Join Gabriel Powell for an in-depth discussion in this video Optimizing graphics for the EPUB format, part of Creating Ebooks with InDesign CS4 or CS5.
If you're creating a e-book that contains images and graphic, it's important to prepare them for optimum display on a variety of different e-book readers. In this lesson, I'm going to give you several best practices to follow when laying out images in a document that will exported as an EPUB file. There's an abundance of e-book readers available on the market today. They come in a variety of different sizes. Some people read e-books on their mobile phone, others read them on a dedicated e-book reader, such as the Sony Reader, the Barnes and Noble NOOK, or the Amazon Kindle.
And others read e-books on the Apple iPad or even a regular computer. As you can imagine, it's not actually possible to predict which e-book readers people will read your e-books on. So, let me demonstrate some best practices to follow that will ensure that the images and graphics in your e-books will display well across a variety of different e-book readers. The first thing that I like to do is convert the measurement system to either pixels or points. With InDesign CS5, you can use the pixels measurement system to change the measurement system.
Simply position your pointer where the rulers, the horizontal and vertical rulers, converge, here, at the top left part of the document window, and then, right-click. And from this menu, choose Pixels. Now, if you're using InDesign CS4, the pixels measurement system isn't available, so instead you would use points. Either way, you get the same results. Since I'm working with InDesign CS5, I'll go ahead and select Pixels. So, by using either the points or pixels measurement system, you can more accurately predict the size of your images in an e-book. So, I'll go ahead and scale this image to a size that looks good on various e-book readers.
But, what size should an image be when there are so many e-book readers available? Well, you don't want to make the images and graphics too small, because they won't display well on large screen sizes. You also don't want to make them too large, because that will increase the size of your e-book file and large e-books don't perform well on reading devices with limited processing power. Fortunately, most dedicated e-book readers have a screen resolution of 600 by 800 pixels, so I recommend using that screen resolution as the basis for sizing your images. Let's take a look at the current dimensions of this image. I'll select it and take note of the width and height of the image up here in the Control Panel.
The average image should be between 300 pixels and 600 pixels wide and the height of the image should proportional to the width of the image. So this image will display well on most e-book readers. Now, an image that's 300 pixels wide will fill exactly half of the screen on most e-book readers. So, I'll go ahead and resize this image to 300 pixels wide. I'll first click this icon here, which will constrain the proportions when I resize the image, and now, I'll just type in 300 pixels here. And press Enter or Return to apply that.
And now, I'll fit this image to the frame. So, to do that, I'll go up to the Object menu, choose Fitting, and then Fit Content Proportionally. And now, I'll view this document at exactly 100%. Now, I can be sure that this image will appear at exactly these dimensions in the EPUB file. I'll go ahead and export an EPUB file, from the File menu, I'll choose Export For, and then EPUB. I'll send this to the Desktop.
I'd like to view this e-book after exporting it, so I'll click this option, and then, in the Images section of the dialogue box, I want to make sure and select the formatted option. With the formatted option selected, the exported images are reformatted to the size to which you've scaled them in your InDesign document. The images are also converted to the RGB color mode and their resolution is changed to 72 pixels per inch, which helps to reduce the overall file size of the final EPUB file.
This option also preserves any InDesign formatting that you've applied to your image frames, such as a stroke, a fill, any rotation, or even cropping that you've done. I'll go ahead and click Export. And, as you can see, this image is exactly the same size in the EPUB file as it is in my InDesign layout. So as you can see, it's really quite simple. Just make sure you're working in either the Pixels or Points measurement system.
Scale the image to the size that you want it to be in the eBook reader, and then when you export the EPUB file, make sure that the formatted option is selected in the images category of the export dialog box. All right, I'll go back to InDesign, and this time I'll crop this image. I'll also rotate it just to show you that when I export this EPUB file with that formatted option selected, that formatting is preserved.
But watch what happens if I export this without the formatted options selected. All that formatting is lost. The image is exported 100% of its original size. So it's way too big to even fit within the page and most of it is being cropped out. So as you can see, that little formatted option is quite important.
All right. So , now you know how wide a normal image should appear. But what about full screen images? I'll go ahead and undo this, Command or Ctrl+Z. Full screen images should be about 600 pixels wide by 800 pixels tall, which is exactly the resolution of most dedicated e-book readers. I'll go ahead and resize this image to those dimensions. I'll first fit the page into the window by pressing Command or Ctrl+0.
And then, I'm going to deselect this link icon so that the proportions are not constrained. And then, I can type in those exact dimensions, 600 by 800. I'll press Enter or Return to apply that. I'll move this image within the center of the page, and now, I'd like to fill the frame with the content by going up to the Object menu, choosing Fitting, and then, Fill Frame Proportionally.
All right, I'll go ahead and export this as an EPUB file. I'll replace the existing file. And in the Images category, I'll make sure and select the formatted option. I'll click Export. Now, I'm working on a resolution that's wider than it is tall, so this entire image isn't going to fit on the page, but on a typical dedicated e-book reader, this image would display well. In fact, on an iPad, an image that's 600 by 860 pixels will perfectly fit the entire screen.
I'll switch over to a sample e-book that I created specifically for the iPad. When I set up this image that we're looking at here in InDesign, I made it exactly 600 by 860 pixels, and as you can see, it perfectly fits the width and the height of the screen on the iPad. And when you flip the iPad horizontally, the image still fits the screen. And then, for both of these half page images, I made them 600 by 430 pixels. I didn't want to make them too tall, because I wanted to allow ample text to appear on the page with the images.
Alright, so, now you know the optimal size that your images should be scaled to and you understand the importance of using that formatted option when exporting an EPUB file. So now, I'll go ahead and explain how the other Image Export options work. I'll switch back to InDesign and I'll go ahead and export an EPUB file. So in addition to the formatted option, InDesign provides several other options for determining higher images or exported when the EPUB file was created. Now generally, you don't need to be so concerned with these options because InDesign actually does a good job choosing the right options for you. However, let me briefly explain how these work.
So, in the Image Conversion menu, you have a couple of choices. You can choose whether the optimized images are converted to GIF or JPEG, but if you choose automatic, InDesign will determine which format to use for each image in your layout. The GIF file format uses a limited color palette that can't exceed 256 colors. So it's really best used for logos and simple graphics. The JPEG format is best for images and illustrations.
If your InDesign document contains a combination of both logos and images, I highly recommend that you choose Automatic, otherwise, you can specify a specific format if you like. So, if a GIF file is created, InDesign will use these options here in the GIF options area to determine how the GIF file is created. There are really just two main options in this area. The Palette menu and the Interlace option.
So,the options in the Palette menu let you determine how you want InDesign to handle colors when optimizing GIF images, and if you select the Interlace option, it will speed up the download time of GIF images. Or in other words, it'll potentially speed up the time in which the image loads on an e-book reader, but this option also will increase the file size a little. Now, in my testing, I don't really notice a difference between this option being selected and not selected, so I generally leave it deselected.
I'm mainly concerned with the JPEG options. So, for image quality, I normally choose High, because I like high quality JPEG images. Now, in my testing I've discovered that there really isn't a difference between High and Maximum. When comparing the difference between images that were exported with the Maximum setting and the High setting, I discovered that the High setting gave me just as good of results and the images were slightly smaller in size. Within the Format Nethod menu, there are two options, Baseline and Progressive. Now, I haven't really noticed a difference between these two settings. So I just use the Default option.
Alright. I'll go ahead and Cancel this. One of the questions that I frequently get is whether or not you should use color or grayscale images in your e-books, since many e-book readers have grayscale screens. Now, I actually recommend that you use color images whenever possible. Although, many of the current e-book readers have grayscale displays, it's actually a good idea to use color images for two main reasons. So for one future, e-book readers will most likely have color displays. So, the e-books that you create today won't have to updated later on. And secondly, some e-book reading devices such as the Apple iPad, the iPhone, the iPad Touch, and various smartphones actually support color images. Now, I've just walked you through the process of exporting images from InDesign CS5.
I'd like to point out that InDesign CS4 actually has one other option that InDesign CS5 doesn't have. So, I'm going to switch over to InDesign CS4. And from the File menu, choose Export for Digital Auditions to create an ePUB file. And in Images area, I'd like you to notice that there's a Copy Images menu. So this menu isn't available on InDesigns CS5.
It has two options, Original and Optimized. If you choose Original, the original images are exported to the EPUB file. Now, keep in mind that when producing a document in InDesign, you typically use high resolution images. So if you try to use the same images for an e-book, they'll most likely be way too big. And large images consume a lot of memory and they actually take longer to draw on screen.
If an image is too large, you'll actually encounter problems on e-book readers that have limited memory and processing power. So I highly recommend that if you're working with InDesign CS4, choose Optimize and let InDesign automatically export an optimized version of the images for you that display well on most e-book readers. All of the other options in this category are the same as they are in InDesign CS5.
All right, now, I've just covered a lot of material. But, let me just summarize the main points that you need to remember. First of all, work in the Points Measurement System or the Pixels Measurement System. Resize your images to the size that you would like to see them in an e-book reader. For average images, they should be between 300 and 600 pixels wide. For full screen images, they should be 600 pixels wide by about 800 pixels tall. And then, when you export the EPUB file, make sure and select the formatted option in the Images category, and then, I like to choose Automatic for image conversion, and for the image quality, I select High. And that's all there is to it.
- Exporting an EPUB file from InDesign CS4 or CS5
- What's inside an EPUB file?
- Editing an EPUB file in Mac OS X or Windows
- Laying out pages
- Working with text
- Exporting graphics
- Creating a table of contents or navigation guide
- Inserting metadata
- Creating scalable images
- Validating an EPUB file