How To Edit Images In Preview On a Mac

Hi, this is Gary with MacMost.com. Today let me show you all the things that you can do in the Preview app to edit photos. 

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So the Preview app on your Mac actually is two apps in one. One is a PDF viewer and the other is an image viewer. Both of these can be used to markup and in some ways edit those types of files. Let's focus on Image Files. If you have an image file like this and double click it chances are it's going to open up in Preview unless you change the default app for those kind of images. But you could always just run the Preview app and open any image from there. Now you get the image here in a viewer and certainly you could use Preview just for viewing the image. As a matter of fact you can use the Plus and Minus buttons here to zoom in. You can use your trackpad to move around and just have it as an image viewer. 

But there are also some things you could do to edit the image. Now you'll find these under Tools and also by clicking here which is the Markup tool that gives you access to buttons here that do a lot of these functions. Let's just use the menu for now and use two items here. Adjust Color and Adjust Size. Adjust color brings up these controls for adjusting the colors and exposure in the image. Now there are not as many controls here as you'll find in the Photos app or in a regular image editing app but you do have some things like, for instance, exposure, contrast, highlight shadows, color saturation, temperature, and others here. You could also use the controls at the top here to change the levels and an Auto-levels button. There's a Reset All button. So if you have to do some basic changes to the colors or exposure in the image you can do it in Preview. 

You could also go to Adjust Size. This allows you to resize the image. So you can change it here to have it fit into a certain size with pixels and you can change the measurement type here. Pixels is what you probably want in most cases. So here it shows you the exact pixel size of this image and you could change it. For instance you can shrink it to only 2000 pixels wide. You can see the width and height match to keep the image looking the same. But if I were to turn off Scale Proportionally then I could actually scale it where it would compress or expand the image vertically but not horizontally or vice versa. Switching to percent is another way to adjust the image. So, for instance, I can go to 50% width which would be 50% height so that's a quarter of the size. You can also go to one of these measurements here and use it that way. Then you're working with the resolution here. In this case it's 72 pixels per inch so you have to take that into account when you're adjusting the width and height. You could also turn off Resample Image. In that case when you make a change here you would actually be changing the resolution. So the number of pixels would be the same but you would have a different resolution which means it would be a different default size when you brought it into other apps like word processing or page layout apps.

Not typically something you need to worry about since you could simply resize it in those apps.

But the main thing you would use this for is if the image is too big and you really want it to be smaller. So you can say change the width to only 800 pixels wide, 600 high. You could see it's a much smaller size now. It may be easier for you to upload to a website or to send it to somebody.

Now you can also Crop an image. Even without the markup tools turned on. You can see I've got crosshairs here as a cursor and I could click and drag to select an area. Once I've selected an area I could grab any corner or any side and readjust. If I click outside the area and drag I'm selecting a new area. But if I click inside I can actually move the area around. Note that when you go to select an area, if you hold Shift down you're going to get a perfect square. Once you've selected an area then you can go to Tools and Crop. That won't be active until you actually have an area selected. Then you can Crop to just that size. All things in Preview you can Undo. So I'm going to use Command Z to Undo and get back what I cropped out. 

There are also a few other things you can do without going to Markup Tools. You've got this Rotate button here. You've also got under Tools the ability to flip horizontal or vertical. Now you can go to Markup tools and do even more. The first tool here is a selection tool. That's set to be a rectangle which is what we've been using all along. But you could change it to something like an ellipse. Now I can select an elliptical area. Holding the Shift key down would give me a perfect circle. So I can select this area. Now what can I do with it. Well, if I go to Crop with something that's not a rectangle it's going to make some of this transparent.  JPEG images can't have a transparent area. But PNG images can. So when you go to Crop it's going to ask to convert to a PNG.   So you agree to that and you could see now converting to a PNG in this area out here will be transparent. If you don't want gray as the background color, that indicates it's transparent, you can go to Preview Preferences and go to General and you could change the window background color. So I could change it to something that maybe easier to see that is transparent. 

Now you could also go to Lasso selection which allows you to click and draw any shape that you want. When you finish it just automatically connects the beginning and end. So you could draw like this, release, and it connects the beginning and end there. 

Now with any of the selection tools there are other things you can do as well. Once you have this selection there I can click and drag the selection around to reposition it. But I could also Cut, Copy, or Delete. If I were to Delete it removes the section. It has to convert it to a PNG to do that so now that's transparent. If I were to Copy then I could Paste and now I have a copy of that area. I can move it around to wherever I want. I could grab a corner and resize it. I can even rotate it using two fingers on a trackpad. I could place it where I want. Using Cut would be the same as doing both a Copy and a Delete. So then after it's deleted now you can Paste it and put it somewhere else. 

Another thing you could do is you could select an area and then Copy and then go to File, New From Clipboard. This creates a new Preview document that just has that area that you selected. 

You also have the ability to use something called Smart Lasso which instead of a hardline is going to give you this red vague area and you could use that to try to outline an object or subject in the photo and it will try its best to make it fit the border of that object or subject. 

Now it's not nearly as good as using the equivalent tool in pro apps like Pixelmator Pro, Affinity Photo, or PhotoShop. Another problem with the Smart Lasso tool, and in fact with any of these tools, is you can only do one selection. In most other apps you could then hold down a key like the shift key and add to the selection, add another area or enlarge the selection in some spot. But in Preview it only allows you to do one selection and then anything else you do is going to remove that selection and do another selection.

Now there's also this Instant Alpha tool here. You click that and then you click in an area and then drag and it will try to select similar colors nearby. As you can see here you can grab part of the sky but eventually it starts to grab part of the rocks. So my selection there isn't going to be as good and I can't enlarge it by clicking in another area. It's just going to select that one area. But if you are lucky enough to get a nice clean area that's a solid color you can then have that selection here and hit Delete and it will make that area transparent. Or you can Copy and Paste it. 

Now most of the rest here has to do with pure markup. So you can Draw or Sketch. With Sketch I can draw something like this and then I get to choose either an approximation of what I just drew or the exact thing. Whichever one I do it's going to be this object I can move around resize. I can also use the tools over here to select the thickness of the line, the type of line, and I could even change the color right there. So then you get these kind of modifier tools here. Using Draw it draws much more specific lines and you can't really adjust it afterwards. But you can move it around and you can change the color. But you can't change the thickness of the line or anything like that. The shapes can do a variety of things. You can do lines. You can do some basic shapes like squares, circles, stars, and things like that. Each one has its own little special thing. Like, for instance, the star here has these green dots and I can drag one of the green dots to change the number of points. I can drag another green dot to change the depth of the points as well. I can move that around. I can change the line and line color. For the shapes that have a possible fill you can go here and actually fill them with a color. One interesting thing you can do is you can draw a shape like this. It remembers the last line of fill you used. But you can also go in and click Show Colors and then change the opacity. So I can have this kind of blue filter on top of things. Let's get rid of the line completely by setting the color to nothing. Now I've just got this blue filter. I can drag it to fill the entire photo here. So now I've got this color here. Click there, Show Colors, and you could see which color it is. I could change the color. Change the opacity. This gives you a much more variety of effects than just using the regular color adjustments we looked at before. 

You also have some cool tools here. Like this magnifier tool that we can adjust the size and the magnification. Then you have the Text tool here which allows you to put text. You could change the text here. You can click off of it and then drag it. It's a little tricky because if you have it selected where you actually edited text it's hard to get back into drag mode. Let's click off and then click onto drag again. For text you want to use this button here for modifying it including the color, font, and other things. With it selected you can use the trackpad with two fingers on it to rotate the text as well. Now note that all of these different markup things, like let's put a square here. Let's draw something. These are all things you could select and move around. But once you Save, I'll just do Command S to save, and then reopen the file they are now permanent. So you can't change these anymore. So the different layers you've got only work when you have the document open. As soon as you Save it they're permanent. However, Preview does allow versioning. So you can go to File, go to Revert To, and then say Browse All Versions. I've got this saved in iCloud. So if I go back a version and it's going to ask me to load from iCloud that version. You could see here, here's the version before I put these things on, when I just had a color on top of it. I go back again here and here's a version before I added all of that. I can do Restore. 

You can do Signatures here on an image although we usually associate those with PDF's. You also can access the color adjustment tools and cropping tools from the Markup Toolbar here. Finally, we have the ability to Export. So after you've made changes to it you could go to File, and then Export, and then you have a variety of Export options. So this allows you to use Preview as a way to convert image files. So I could go and choose a format. So you've got the better HDIC format but not as compatible. You can set the quality here and you could see it would give you a smaller file size. You could go with traditional JPEG and set the quality as well. Smaller file size and better quality. You also have a Share button here at the top which allows you to send this image directly from here to a Mail message or Messages. Airdrop it. Add it to Notes or add this to Photos. So maybe you've done some adjustments and now you want to add it to your Photo Library. You can do that.  

So editing Preview differs a lot from editing in Photos. Photos gives you better photography editing tools. There are many more ways to edit colors and exposure and things like that in Photos. But Preview allows you to do things like make parts of the image transparent. Select parts of an image, Cut them out and use them in other photos. So if you really want to know how to manipulate photos on your Mac with the native tools that come with it, it's important to learn both how to use the editing tools in Photos and how to use the editing tools in Preview.