[Scribus] File size using photos

jon info
Fri Apr 13 18:14:12 CEST 2007

> Does this mean (with regards to the image quality) that it is  
> better to save
> photos as .png's since it is a lossless format? Do .png's have a  
> better or similar
> image quality as un-altered .jpg's?
This is from wikipedia:
JPEG will produce a smaller file than PNG for photographic (and photo- 
like) images since it uses a lossy encoding method specifically  
designed for photographic image data. Using PNG instead of a high- 
quality JPEG for such images would result in a large increase in  
filesize (often 5?10 times) with negligible gain in quality.

PNG is a better choice than JPEG for storing images that contain  
text, line art, or other images with sharp transitions that do not  
transform well into the frequency domain. Where an image contains  
both sharp transitions and photographic parts a choice must be made  
between the large but sharp PNG and a small JPEG with artifacts  
around sharp transitions.

JPEG is a poor choice for storing images that require further editing  
as it suffers from generation loss, whereas lossless formats do not.  
This makes PNG useful for saving temporary photographs that require  
successive editing. When the photograph is ready to be distributed,  
it can then be saved as a JPEG, and this limits the information loss  
to just one generation. That said, PNG does not support Exif image  
data from sources such as digital cameras, which makes it problematic  
for use amongst amateur and especially professional photographers.  
TIFF does support it as a lossless format, but is much larger in file  
size for an equivalent image.

JPEG has historically been the format of choice for exporting images  
containing gradients, as it could handle the color depth much better  
than the GIF format. However, any compression by the JPEG would cause  
the gradient to become blurry, but a 24-bit PNG export of a gradient  
image often comes out identical to the source vector image, and at a  
small file size. As such, the PNG format is the optimal choice for  
exporting small, repeating gradients for web usage.

Comparison with TIFF

TIFF is a complicated format that incorporates an extremely wide  
range of options. While this makes TIFF useful as a generic format  
for interchange between professional image editing applications,  
supporting specific applications such as Web browsers is difficult.  
It also means that many applications can read only a subset of TIFF  
types, creating more potential user confusion.

The most common general-purpose, lossless compression algorithm used  
with TIFF is LZW, which is inferior to PNG and, until expiration in  
2003, suffered from the same patent issues that GIF did. There is a  
TIFF variant that uses the same compression algorithm as PNG uses,  
but it is not supported by many proprietary programs. TIFF also  
offers special-purpose lossless compression algorithms like CCITT  
Group IV, which can compress bilevel images (e.g., faxes or black-and- 
white text) better than PNG's compression algorithm.



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