The JPEG compression encoding process splits a given image into blocks of 8x8 pixels, working with these blocks in future lossy and lossless compressions. [source]

It is also mentioned that if the image is a multiple 1MCU block (defined as a Minimum Coded Unit, 'usually 16 pixels in both directions') that lossless alterations to a JPEG can be performed. [source]

I am working with product images and would like to know both if, and how much benefit can be derived from using multiples of 16 in my final image size (say, using an image with size 480px by 360px) vs. a non-multiple of 16 (such as 484x362). In this example I am not interested in further alterations, editing, or recompression of the final image.

To try to get closer to a specific answer where I know there must be largely generalities: Given a 480x360 image that is 64k and saved at maximum quality in Photoshop [example]:

• Can I expect any quality loss from an image that is 484x362
• What amount of file size addition can I expect (for this example, the additional space would be white pixels)
• Are there any other disadvantages to growing larger than the 8px grid?

I know it's arbitrary to use that specific example, but it would still be helpful (for me and potentially any others pondering an image size) to understand what level of compromise I'd be dealing with in breaking the non-8px grid.

The key issue here is a debate I've had is whether 8-pixel divisible images are higher quality than images that are not divisible by 8-pixels.