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Understanding web file formats

From: Illustrator for Web Design

Video: Understanding web file formats

When it comes to graphic file formats on the web, we have three basic choices that we need to be aware of and those are GIF, PNG, and JPEG. In this movie, we're going to be exploring the various web file formats that we can export out of Adobe Illustrator and when and why we should use each one. So I've got a document opened here and I'm just going to open the Save for Web dialog box. We're going to go into the Save for Web dialog box a little bit later in depth to explain all the options that I have available to me in here, but for now I just wanted to show you the options that I have in terms of file formatting.

Understanding web file formats

When it comes to graphic file formats on the web, we have three basic choices that we need to be aware of and those are GIF, PNG, and JPEG. In this movie, we're going to be exploring the various web file formats that we can export out of Adobe Illustrator and when and why we should use each one. So I've got a document opened here and I'm just going to open the Save for Web dialog box. We're going to go into the Save for Web dialog box a little bit later in depth to explain all the options that I have available to me in here, but for now I just wanted to show you the options that I have in terms of file formatting.

So we have JPEGs, GIFs, and PNGs available to us. I'm going to start with JPEG. And so JPEG is what we call a lossy file format, meaning that when we compress an item with JPEG compression, it does cause degradation and can cause pixelation. The lower quality you set for a JPEG image, the smaller the file size is going to be, but the worse the image is going to look. So for instance, if I happened to turn this down to a low quality, you could start to see some of that nastiness pixelation and chunky artifacts that start to appear. If you've ever done a Google image search, you've probably seen this countless number of times.

The JPEG file format is not good if you always want those good clean graphics, because depending on the compression level, you might not get such a nice result. However, it is the best when you're saving out photographs, because photographs need that large continuous-tone image to be displayed properly on the web, and JPEGs give you the best color gamut for that as well. When you're dealing with photographs on the web, you need to save those as JPEGs. Also if you have smaller graphics that can be optimized at a higher compression rate without losing that quality, you could save those out as JPEGs as well.

But one thing that JPEGs do not do is transparency. You notice here that the background of my graphic is completely white. That's called a matte, and the matte behind this graphic is being caused because I'm using the JPEG. Normally, this would just be transparent, and I could save this out and the logo could just float wherever it needed to go. But since I've chosen JPEG, no transparency whatsoever, so this would actually be a huge graphic in the long run. The next file format that we're going to talk about is GIF, and GIF is good for large areas of broad color and graphics that have really sharp, well-defined edges, without the need of complex transparency.

Now I know that's a lot to swallow, but just let me break it down in terms of this. If you have small icons or big square graphics with large bits of the same color, that's where you need to save a GIF. GIFs are not good for gradients. They are not good for objects that use multiple colors sort of close together. They're also not to be used with any graphics that require the use of complex, or what we call absolute, transparency, things like drop shadows, blurs, and things like that.

So in this case, it would actually work okay with this graphic, because there's no drop shadow. There is really clean defined edges around this robot, and there's only two or three colors being used, and they're in pretty large blocks all the way across. You do see some degradation around the logo right there in the middle, but all in all, a GIF would work okay for this graphic. The other graphic that we have available to us inside of Illustrator is something called a PNG file. And PNG files come in a variety of different flavors, actually: you have something called a PNG-8, a PNG-24, and something called a PNG-32.

When you look inside of the Preset dropdown you will not see an option for PNG-32, and I'll explain that in a minute. You do have the option for a PNG-8 and a PNG-24. The PNG-8 is essentially the same type of graphic as a GIF. It has the same rules and the same type of things applied to it. No complex transparency, large blocks of color, et cetera. PNG-8 is going to give you in most cases a smaller file size than a GIF, so you might want to consider that, as long as you don't have any complex transparency areas. The PNG-24, that is the Mac Daddy of all graphics when it comes to saving out for transparency, because of the fact that it supports something called true alpha transparency.

And the only difference between a PNG-24 and a PNG-32, which is not available inside of Illustrator, is the name. Think of a PNG in terms of bits. So you have 8 bits for the red channel, 8 bits for the green, 8 bits for the blue, and you also have 8 bits for the alpha channel. You add up all those to together, 8 times four, that's 32 bits. In Illustrator and other programs like Photoshop, they simply ignore that last eight bits for the alpha. They do include it. It's in there, but they just don't add it into the file format.

In an app like Adobe Fireworks you actually get a PNG-32, which actually accounts for that last bit of transparency. So if you're in Photoshop or Illustrator and you need something with super-complex transparency that uses drop shadows, blurs, or something like that or it's just a logo that really needs to be absolutely crisp and sharp, go with the PNG-24. If you're in a program like Fireworks, you could utilize the PNG-32 and it would work perfectly as well. So hopefully by now you have a better understanding of what these file formats are for and how they are used and why you should use each one in a given scenario.

My suggestion would be to go through and practice exporting out several graphics at different file formats, take a look at the difference between them, see which one suits your needs the best, and then commit that to memory so that each and every time you come into the Save for Web dialog box you can easily optimize your images accordingly, save them out, and save yourself a ton of time.

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This video is part of

Image for Illustrator for Web Design
Illustrator for Web Design

67 video lessons · 24783 viewers

Justin Seeley
Author

 
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  1. 1m 13s
    1. Welcome
      50s
    2. Using the exercise files
      23s
  2. 43m 51s
    1. Designing for screens
      1m 57s
    2. Decoding screen size and resolution
      2m 40s
    3. Exploring the Illustrator to HTML workflow
      3m 42s
    4. Setting up Illustrator for web work
      6m 55s
    5. Creating a new document for web
      6m 25s
    6. Creating a new document for mobile
      3m 31s
    7. Using artboards for responsive layouts
      7m 42s
    8. Creating email newsletter documents
      4m 31s
    9. Working with Pixel Preview and anti-aliasing
      6m 28s
  3. 25m 28s
    1. Adjusting color settings
      6m 47s
    2. Understanding web color
      3m 47s
    3. Creating a color palette
      5m 4s
    4. Creating custom swatches
      4m 50s
    5. Working with fills and strokes
      5m 0s
  4. 13m 15s
    1. Exploring the Layers panel
      5m 21s
    2. Renaming and grouping layers
      7m 54s
  5. 24m 5s
    1. Drawing simple shapes
      4m 16s
    2. Working with Pathfinder
      5m 4s
    3. Using the Shape Builder tool
      4m 33s
    4. Creating symbols
      6m 24s
    5. Editing and replacing symbols
      3m 48s
  6. 20m 22s
    1. Planning your project
      2m 56s
    2. Using guides and rulers
      5m 56s
    3. Developing a layout with shapes
      6m 21s
    4. Using a grid system
      5m 9s
  7. 25m 53s
    1. Exploring the rules of typography
      4m 1s
    2. Using text as text vs. using text as an image
      3m 37s
    3. Understanding web-safe fonts
      1m 46s
    4. Creating and using paragraph styles
      5m 16s
    5. Creating and using character styles
      3m 2s
    6. Simulating the CSS box model
      8m 11s
  8. 21m 17s
    1. Understanding object appearance
      4m 43s
    2. Applying and editing live effects
      3m 34s
    3. Creating and using drop shadows
      3m 13s
    4. Creating more flexible rounded rectangles
      3m 17s
    5. Saving appearance as graphic styles
      6m 30s
  9. 35m 57s
    1. Starting with a wireframe
      5m 23s
    2. Adding master elements
      6m 45s
    3. Creating navigation buttons
      13m 34s
    4. Working with photographs
      5m 50s
    5. Simulating pages with artboards
      4m 25s
  10. 54m 45s
    1. Creating video placeholders
      10m 33s
    2. Creating buttons
      13m 1s
    3. Creating form fields
      8m 15s
    4. Creating radio boxes and checkboxes
      5m 11s
    5. Creating progress bars
      10m 12s
    6. Creating tabbed interfaces
      7m 33s
  11. 35m 28s
    1. Understanding slicing
      3m 26s
    2. Slicing up a mockup
      3m 6s
    3. Understanding web file formats
      5m 33s
    4. Exploring the Save for Web dialog
      3m 50s
    5. Optimizing photographs
      4m 29s
    6. Optimizing transparent graphics
      4m 43s
    7. Saving Retina display graphics
      3m 46s
    8. Exporting SVG graphics
      6m 35s
  12. 9m 29s
    1. Understanding image sprites
      3m 4s
    2. Creating a sprite grid
      4m 36s
    3. Optimizing sprites for the web
      1m 49s
  13. 15m 29s
    1. Placing Illustrator Smart Objects
      3m 22s
    2. Sharing color swatches between apps
      2m 9s
    3. Exporting Illustrator artwork as a PSD
      3m 49s
    4. Importing artwork into Fireworks
      2m 41s
    5. Exporting HTML from Illustrator
      3m 28s
  14. 1m 19s
    1. Taking the next step
      1m 1s
    2. Goodbye
      18s

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