Recommended graphic file format for single-sourcing from Frame to Robohelp?

[Combs, Richard]

John Sgammato wrote:
 
> With all due respect to my colleagues on this forum, IMO the line
> between JPG and other formats is no longer as neat as it once was. Many
> screenshots in Win 7 require gradients that JPG handles well. IMO
> anything that a photo can handle might not be so far removed as you
> might think from basic screen captures, We are no longer in the
> cartoony Win 3.x world.

Text rendering is more important in most screenshots than cool gradients (which, in any case, PNG handles better than JPEG; see below). I prefer that text not look like someone smudged the ink before it dried. 

Wikipedia has a composite image that shows the difference here: 

http://en.wikipedia.org/wiki/Portable_Network_Graphics#Comparison_to_JPEG 

Here's their comparison: 

"JPEG (Joint Photographic Experts Group) format can produce a smaller file than PNG for photographic (and photo-like) images, since JPEG uses a lossy encoding method specifically designed for photographic image data, which is typically dominated by soft, low-contrast transitions, and an amount of noise or similar irregular structures. Using PNG instead of a high-quality JPEG for such images would result in a large increase in filesize with negligible gain in quality. By contrast, when storing images that contain text, line art, or graphics - images with sharp transitions and large areas of solid color - the PNG format can compress image data more than JPEG can, and without the noticeable visual artifacts which JPEG produces around high-contrast areas."

As for gradients: 

"Early web browsers did not support PNG images, JPEG and GIF were the main image formats. JPEG was commonly used when exporting images containing gradients for web pages, because of GIF's limited color depth. However, JPEG compression causes a gradient to blur slightly. A PNG file will reproduce a gradient as accurately as possible for a given bit depth, while keeping the file size small. PNG became the optimal choice for small gradient images as web browser support for the format improved." 

> And since AFAIK FrameMaker still imports eleventyhundred colors with
> every .PNG file, I do not see why a PNG with its headaches is superior
> to the no-longer-extant difficulties of the .JPG format.

You only get the named RGB colors (like "RGB 000,070,136") in FM if you import indexed-color (AKA palette-based) PNGs. Each color in the PNG's palette (up to 256) is added to FM's color definitions (the name specifies the R,G, and B values that define the color). A different 256-color PNG may have different colors in its palette, so each can potentially add up to 256 colors to FM's list.

To avoid this problem, simply use Truecolor (AKA 24-bit) PNGs; they're not that much bigger.  


Richard G. Combs
Senior Technical Writer
Polycom, Inc.
richardDOTcombs AT polycomDOTcom
303-223-5111
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rgcombs AT gmailDOTcom
303-903-6372
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