Most photos are taken at a very large size and resolution, so they can be used for a variety of purposes. Every time you add an image to your PowerPoint document, the full size of the graphic is added to your file size. For example, if you insert a 2 Megabyte picture, your PowerPoint document grows by 2 Megabytes. If you have a lot of graphics, your file size can become unwieldy. It can make PowerPoint slow down or even crash and it can make it impossible to email your file. Compressing your images allows you to specify the quality of the graphic so that you can discard extra pixels keeping your file size as small as possible. In addition, if you have videos embedded in your presentation, if you trim the beginning or end, you can use the compress tools to delete the extraneous footage. Trimming videos is covered in detail in the PowerPoint 2010 Audio Video In-Depth course.
Let's take a look at this file, 07_06_compress in Windows Explorer. Here I can see that it's almost 142,000 Kilobytes or 138 Megabytes. That's pretty large. Certainly, too large to easily transfer to another computer over the Internet, and it may make your PowerPoint very, very slow. So let's compress our images. Now note, if you are planning to apply artistic effects to your images, compress your pictures first so that you don't reduce the quality of your special effects. I'll start by clicking on one of my photographs. Do note that compressing doesn't work on shapes or some clipart.
On the Picture Tools ribbon that appears I'll click on the Format tab. On the left-hand side, click on Compress Pictures. Now let's take a look at this dialog box. Apply only to this picture will just compress the one picture that I'm clicked on. We want to compress all the photographs in the slide deck. So I'm going to uncheck this checkmark. Delete cropped areas of pictures will completely remove areas of an image that you've cropped. This is a great way to remove large areas of the picture completely, but do note that you won't be able to reset your picture later.
Target output determines how much compression PowerPoint will apply. Choose according to your final purpose. PPI means Pixels Per Inch. Now a printer can print more dots than you can actually see on your screen. So the document will be printed, click on Print (220 ppi). Otherwise, your graphics will be fuzzy. Screen (150 ppi) is perfect for documents that will be viewed on a computer or projected, but not for printers. Email (96 ppi) will create the smallest file. Large files can't be emailed to some email addresses. So under 2 Megabytes is always safe. Use document resolution will default to the target output specified in PowerPoint's options and we'll take a look at those later on.
Now let me go ahead and choose Screen and then click OK. PowerPoint will think about it for a minute and now your pictures are compressed. So next, let's look at compressing your video and audio files. This will delete extraneous image and sound data and remove the beginning or endings of media that you've cropped and trimmed. This does result in lower quality images and videos, so only perform these steps if your file really is too large. First, let's save a copy of our presentation so that we can always go back to the original. This will give us two copies of the file; a high-resolution version to play on our own computer, and a smaller version for sharing. Since we're going to do our Save As now, our 07_06_compress file will still maintain all of our pictures that we just compressed in their original state. So I'm going to go to File and do a Save As and I'm going to add _compressed at the end.
Next, go to the File tab and take a look at Info. Under Media Size and Performance, we can see information about our movie. I can see that the movie that we have on slide 10 is 20 Megabytes and it does contain some trimmed regions. So I'm going to click on the Compress Media button. It gives me three levels of compression just like we saw with the images; Presentation Quality, Internet Quality, and Low Quality. For this presentation I'll choose Internet Quality. It's a medium level of compression and this choice is great if your playback is going to happen at a smaller size instead of full-screen.
After I click my quality, a Compress Media dialog box opens and I can actually watch as each asset is compressed. I can see the green progress bar at the bottom and when it done I'll see the final result for how much file size I saved. Sometimes the savings will be insignificant, but some media clips make it significantly smaller. So check this out. I saved almost 10 Megabytes. This can definitely help me squeeze my file onto the flash drive, save upload time, and avoid maximum file size constraints. I'll click Close. Notice that my Info screen now has some additional information.
It tells about my compression, and if I click on the Compress Media button, it also gives me an option for undoing the compression. That will take me back to my original resolution. Now here's one troubleshooting tip. If you get a message that one of the videos is unsupported, check its dimension. To take advantage of compression, both the width and the height need to be divisible by 4. If your movie has been resized, adjust it again so that both the dimensions can be divided by 4 and you should be fine. Now let me go back Home and let's go check out slide 10. This is the one that has my video on it. Let me go ahead and play a few seconds of the video.
(Jim Sugar: Later I got involved with some friends of mine at the Geographic,) (mostly Rick Orr who was a great science writer at that point.) I can see that the image is a little bit grainy, but it's subtle enough that I don't really mind. Let's save our file again and then go check out Windows Explorer. Whereas my original file was 138 Megabytes, my new file is only 10.2 Megabytes. That's a huge savings at only a small sacrifice of quality. Now let's go take a look at the default settings for compression. Go up to the File tab and down to Options. Click on Advanced, and over here look at Image Size and Quality. Compression defaults are applied to just this one document. Discard editing data will automatically delete all the information about your original image and you won't be able to use the Reset button to start over again. For example, PowerPoint will permanently forget its original size, color, and cropping. To remove any formatting you had applied you'd have to delete the image and reinsert it.
The next two settings, Do not compress images in file and Set default target output work together. While this is checked off, all the images will be inserted into the file in their original dimensions. If I uncheck it, I can set the target output to either the print quality, screen quality, or email quality. That way every time I insert a picture, it will automatically compress to 150 ppi. Well, let me go ahead and click Cancel on this window. Compressing your images is a necessary step when you have a lot of images or you want to email your file. But do remember to save a copy first in case the quality degradation is more than you're willing to sacrifice.
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