There is a problem concerns the size of picture block and the quality of picture in the block.
When the size of block with picture is smaller then 30 mm (approx. 110 pixels), the quality of picture which contain lines of 1 pixel thickness, is deteriorated.
As a result of image resizing, the bulk of pixels of thin lines disappears, and the when size of block becomes smaller - the most part of pixels is lost.
I had tried to find solutions for this problem but none of several found methods of image quality improvement does gave some significant result.
Therefore there is a suggestion
1) introduce restriction on minimal size of image block, so they couldn't be resized lesser than certain square
2) reproduce sample images with smaller sizes (minimal size of image block)
This case samples would be only stretched or increased, therefore it shouldn't be a loss of quality
