeg:- ' .
+               '-write - ' .
                // Using '--' produces "permission denied for file --".
                // Actually, convert (tries to) write two files, then,
                // one to stdout and one to $PWD/--. To avoid this,
@@ -336,7 +338,8 @@

             if ($exit == 0) {
                 $img['image']    = $scaled;
-                $img['new_mime'] = 'image/jpeg';
+                // We keep the image type now.  --Traumflug 2013-10-15
+                //$img['new_mime'] = 'image/jpeg';
                 $img['method']   = 'convert';

                 return $img;

The code surrounding the patch might not fit the standard code, because we need a workaround for a 'convert' bug. Nevertheless I think the idea of the patch is visible and easy to apply manually.

Further simplification might be a good idea, like the entire removal of the 'new_mime' variable. I can't see a point in changing mime types.

[oricgn]

I think instead of keeping the image format it would be better to generate always a png thumbnail.

[oricgn]

Fixed in master and phorum_5_2.