According to the age-old adage, “A picture’s worth a thousand words.” That may be true in terms of how much writing it would take to describe what is shown in a picture.

However, when it comes to file size, this equation doesn’t hold true. Instead, a single picture may equate to tens or hundreds of thousands of words.

Each letter in a word uses one byte of memory. A small, simple JPEG picture that measures about 200 pixels by 200 pixels might have a file size of about 10 to 20 kb, where each kilobyte (kb) is 1000 bytes. A simple JPEG picture that measures 1200 x 1600 pixels might have a file size of hundreds of kb. Higher resolution images or rich formatting may easily drive the file size into megabytes, where each megabyte (Mb) equals 1000 kb or 1,000,000 bytes. (Note: k = kilo = thousand, M = mega = million. You wouldn’t mind earning a M$ from your royalties, for example.)

If a word is about 5 letters long, on average, this means that a simple 200 x 200 JPEG picture takes as much memory as about a few thousand words, a 1200 x 1600 JPEG picture equates to about a hundred thousand words, and higher-resolution or richly formatted pictures are worth nearly a million words.

Why does this matter? This affects both publishers (including self-published authors) and readers of eBooks. First, there is a maximum size on the content file of an eBook – for Kindle, it is 50 Mb, and for Nook, it is 20 Mb. An eBook that features many large, high-resolution, richly formatted pictures is in danger of exceeding this limit.

Secondly, the content file size may affect the list price and royalty. For example, with Amazon’s Kindle, an eBook can only have a list price of 99 cents if the content file size is below 3 Mb and a list price of $1.99 if the content file size is below 10 Mb; otherwise, the minimum list price is $2.99. If you want to sell a Kindle eBook for less than $2.99, you must keep the file size below these thresholds.

Also, Amazon deducts 15 cents per Mb from the list price before applying the royalty percentage for Kindle eBooks on the 70% royalty option. For example, suppose that you have a 10 Mb eBook that you want to sell for $4.99 on the Kindle. The file size deduction is $0.15 x 10 = $1.50, which means that the royalty is ($4.99 – $1.50) x 0.70 = $3.49 x 0.70 = $2.44. If the file size could be reduced to 5 Mb, the royalty would be increased to $2.97. In this example, saving 5 Mb of file size adds 50 cents to the royalty. For every 1000 books sold, this amounts to $500.

The effect of pictures on file size affects both customers and publishers. Customers appreciate pictures, especially if they have a color eReader like the Kindle Fire or Nook Color. They also like the pictures to have high enough resolution to see the image clearly on any device (from a tiny iPhone to an iPad) and to be formatted well. However, including more pictures also affects the price of the eBook, and – another important consideration – the delivery time of the download (the delay is even longer for older eReaders).

There is a trade-off between the benefits of including many high-resolution pictures and the disadvantages this has in terms of list price eligibility, royalty, and delivery time. The publisher is faced with a difficult challenge to balance this properly.

However, there are a few ways to decrease the size of the content file for the eBook. Keep in mind that you don’t want to sacrifice image quality in the content file for a paperback book, so you need to have two separate content files for your book – one for the eBook and another for the paperback.

In Microsoft Word, right-click on any picture in your content file, choose the Format tab at the bottom of the page, select Format Pictures, uncheck the Apply Only To This Picture box, and select a Target Output (if you have an older edition of Word, like 2003, the instructions are a bit different). E-mail resolution (96 ppi – pixels per inch) will give you the minimum possible file size, and is generally suitable for eReaders. I suggest saving your file with different names before and after trying this so that you still have the original.

Paperback books have the opposite problem. If you submit content and cover files to CreateSpace, for example, a common error is that a picture has a DPI (dots per inch) of less than 200. You want high resolution images on your paperback book, where there is a generous maximum content file size of 400 Mb.

Note the distinction between resolution and DPI. The resolution of a picture is based on how many pixels it measures across and high (like 600 x 800, which is common for full-screen images on eReaders), whereas DPI measures how many dots there are per inch on the printed page. The size of the picture in addition to the resolution affect how many pixels will span one inch.

Coincidentally, there are about 930 words in this blog article. So this blog is equivalent to a single picture – or about a tenth or hundredth of one in modern terms. Picture that!

Chris McMullen, self-published author of A Detailed Guide to Self-Publishing with Amazon and Other Online Booksellers (Volume 2 coming in mid-April)