[Scribus] File size using photos
Sat Apr 14 18:27:41 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.
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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