Converting png to jpeg increases image size

Question

When I convert png to jpeg , size of image is increasing for 2 percent cases. I am using convert command of imagemagick for this. Also able to handle alpha transparency factor by maintaing white background . But , I am not getting increase in size of image . It is very well known that pngs are lossless and jpegs are lossy , then what is the specific reason and what can be work around for it.

Please refer above mentioned example pic

Answer 1

Try decreasing JPEG quality setting. Jpeg uses Discreet Cosine Transform (DCT) to decrease the size of spatial data, but on high quality setting with high-detailed input images you will get some size increase due to the fact, that data is not quantized enough and DCT-ed data needs some storage too.