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Our final format is JPEG, which is great for archiving continuous tone digital photographs. Now it does have its limitations. Under no circumstances can you save layers or transparency, and JPEG always applies lossy compression, meaning that it rewrites the colors of the pixels as it saves the file. In return it delivers much smaller images. So for example, the layered version of this 45 million pixel panorama, saved to the native PSD format with maximized compatibility turned off, consumes 180 megabytes on disk.
That's pretty good given that as we can see down here in the lower left corner of the window, the image consumes 237 megabytes in RAM. When I save the flat version of the image to the TIFF and PNG formats using their lossless compression schemes, the image consumes about 70 megabytes on disk, which is less than half the size of the layered image. Using JPEG, we can get this file down to at most about 30 megabytes, which is half again the file size, and if we ramp up the compression like crazy we can get it down to 1 megabyte.
Let me show you what that looks like. I'll go up to the File menu and I'll choose the Save As command and then I'll go ahead and switch over to TIFF again for a moment so I can lift the file name by clicking on the existing TIFF file, then I'll switch from TIFF to JPEG. Notice that Photoshop turns off and dims the Layers check box and turns on As a Copy. I'll go ahead and click the Save button in order to bring up the JPEG Options dialog box. And I want you to understand how JPEG works so I'm going to go ahead and zoom in on the statue of Augustus Caesar right here in the center of the image.
And notice that right now for me the quality is set to the Maximum, which is 12, but I'm going to crank it down all the way to 0 so that we can see the JPEG compression do its thing. So the Preview check box is on, notice that we get to see what the file size will be which is about 1.3 megabytes. So this guy is going to be way smaller as a result, but of course it looks terrible. What's happening is that Photoshop is boiling down the image into 8x8 pixel squares. It tries to maintain the color of the top left square and then it bases all the other colors on that square.
So it looks rotten when zoomed in but check this out, as we zoom away from the file those squares end up reconciling and they don't look all that bad. Now you would never use a quality setting of 0, that's just too low. But I do want to give you a sense of how JPEG functions, and I want you to understand that that compression really does serve a purpose, and it very keenly exploits the way that our eyes read images. Problem is of course we would never be able to edit this file in the future. It would be dead to us.
It would just be a backup that we could send out to somebody else, what have you. What I tend to do with JPEG when I'm archiving images as opposed to creating web graphics, which we'll examine in a future chapter. I go ahead and crank the quality setting all the way up to 12. I never use anything but 12 these days. And you'll see that that still gives me a 27 megabyte image a little larger than a-third of the size of the TIFF and PNG files. Next you want to set your Format Options to Baseline Optimized, that just goes ahead and applies a little bit of additional lossless compression, and then click on the OK button in order to save off that image.
And now, just so that we can see it, we'll go ahead and press Ctrl+O or Command+O on the Mac to bring up the Open dialog box. I'll find that Antique theatre.jpg file and I'll click on the Open button in order to bring it up in Photoshop. And then I'll zoom in by pressing Ctrl+1 or Command+1 on the Mac, and I'll zoom in even further here, and you can see even when we're zoomed very far in, those squares that I was showing you before at the low quality setting are invisible here at the high quality setting, even though the file opens from 27 megabytes on disk to 130 megabytes in RAM.
And that is the power of archiving flat versions of your digital photographs to JPEG.
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