Hi @yuvrajb70925184
1. Top three renditions are thumbnails and thumbnails are always png(48:48, 140:100, 319:319)
2. There is one extra web renditons from AEM, which will be jpeg or png based on source image type.
Below is the workflow of dam renditions
http://localhost:4502/etc/workflow/models/dam/update_asset.html
thumbnail step: Process Thumbnails
Renditions step: Create Web Enabled Image --> You need to add this step from side kick, multiple times in workflow and give required renditions (Like 1280, 1680, 720 ......)
The other better solutions is use Dynamic Media in aem which does better job. By creating a Tiff(image-set) and can render any sizes at run time, with right params.
https://helpx.adobe.com/experience-manager/6-3/assets/using/config-dynamic.html
Then you can access renditions like
http://localhost.com:4502/is/image/content/dam/renditions/img-03.jpg?wid=960&fmt=jpeg&qlt=90,0&resMode=sharp&op_usm=1.1,0.5,1,0