June 1999
Intermediate to advanced
340 pages
10h 10m
English
Content preview from PNG: The Definitive GuideBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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Chapter 5. Applications: Image Converters
Conversion to PNG from other image formats (or even from PNG) remains a popular approach for the simple reason that other formats have traditionally been better supported by applications. Even with good, current application support for PNG, users typically have large archives of older images, at least some of which may they desire to convert to PNG format.
Just as one would like to see certain basic PNG features supported in image editors (which may be thought of as a special case of conversion utilities, converting and optionally modifying a previously saved image file) one would like certain basic PNG features supported in converters. These include:
- Preservation of basic image types: RGB, grayscale, and palette-based
- Option to convert “truecolor” images with fewer than 256 colors to palette-based (or grayscale, if appropriate)
- Preservation of simple transparency in palette images (e.g., when converting from GIF), including the ability to reorder the palette so the transparent entry comes first, which avoids wasting space in PNG's transparency chunk
- Preservation of unassociated alpha transparency (e.g., when converting from TIFF)
- Preservation of gamma, chromaticity, sRGB, or full ICC profile information (see Chapter 10, “Gamma Correction and Precision Color”, for details)
- Option to preserve “deep” samples, such as from 12-bit JPEG or medical images or 16-bit-per-sample TIFF images
- Preservation of text information (e.g., from JPEG, GIF, ...
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