As for image size...how large (kb) are the jpg files for methane and ethane?
I took a screen shot of the image you had before, cropped it, and saved as an indexed png to get these (1.4kb and 1.3kb respectively). Even if you only save 2-3kb per image, I would imagine you will have a lot of images in that kind of book and that equates to a significant savings in file size. You would also probably get much better quality than I did because you are working with the originals.
