Re: [OT] Digital camara

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Les wrote:

Jpeg is a horrible compression algorithm.  I have no idea why it was
chosen.  It is lossy, has artifacts in the result, often smearing the
image or showing a fingerprint like Moire pattern (most image processing
software has an anti-moire filter specifically tailored for JPEG ) and
other artifacts.  There are better compression algorithms, but many if
not all are proprietary.  Somewhere in Europe about 2005, there was a
new lossless algorithm similar to LZ in compression size or slightly
better, and HP licensed it, but I don't know the name.  LZ and GIF are
also lossless, but GIF somehow lost the ability to do color from what I
understand.  The problems endemic with images deal with the
representation, and the problem with something called tilt, which is an
artifact of the digital image capture method from CCD's.  CMOS devices
don't exhibit this or at least don't have to because the underlying
technology is different.

Any image format is a compromise between conflicting needs. You want an image format that expands without practical limit? You need an algorithmic format. It's what postscript (without bitmaps) does.

You want an exact image to some defined precision. Choose dots per inch in two dimensions plus some number of bits per pixel to represent colour: 8 bits (256 colours) is generally regarded as pretty horrible.

That's what a bitmap does, and it uses a lot of storage space. Images are compressible to varying degrees depending on the amount of detail they contain.

JPEG is a compromise, chosen because it's more compressible, at some loss of detail. The amount of compression is selectable, and the more compression the more loss of detail.

It's used because it can give good compression, and in many cases the lost detail doesn't matter too much. JPEG images out of my cameras look fine on my computer. My Canon claims to be able to store around 1000 photos at its highest resolution on my 4 Gb CF card. However, if I want to get the best quality images my camera can do, I use its native format, called "raw," and store many fewer images on the CF card.

According to my camera's handbook, raw images occupy about 8.7 Mbytes at its highest resolution. I have several choices with JPEGs, the best quality & largest takes 3.8 Mbytes


Some image compression algorithms are described as "lossless," meaning that they preserve the original detail.

Others, such as that used in JPEG, are lossy - they sacrifice detail to save on storage.

Poor image quality is more likely to result from use of digital zoom. Here is one pixel at the camera's native size.
.
Here is the same picture, zoomed to twice the linear size:
..
..

Properly scaled, it's a square box.




--

Cheers
John

-- spambait
1aaaaaaa@xxxxxxxxxxxxxxxx  Z1aaaaaaa@xxxxxxxxxxxxxxxx
-- Advice
http://webfoot.com/advice/email.top.php
http://www.catb.org/~esr/faqs/smart-questions.html
http://support.microsoft.com/kb/555375

Please do not reply off-list

--
fedora-list mailing list
fedora-list@xxxxxxxxxx
To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list
[Index of Archives]     [Older Fedora Users]     [Fedora Announce]     [Fedora Package Announce]     [EPEL Announce]     [Fedora Magazine]     [Fedora News]     [Fedora Summer Coding]     [Fedora Laptop]     [Fedora Cloud]     [Fedora Advisory Board]     [Fedora Education]     [Fedora Security]     [Fedora Scitech]     [Fedora Robotics]     [Fedora Maintainers]     [Fedora Infrastructure]     [Fedora Websites]     [Anaconda Devel]     [Fedora Devel Java]     [Fedora Legacy]     [Fedora Desktop]     [Fedora Fonts]     [ATA RAID]     [Fedora Marketing]     [Fedora Management Tools]     [Fedora Mentors]     [SSH]     [Fedora Package Review]     [Fedora R Devel]     [Fedora PHP Devel]     [Kickstart]     [Fedora Music]     [Fedora Packaging]     [Centos]     [Fedora SELinux]     [Fedora Legal]     [Fedora Kernel]     [Fedora OCaml]     [Coolkey]     [Virtualization Tools]     [ET Management Tools]     [Yum Users]     [Tux]     [Yosemite News]     [Gnome Users]     [KDE Users]     [Fedora Art]     [Fedora Docs]     [Asterisk PBX]     [Fedora Sparc]     [Fedora Universal Network Connector]     [Libvirt Users]     [Fedora ARM]

  Powered by Linux