Join Rufus Deuchler for an in-depth discussion in this video Image export options, part of Creating Ebooks with InDesign CS5.
The next panel we need to look at is the Images Option here. Images that are included in your ePub are very similar to the ones you view daily while browsing the web. The file formats are even the same, JPEG and JIF. Optimizing images for ePub is very important to keep the ePub file as small as possible and to also to reduce the computing power the eBook reader needs to display them. When creating layouts in InDesign, you typically use high resolution images for print, 300 dpi or more. Well, that resolution, of course, is far too high for an eBook. So InDesign, let's you automatically create optimized versions of your images. So, that they will display well in the eBook reader. If you select formatting here InDesign will preserve a formatting such as rotation or scale as much as possible for the images in the ePub. In this case, if this is selected the exported images are reformatted or down sampled to the size to which you have scaled them in your InDesign document. And you really have no control over how the resampling is done, what method is being used to resample your images or graphics.
And this can lead to unexpected results or even image degradation, also be aware that all images will be converted to the RGB color mode. That's a good reason, also to work in the RGB color mode from the beginning. Remember, from the very beginning, when we created the document, we told end design that the intention was web so the transparency module is already set to RGB. And also all images have their resolution down sampled to 72 dpi to reduce the file size in the generate ePub file. If you choose not to select formatted, any formatting applied to your images will be discarded.
The images however will still be converted to RGB color mode except grey scale images, and their resolution will be change to 72 dpi, if it is not already. This is why in our e book here we've imported the images already optimized. They were optimized using photo shop or fireworks from Photoshop I use the save for web feature, which allows me to make very, very small JPEGs. And then I used those JPEGs to be laid out inside of my InDesign document.
As far as image conversion here goes, this lets you choose whether the images in your document are converted to GIF or JPEG, or you can even choose automatic. InDesign will then decide automatically, which formats to use in each instance and it will do that for you. But as with all things automatic, there is really no way of knowing how and why inDesign makes its choices and what file limited color palette, that cannot exceed 256 colors.
So this is the best choice for maybe logos or simple graphics images that have, like flat colors, all right? The JPEG option, on the other hand, is the format that is best for images and illustrations with blends or gradients. So if your document combines both types of images, choose Automatic. Otherwise, choose the Compression Method that best fits your content. In our case here, what we have is a series of images that are already in the JPEG format. So, what I'm going to tell InDesign to do is to simply choose JPEG as the export option.
But let's quickly move back and also check out the automatic version here. Because there are some things that you can choose in the two different parts of that window. First, in the JIF Options, well you can choose between Adaptive, Web, System Colors, and System Colors for Macintosh. Basically, what these are Its a way of reducing the color palette available in the GIF, adoptive here the no dither creates a palette using a representative sample of colors in the image without any dithering, or added noise to the image to stimulate a larger spectrum of color, adoptive is actually your best choice for GIF optimization out of InDesign. The Web Option, on the other hand, creates a palette of 216 web safe colors. I'd say that this option has almost become obsolete, because most devices are capable of viewing color images.
That are far more superior to 256 colors, which was really the limit for 8-bit graphic cards. And the same thing goes for the system colors, Windows or Mac, which creates a palette using the built in operating system palette of 256 colors, some of which defer between Windows and Mac. As with the web colors up here, this options has become obsolete, as it is no longer necessary to optimize colors for various operating systems. If you choose interlace here, this lets you determine how your GIF will be rendered in the viewing device. If it is checked, and this option actually, slightly increases the file size of the GIF, the interlace option here, lets you determine how your GIF will be rendered in the viewing device.
Interlace GIF load one line at a time, gradually increasing the resolution of the image until it is fully loaded. Since the gypsy will be producing for you, ePub are not loaded on a web page and are serve locally within the ePub file, there is really no sense in selecting this option. Also because if this option is checked, the file size increases slightly. Let's look at the JPEG options here. Of course, we can choose the image quality, and we can from a very low quality, to a maximum quality.
After running some tests, at various image quality settings, I noticed that the quality itself is hardly affected, but the image size is impacted dramatically. For example, a JPEG exported as it's maximum quality results in to be 238 kilobyte and the same file size exported with low quality was 45 kilobyte that is more than 80% better compression. So, to choose the JPEG compression that fits your particular photos, just run different tests on the quality and on the compression ratios. And then decide what compression and image deterioration level you can live with inside of your ePub, all right? So, image quality you choose from here. As far as the formatting method of JPEG goes, it's quite similar to the JIF, a progressive creates images that increase in detail as they are downloaded. And baseline creates images that display only after they have been completely downloaded.
But again, since the images are bundled within the ePub, and that they are delivered directly on the reading device the best choice is just to use the baseline formatting method, okay? This is the one, not progressive. Progressive will also in this case make the file size slightly larger, all right? So in this panel here, we have everything we need to actually decide the compression of the images inside of our ePub. So in our case, we will leave it on JPEG dithering out the JIF options here and leave the image quality on medium. Because I have quite some detail in the images, they are all black and white etchings.
I need a higher quality, like the medium one and the format method we will leave baseline.
- Creating a new InDesign document with EPUB in mind
- Working with text
- Creating hyperlinks and cross-references
- Working with graphics
- Defining the reading order of the EPUB
- Other essential parts of an ebook
- Exporting to EPUB
- Customizing an EPUB