[Scribus] File size using photos

Nigel Ridley nigel
Sat Apr 14 18:27:41 CEST 2007

jon wrote:
>> 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.
> ----
> Jon

That is useful to know - thank you.

So in brief, it is recommended to save the original .jpg as a .png, then do all 
ones editing then save as a .jpg again for use in whatever_application.

Would the quality of the original .jpg suffer visibly in a finished [Scribus] .pdf 
if I only cropped it (one edit and one save - ie. one generation) and re-saved 
(using the Gimp) at 100% ?



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