Working with Bitmap Images

It's not as confusing as it seems...

So, should I use that jpeg image or a png? What about the tiff image? What is a gif? It gets a bit confusing as the image formats and specs seem to shift in and out of popularity, not to mention the specs required by various producers of eBooks. Well, in the beginning, was the GIF -- Graphics Interface Format. Originally (back in the misty days of Compuserve and dial-up networking) the gif was a very simple graphics format to create 8-bit color images that could be seen similarly on a range of the currently available graphics color monitors. They weren't the animated short-loop images we now associate the format with. Just simple static graphics. Only a short few months before, the only monitors were text-only monstrosities using a Cathode Ray Tube (TV Tube) in an extended case. They tended to run hot and could color the ext that scrolled in day-glo green, or sometimes red. Moving to a color monitor was like opening the door to the world. The only problem was that color images were large files. They took a long time to download. In those days, a big hard drive had 20 Megabytes of storage. I had two of those running on my i286 machine. Color reduced and compressed to 8-bits were still better than the alternative. Finding ways to keep file size down while not making the resulting images look too ridiculous was the challenge of the day. Soon, JPEG 16 bit color image formatting was possible. Much closer to real, but bigger files. Image compression now referred to as "lossy" compression (as it degraded the absolute details and color fidelity) was used to make adequate-appearing, smaller files that would download reasonably quickly over a telephone line connection. Once image manipulation software was available, things started to get really weird as new formats were experimented with constantly. Images went from 16 to 24 bits to capture the equivalent of 16 Million colors, closer still to real. Faster processors and better BIOS systems meant faster download speeds, too. Soon additional compression-less formats emerged, such as TIF files. These were immense files, but truer still to real. Spring ahead through some more misty years and you find yourself in our current iteration. As a publisher, you need to know a few of the terms being tossed around. First, there is a difference between the two different color models you'll be making use of. Reflective light, as in color reflected from a surface such as printed paper, and color passed through transmission from a source to your eyes. RGB (from the three colors of transmitted light in a monitor: Red Green and Blue) 24-bit and smaller images are fine for transmitted light (your brain fills in the rest), but for color fidelity from a reflected surface, you need to use 32 bit images. These are also known as CMYK images from the four colors of ink in Process Color Printing: Cyan, Magenta, Yellow and blacK. But wait... now KDP isn't calling for CMYK 32 bit cover images any more. Now they want RGB images. They must be doing their own conversions and besides, most proofing is now online (using transmitted light) so it makes for smaller, more easily uploaded files in JPG, TIF and PDF formats. I generally now use 32-bit tiff files, converted to full page (original size) pdfs for print covers. RGB files are perfect for Kindle and other eBook format covers as well as online advertising and listings.

But, if this is beginning to sound like an endless list of techhie stuff to learn, there is really just a couple more basic concepts you need. First, Re-sampling. Even the simplest image editing software includes a way to re-sample images. It is the name for a way to re-size images without getting all jaggy and pixelated in the process. Re-sampling uses an algorithm to actually rewrite the entire image file into new parameters. The variables include the height, the width and the resolution needed. These days, with hard drive storage measured in Terabytes, larger files are not a problem to store. I recommend that all your production files for book graphics be in 300 dpi resolution. This would be either RGB or CMYK. Modern monitors can reproduce this resolution without any of the old issues of pixelated break-up that were common... back in those misty days long gone. FB, for example, now recommends 300 dpi files that are around 3" on the short side to produce a file of between 2.6 and 3.4 Mbytes. Now, that is a reasonably instant up or down load. If, for some reason, you need to produce lower resolution images, you can do so from the 300 dpi stored original image using re-sampling with no loss of detail. For what it's worth, old-time monitors couldn't reproduce an image at more than 72 dpi resolution, so we've really come a long way! Last thing, practice, practice, practice. Play with lots of images and resample them to your heart's content. Differing color models, resolutions and other massages, such as contrast, sharpness, etc. Train your eyes, then trust them. It's not that hard.