Optimal PNG or JPEG image compression quality / low file size - PHP

What is an optimal PNG or JPEG image compression quality when using PHP imagepng() or imagejpeg() ? I need to get a good image quality, but also a low file size.

Hi,

Good quality for image compession is:

• PNG - around 5
• JPEG - around 75

These compressions levels should provide a good image quality and relatively low file size. I recommend to use at least some conversion to get images with low file size. Images with no compression have often large file size.