Sepia-toned images: Adjust the Sepia slider.Grayscale images: Drag the Saturation slider all the way to the left.The color tool comes with sliders to adjust various parameters such as exposure, contrast, and saturation. To bring up this tool, click on Tools > Adjust Color. If you want to, say, sharpen a photo or change its brightness or saturation, you can do so with Preview's light and color adjustment tool. Want to select irregularly shaped portions of a photo before editing? The rectangular marquee selection tool isn't much help for that.

If you want to crop out the area you selected and keep the rest instead, click on Edit > Invert Selection.

Once you're satisfied with the selection, click on Tools > Crop to crop the photo. Hold down the Option key if you'd like to scale the selected area up and down from the center. If you want to limit the selection to a perfect square, hold down the Shift key during selection. Want to move the marquee selection to a different part of the photo? Click and drag the selection to where you want it to show up. It's convenient that you can see the dimensions of the selected area at the edge of the cursor. The tool is active by default all you have to do is click and drag the mouse over the relevant area to select it. That's where the rectangular marquee selection tool comes in. To crop a photo, you'll first need to select the part of it you want to keep.

How to use mac preview to edit pictures