How To Batch Process Images With Mac Preview

If you need to change several image files at once, adjusting their sizes and maybe exporting in a new format, you can do it with Preview on your Mac.
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Video Transcript: Hi, this is Gary with MacMost.com. Today let me show you how to Batch Process images using Preview. 
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So let's say you want to change the size or the format of a group of image files. Doing this is called Batch Processing. Most Image apps, like PhotoShop, have this ability. However, you can also do it with a built-in Preview App on your Mac. 
Let's say I've got these images here. Now if I were to select one of these images and look at the information I could see it is 4032 pixels wide. It's a JPEG image. If I were to double click on it it would open up in Preview by default. Then I could go to Tools and I can adjust the size, and change the size. I could also go to File and then Export and then Export a new copy in a different format, perhaps reducing the file size considerably. 
But what if I wanted to do it for a whole bunch of files. I've got 5 here but maybe you have 50 or 500 images. You can use Preview to Batch Process all of these. So the first thing you want to do is select them all. You can use Shift Click to select them all on the List here. I'm just going to use Command A since I want every file that is in this folder. Now I'm going to open them. I could just double click on one since they are all selected they should all open in the default app, which is Preview, or I could use Command O which is File, Open. 
Then you'll see they open in Preview and what you're going to look for is a Sidebar that shows you all the images. So they open in one window, not in Tabs, this one window here with all the images listed on the left. Now if that doesn't happen it may be because of your Settings. For instance, if I go to Preview, Settings here and then go to Images you could see When Opening File, if I have it set to open each file in its own window, then opening all of these will open every single one in its own window and you can't use this technique. 
So you want to set it to Open Groups of Files in the Same Window or Open All Files in One Window. Now when you open them it should open one window with each of the images here on the left and you can switch which image you are looking at. Better still you can select more than one image. You can select one image and then Command Click to select another one, or you can select one image and Shift Click to select a range, or you can just use Command A and it selects them all. That's a keyboard shortcut for Edit, Select All. 
So now with all of these selected you could actually go in and change all of them at once. If I were to go to Tools and then Adjust Size you could see it gives me the size of all the images, in this case they are all the same. If not it would just give me the first one. Then I could set it to something else. So I'll change it to 3000 pixels wide. You could see here a summary. You could see it is going to change the size to 74.4% of the original and there are five images it is going to change. You can see here it is going to be 12.7 MB down from 17.7 MB.  Now if I click Okay you could see it is Done. I don't have to Save or anything. It's automatically saved. So I can Close this window here and now I can look at these files. If I select the first one you could see it is now 3000 pixels wide. 
Now you can do other things with the same technique as well. So I'll Open all of these again. Do Command A to select them all. Notice that if I go to Tools and then Rotate I can rotate all of them. I'm going to use Command Z to Undo that. Other tools will work as well such as the Flip tools here. But adjusting color won't work. If I go in here and I change, say, the exposure to make this darker you can see it just changes that one image. But will work is Exporting. So I have all these selected here and if I go to File, and then Export Selected Images then I can choose a location. I could also Show Options. So I can change the format. So let's use the newer HEIC format here. I can change the quality. It's going to give me an estimate here of the quality for one of the files. Let's put it right there in the middle. Then I will choose. Now it is going to export.
If I look in the Finder now I'll see my originals. I decided to Save these in the same location so now I see the new ones right next to it. You could see that it is the same dimensions but the better compression I'm getting with HEIC has made the files much smaller. 
So this is a great technique to use, say, if you wanted to share a bunch of images with somebody or upload them online. You can first reduce the dimensions and then export, maybe with higher compression levels and get smaller files. Do it with a whole batch of them at once. Now do note that when you change dimensions or when you rotate images it is going to automatically save these. So if you want to keep the originals you first want to duplicate all the images or duplicate the folder they are in and make the changes to new copies, leaving your originals untouched.
I hope you found this useful. Thanks for watching.
How To Batch Process Images With Mac Preview

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