Summary
The management of images for an ebook can overlap with the management of images for a print version, but there are key differences when it comes to file types, color settings, the handling of cover images, and more.
Uploading Images to the Digital Hub
By default, images are processed as JPEGs with a maximum width and height of 600 pixels.
An image marked as the cover is processed with a maximum width and height of 1,800 pixels.
Image settings can be turned off or changed for all images in the Global Image Settings panel when uploading files.
The settings panel for an individual image can be opened by clicking the gear icon for that image.
Additional information about the Digital Hub’s processing of images can be found here.
Note: Some common file types used in typesetting (EPS, PDF, AI) cannot be uploaded to the Digital Hub. Files should be converted to JPEG before uploading to the Hub.
Cover Images
Identifying an image as the cover in the Digital Hub changes the max width and max height settings from 600 to 1,800 pixels.
If an image is named with “-cover” in the file name (e.g., scr-project-cover.jpg), the Digital Hub will automatically set it as the cover.
Otherwise, to set the cover image, select the “set cover” option when uploading the file. This option is also available after a file has been uploaded.
As long as a cover image is uploaded to and specified in the Hub, the cover will display properly in the ePub with no need for any manual intervention.
Default Alt Text for Covers
If there is no alt text specified for the cover, the Digital Hub will add “Cover Page for [Book Title]” as alt text in the ebook’s HTML. The book title is pulled from the Title field in the Digital Hub, not text in the ScML file.
Customized Alt Text for Covers
Scribe recommends using the default “Cover Page for [Book Title]” alt text.
If customized alt text is needed, it can be added to a “cvi” chapter.
If there's a “cvi” chapter, the Hub will use that for the cover image.
<chapter id="cvi">
<cover><fig><img src="title-cover.jpg" alt="Customized alt text."/></fig></cover>
</chapter>
Grayscale vs. Color (Image Management)
If color images are available, Scribe recommends using them in the ebook, even if the print version uses grayscale versions.
Images Used Instead of Live Text
Scribe recommends using live text for any text-based element (e.g., a half-title or title page).
If an image is used in place of the live text, that image needs to have alt text associated with it.
Images should not be used as a replacement for text when Unicode characters are available. This includes foreign languages and mathematical text.
Image Size and DPI
Do not use DPI (dots per inch) as a measure of the “quality” of a digital image. DPI is a piece of metadata that tells a printer how big to print an image or a scanner how much detail to capture when scanning. When downsizing an image to 600 pixels, that pixel count is the limiting factor in terms of preserving image detail (quality).
Images resized through the Digital Hub are not guaranteed to end up with a specific DPI. The DPI or PPI (pixels per inch) of an image cannot be specified when resizing through the Hub. If images are processed and resized outside of the Hub, turn off image processing when uploading files.
Using the Hub, however, a user can change the dimensions of a file. When resizing an image down, the pixel dimensions of an image control how much information is retained in the image. The smaller the width and height, the less detail that will be retained. A reader’s monitor or device settings typically control how many inches an image takes up on the screen, not the DPI/PPI metadata.
Image Cropping
Images should be cropped properly in order to display the same content in all editions. If a print version exists, images should be checked to confirm that portions have not been masked in InDesign.
Images in a Gallery
Image galleries need not be mentioned in a print book’s table of contents. If mentioned as a TOC listing, however, or through a statement like “A photo gallery follows chapter 9,” this should be addressed when preparing the ScML file for conversion to the ePub format.
In a TOC, Scribe recommends placing a new gallery listing as the last chapter before the back matter and naming it simply (e.g., Photo Gallery, Image Gallery, Figure Gallery).
<toc id="rgallery"><xref idref="gallery">Photo Gallery</xref></toc>
Comment out any reference in the print version to a page number.
<!-- <tocf><i>A photo gallery follows page 76.</i></tocf> -->
The gallery itself should have a chapter title and then each of the figures.
<chapter id="gallery">
<ct><xref idref="rgallery">Photo Gallery</xref></ct>
<figure>
<fig><img src="scr-project-fig0101.jpg" alt="Alt text here"/></fig>
<figcap>Figure caption text.</figcap>
</figure>
Directional Language
References to images should avoid directional language, instead prioritizing mentioning the image name directly. This provides a clear path to the image in all environments. Phrases like “in the figure below” or “in the above image” should be avoided in favor of phrases like “in Figure 1.1.” The explicit indication of the figure name can then be used as a link to the image.
Similarly, directional language used in a print version to refer to side-by-side images would also need to be reworked when the images are no longer placed in that arrangement for a digital version. This is best handled when editing a manuscript by using language that does not depend on the arrangement of the images. Directional language should be reviewed when preparing the ScML so that any changes can be implemented before processing the file to the ePub format.
Concrete Poetry (Special Spacing or Shapes)
Some variation is to be expected and accepted when displaying poetry in an ebook.
If poetry contains special spacing between words, use nonbreaking spaces (not regular spaces or tabs).
The amount of space between words in a digital environment will not necessarily match what is seen in a print environment, in which spacing and turnovers can be handled more exactly.
If the shape of a poem is crucial to the author’s intention (known as “concrete poetry,” such as a poem about an apple that is shaped like an apple), an image may need to be used. However, to make this accessible, additional steps should be taken.
- Add alt text that indicates the image is in a particular shape.
- Follow the image with the live text of the poem, including a disclaimer to indicate this is the text, disconnected from the shape of the poem.
Further information about how to work with shaped poetry can be found here.
Image Processing
Programs
The Digital Hub uses open-source image libraries to perform image conversions. Details about Digital Hub image conversions can be found here. For best results, Scribe recommends performing image conversions locally before uploading files to the Digital Hub.
The three main programs Scribe uses for image processing are Photoshop (Mac or PC), Gimp (Mac, PC, Linux), and IrfanView (PC only). Gimp and IrfanView are both free. Following a free trial, Photoshop is a subscription-based product in Adobe’s Creative Cloud.
Image Size
Body Images
Best Practice: Scribe’s current default is to set the maximum size for an image to 600x600 pixels (or 600 pixels on the larger side). This prevents the images from being cut off on devices that do not support larger image sizes.
However, larger images (up to 2000x2000 pixels) should be used for text heavy images, maps, and other images with aspects that would benefit from the increased size.
Cover Image
Best Practice: Set the maximum size of a cover image to 1800 pixels on its largest side. (No side should ever be smaller than 500 pixels.)
Settings
DPI
Scribe recommends using a consistent DPI of between 120 and 300 for all images.
Colorspace
Change color to RGB (rather than CMYK) format.
CSS
Standard Images
Scribe adheres to a 600x600 pixels maximum size for images. If using Scribe's default CSS, these standard images will be handled properly, without issue.
Oversized Images
When using oversized images (e.g., for text-heavy images that need to remain legible) use a custom CSS in order to prevent the images from being cut off or spanning across multiple pages on some devices. Scribe uses percentages to control the appearance of these larger images across devices:
- img.tall {height: 95%;}
- img.wide {width: 95%;}
- img.full {height: 95%; width: 95%;}
Apply the “tall” setting to images taller than 600 pixels, “wide” to images wider than 600 pixels, and “full” to images both taller and wider than 600 pixels. In the HTML file, give the image a class value that corresponds to the appropriate CSS callout. For example,
<p class="fig"><img class="tall" src="images/scr-projectcode-fig1.jpeg" alt="" width="500" height="900"/></p>
Photoshop Batches
A tutorial that provides step-by-step instructions for batch processing in Photoshop can be found here.