Weird problem with jpg cover

[AlexBell]

Please bear with me: this is a longish post but it will take some time to explain the background and what I've already tried.

I design ebooks for Circaidy Gregory Press, and have a set of template files that I use depending on what kind of an ebook it is. I get the original text as a doc file, markup the text as XHTML 1.1 files and slot the text into the templates. I also get the cover images sent to me by the editor, and slot them into a cover page.

Yesterday I got an attached jpg and put it into Coverpage.html, and when I'd done an early layout draft validated the XHTML and the images into an ePub, which I validated with EPUB-Checker.exe. But when I did a rough check using the Sony desktop reader the cover did not show - there was just a blank page. I uploaded the ePub into calibre, checked the file with the calibre viewer, and the cover did show. I downloaded the ePub on to my Sony T1 and Nexus 7 (via Calibre Companion) and found that the cover did not show on either reader - just a blank page.

After some frantic checking of the markup in Coverpage.html and testing I eventually took out the new cover image, and used a cover jpg from an earlier ebook and changed the content.opf accordingly using exactly the same markup as I started with. The old cover showed just as one would expect - there was no problem. I then recompiled the ebook with the new cover jpg, and had exactly the same problem - the image did not show.

I then took the new image which I hadn't been able to make work, opened it in GIMP to get the xcf file, and then exported thexcf image in jpg and png formats. I used both of them in the ebook (one after the other), and both of them worked.

So my best guess is that there was something in the new cover image sent from the publisher, and that putting it through GIMP fixed whatever it was. Does that make any sense? Could some kind soul use the attached image as is to see if it works on your reader? If the fault is in the image itself is there some way of checking images to make sure they will work on a reader? I must admit that I know very little about images - just enough to get by.

The attached image is copyright 2013 to Catherine Edmunds. She has given me permission to attach the image to this post, but retains the copyright. The image must not be used for any other purpose without her knowledge and consent.

[dwig]

I'm not in a position right now to build this image into an ebook and test, but I did download the image than inspected it in Adobe Bridge. I suspect the issue stems from this image being CMYK and, quite possibly, it is failing in some readers that only support RGB color space. In your experiment with GIMP the image may have been converted from CMYK to RGB as a result of some default settings in GIMP's JPEG and PNG export functions.

[AlexBell]

Thanks, dwig, that's most helpful. Now to google CMYK.

[dwig]

Originally Posted by AlexBell

Thanks, dwig, that's most helpful. Now to google CMYK.

I suppose you've found what you need, but for the sake of lurkers:

CMYK (Cyan Magenta Yellow blacK) is the 4-color colorspace used by most printing processes, particularly offset printing. It is also the colorspace used by the marking engine (that part that actually marks the paper) in common inkjet printer although their firmware and drivers are designed to swallow RGB (Red Green Blue) colorspace images.

RGB is the 3-color colorspace commonly used for digital capture and display. The output from digital cameras is generally converted from their raw sensor data into RGB images (TIFF or JPEG) either in-camera or using external conversion software (e.g. Lightroom, Aperture, Photoshop w/ Adobe Camera RAW plugin, ...). Computer monitors also work in the RGB colorspace.

For these reasons RGB is the commonly used colorspace for computer images while CMYK is the commonly used colorspace for artwork and images intended for output on printing presses.

The CMYK cover image is likely the result of the graphic image being originally created for use on the pbook's cover and not specifically created for the ebook. It is generally a simply matter to use an image editor that supports both RGB and CMYK to open the CMYK image, convert it to RGB, and then resave it. Conversion can result is some colors changing. A good program, like Photoshop, will offer the ability to select the color profile (ICM) and rendering method to help minimize the changes.

I've attached a copy converted to RGB

[AlexBell]

Thanks again, this time for the information which was much easier to understand than the other sources I found.