highest resolution for printing

karenjantz wrote: I want everything to be transferred in the highest resolution for printing. It goes from 4MB to 1.7MB

How are you transferring pictures out of Photos? Do these two files look different to you?

If you use File>Export Original, then you get exactly the same file that you put into Photos, the same size but no edits or captions that you might have added.

If you use File>Export nn Photos, then you get the edited version. You can choose the quality of the Photos in the dialog

If you choose JPEG, Maximum, and Large, then you will get a file that has the best quality. Larger files may not mean increased quality. TIFF, for instance, may provide a more precise copy, but it's a larger file that may not appear any different.

You asked specifically about resolution, and you referred to megabytes, but resolution is not the same as megabytes. Resolution is the number of pixels. A picture that is 4000 pixels across can be printed as a larger image than one that is 1000 pixels across. Your eye, maybe 10 inches away from a picture, can't see individual pixels if there are more than about 300 pixels per inch. So 4000 pixels printed to 13 inches would look smooth when held 10 inches away. If you look at the picture from farther away, say two feet, then you could print the picture 28 inches across or so, and it would look smooth.

Megabytes is about how much information is in the picture. A 4000x3000 pixel image, in color, can take up 36 megabytes. That's sort of like a RAW image. But if the picture is of the sky, all blue, then you don't need all of those megabytes to describe it and, if there are a few clouds, it might not take up even a megabyte, and it would still be exactly the same picture.

Image files are usually compressed. You can make a picture much smaller without losing any information at all, so-called lossless compression. JPEG, though, is a compression method that reduces the size of the file even more by preserving especially the information that the eye can see. It's very clever, and it's very, very difficult to tell that there's been any compression in a high quality JPEG file.

So, it may be that the 1.7 MB file is just a better compression than the 4 MB version-- sometimes the extra size is not extra useful information.

I always choose JPEG, Maximum, and Large, unless I want to send a smaller image in an email or text.

I'm not sure if this addresses your concerns. Let us know...

Resolution in printing is dependent on the number of pixels in the image and not on the file size. Read this: The Myth of DPI.

When you export the photo out of the Photos library export as an edited photo with the following settings:

JPEG Quality: Maximum

Size: Full size

The rest as you see fit:

If you want to preserve the original image file at its original quality use "File > Export > Export unmodified original" to save the file. Using "File > Export > Export ... Image" will always apply a format conversion and should only be used, if our image has adjustments applied and you want to save a copy of the edited version.

At the Apple article below, please check the section: Export photos in a selected format

Export photos, videos, slideshows, and memories in Photos on Mac - Apple Support (CA)