How do I get photoshop to crop where my selection (marching ants) is and not outside of it. I have feathered set to 0px.
Basically your claim/assumption sounds strange, at least I can not reproduce the issue and have not observed such happenings with Image > Crop.
if you switch to Quick Mask Mode is the Selection truly sharp?
Anyway, cropping does not seem to be necessary as Edit > Define Pattern can work based on an active Selection.
I was following a tutorial on making seamless tiles and the person used image > crop; so, I used it. I will try to make my selection and go directly to edit > pattern and see if it is better.
I am not sure what Quick Mask mode is; but, will look into it.
But, I do notice when I crop anything, my image gets cropped just outside of the crop box. It is not noticeable when zoomed out; but, when you zoom in you notice it. In regular images it is not important because it is so small. I will keep trying different settings to see if it still happens. But, if the "make selection and then Edit > Pattern works well, I will use it.
Could you please post screenshots?
The screenshot in my first post showed the cut. The marching ants were on the cyan guide.
I tried this again today, after Photoshop was shut down over night, and it actually cut along the guide where the edge of my selection was. Something must have messed up within Photoshop for it to do that.
If it happens again, I will post a screenshot.
I just did some tests and it is not the cropping, it is the rectangular Marguee Tool. I place my cursor on the intersections of the horizontal and vertical guide to start my rectangular selection. It does not start at the intersection even though under View > Snap To, I have it set to only snap to Guides. The selection starts at the bottom right corner of the image pixel, not my guide intersection. So really, the Snap to Guide is not very good if it still picks the bottom right corner of a pixel. I understand that images will be cut on the edge of pixels and will not cut a pixel in half or in quarters (unless there is a setting I do not know about).
The image I tried this on is patterned; so, I thought making a nice rectangular selection would make an easy seamless tile. It did not when you zoom in to look at it closely. Zoomed out it looked fine though.
So, I guess when making a seamless tile from a background image, it is best to use the Offset method of tile making instead of using only the crop image method. Otherwise, you will end up having very small gaps.