"So, I
took my family on vacation to Disneyland and just like thousands
of other people I took my digital camera. I took about 300 picture
and thought it would be great to make a montage that I could
edit and send to my family members on DVD. So I copied all my
JPEGs from my MemoryStick on to my hard drive and opened up my
NLE. After I imported them into my project I started to notice
some erratic behavior, until my machine finally locked up! What's
going on?"
Well, folks, this is one of
those stories that I've been hearing almost once a week for several
years now. How do you deal with digital photos when you are working
with a video project?
System overload
The most common problems caused
by using many JPEGs in a video project is that your NLE's allocated
memory might be filling up or the system resources might be taxed
by having to open all the JPEGs to memory. Either way, the symptoms
can present themselves as overall slower performance, NLE instability,
or even whole system shutdown. This happens in most cases because
the files are just too big. Having to actually uncompress the
JPEG file just adds extra work too. By sizing your photos correctly
and importing them into the NLE as an uncompressed format most
photo-related problems can be prevented.
Sizing your photos
In the case of a DV video project
the video is comprised of approximately 30 frames per second.
Each of these frames is 720 pixels wide and 480 pixels tall.
In an uncompressed format, each of these frames takes up about
1MB of memory. When photos are imported into the NLE, the NLE
will take the photo and make it fit into the 720x480 frame size
and then display it for what ever duration it is set to play
for. That's right, no matter how big our small our photo is the
typical NLE software will automatically resize the image to fit.
Let's look at some standard digital camera image dimensions to
see what this means:
2MP digital image - 1632 x 1232 pixels - That means
that the uncompressed image takes up about 6MB. That's 6 times
the memory needed for a single video frame.
3.1MP digital image - 2048 x 1536 pixels - That means
that the uncompressed image takes up about 9MB. That's 9 times
the memory needed for a single video frame.
5MP digital image - 2560 x 1920 pixels - That means
that the uncompressed image takes up about 15MB. That's 15 times
the memory needed for a single video frame.
8MP digital image - 3264 x 2448 pixels - That means
that the uncompressed image takes up about 24MB. That's 24 times
the memory needed for a single video frame.
As you can see, today's cameras
deliver an impressive pixel count and are fantastic for printing
photos even at large sizes. Putting them on the video timeline
is a little overkill though. Depending on the NLE, the application
will either store the picture in memory waiting for it to play
or will load it into memory as it encounters the image on the
timeline. Either way it takes up a lot of extra memory and system
resources. If too many pictures are loaded into memory this can
really bog things down. If you don't believe me try opening up
a hundred pictures in Photoshop, which is optimized for photo
images, at the same time and see how your system behaves.
My recommendation - Before you bring all your digital
pictures into your NLE size them appropriately. I recommend sizing
them as close to the target frame size as possible. For DV this
means 720x480. Be aware that since DV's aspect ratio is .9 pixels,
you will actually want to resize down to 720x540 and then squeeze
the image to 720x480. The best way to resize hundreds of photos
is to create a script or action inside of your image editing
software and automate the process. There is an exception to this:
If you plan on using your NLE to animate photos and/or zoom into
them you'll want to make sure you have enough extra pixels in
the image to prevent scaling. Better yet, do your animations
in an application designed for this purpose like Canopus
Imaginate
or Adobe After Effects.
Uncompress the JPEGs
At this point, many people
start to tell me that their 8MP picture only takes of 6 or 7MB
on the hard drive. This of course is true due to the wonder of
digital compression. JPEG compression is the most popular image
compression format and is used by almost every digital camera
manufacturer to store captured images. While this is great for
enabling the photographer to store hundreds of photos on a small
chip, printing or displaying the image require that the JPEG
be uncompressed. Before any JPEG can be played back from the
timeline of the NLE, the application must uncompress the file
and load it into memory. This is similar to the way a ZIP file
works -- you must unZIP it to access the compressed files. Saving
the files in an uncompressed format like BMP or TGA will save
your NLE from the overhead of having to load the files into memory.
I recommending making this part of the same automated script
that you use to resize the pictures.
While it may seem like a lot
of work to resize hundreds of pictures and save them in an uncompressed
format, most of it can be done automatically with an image editing
application like Photoshop. Besides, the amount of time it takes
should balance with the increased performance of your video project.
Ashley
