If you are consistently saving your JPEG images at 100%/level 12 then simply by reducing that to 80%/level 10 will get you the same result for free. Given the above the only way it seems that you might be able to significantly reduce file sizes without adversely affecting quality using the JPEG standard is if you are starting with an uncompressed format, or that you have started with a maximum quality JPEG that has virtually no compression. Under these quality levels the file size is only marginally reduced, but with a rapid decrease in image quality. Above these levels there is no perceptible increase in quality, while the file size grows rapidly. It would seem that from published testing* that this "ideal" level of JPEG compression is achieved in Adobe products at 80% in Lightroom, and at 10 out of 12 for Photoshop. Also that the there is no detectable visual improvement between this compression level and that of a maximum quality JPEG file. I am aware that there would seem to be an optimum level of compression for JPEG files, where the difference between an uncompressed file (saved say as a TIFF) and the compressed file is virtually undetectable. Either way you are adversely going to affect the quality of the image, from the level it is already at. For the life of me I do not understand how they can do this, if you reduce the file size then you either have had to reduce the resolution of the image, or you have had to increase the compression ratio and discard more information from the image. They seem to be claiming that they have the ability, while still conforming to the JPEG standards to be able to reduce file size by 80% without affecting the quality of the image at all. I followed the link in the OP and really wonder how they can work this trick.
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