How to adjust thumbnail resolution and quality
The preferred way of changing the thumbnail resolution and quality is by changing the appropriate values in the TranscodePresetDocument in a shape tag.
To adjust resolution;
<thumbnailResolution>
<width>1200</width>
<height>800</height>
</thumbnailResolution>
To adjust quality;
<setting>
<key>thumbnailcompression</key>
<value>75</value>
</setting>
Where the value 75 is default and lower value gives you a more reduced quality.
NOTE: Quality adjustment is only supported for images.
More information on Thumbnails;
http://apidoc.vidispine.com/latest/ref/item/thumbnail.html?highlight=thumbnail