|
|
Photo JPEG
Overview
The Photo JPEG codec implements the Joint Photographic Experts Group (JPEG ISO version 9R9) algorithm
for image compression. It is generally used for storage of still images. It can also be used for editing
and storage of high-quality video files.
There are three JPEG-based codecs built into QuickTime. They
are Photo JPEG, MJPEG-A, and MJPEG-B. MJPEG stands for "Motion JPEG," and is indentical to
Photo-JPEG except that the MJPEG codecs have translators built-in to support the different capture cards.
We will only discuss the Photo-JPEG codec here; MJPEG-A and MJPEG-B have their own section.
Architectures Supported
Pros
- Picture quality is generally good enough for use in desktop publishing
applications.
- This codec is great for compressing high-resolution, photographic images,
and is also very good for 8-bit grayscale images.
- It works very well for "slide-show" movies that have a very
low frame rate.
- It has some application for Web video, although other commercial codecs
are often preferable for most movies.
Cons
- The Photo-JPEG codec requires significant amounts of CPU power and
is not well suited to CD-ROM or higher data rates, except when assisted
by a hardware capture card.
- Large image and/or high frame rate movies usually don't play smoothly.
- If the same file is saved multiple times, the JPEG artifacts may build
up and become objectionable.
Tips
- If you are delivering a CD-ROM based title which will require a Quadra
class system (or faster) to run, you can use the Photo-JPEG-compressed
QuickTime movies to store your 24-bit backgrounds to increase performance.
- Avoid saving the same file multiple times (see above).
| Ideal source material |
Photographs |
| Supported bit depths |
24-bit color, 8-bit greyscale |
| Compression time |
Asymmetrical |
| Temporal compression? |
No |
| Special features |
Supports Media Cleaner Pro 2.0's advanced data rate limiting |
| Encoder requirements |
Any MacOS or Windows |
| Decoder requirements |
Any MacOS or Windows |
| Encoder availability |
Built into QT |
| Decoder availability |
Built into QT |
| Algorithm |
Discrete Cosine Transform (DCT) |
| Manufacturer |
Apple |
If you have any comments or tips & tricks to share
about Photo-JPEG, please contact us at
info@terran-int.com.
|
