Vision Unlimited/LA News

Digital Stills and Video

by on Aug.16, 2009, under Opinion, Tech Notes

People often ask me what they need to know to shoot “digital” and what is different about shooting electronically from shooting with film. Here are a few thoughts.

The rapid developments in digital technology make the answer different every time i try to explain it. Resolution of electronic cameras now rivals film cameras, although the highest quality digital cameras still cost 10 to 50 times as much as most of us are willing to pay for a camera. And good quality glass still defines the quality of still and motion pictures. How much you are willing to pay still determines how good your pictures will be.

Camera sensitivity is also improving, along with the dynamic range, the contrast that can be captured without losing dark and highlight details. And color reproduction and color control are getting better as well. You can now do things in-camera that were unheard of a few years ago, and the camera is often the best place to do those things because you usually have more information in the camera than you ever have after you save the picture to a card or disc.

These improvements are showing up in both motion and still cameras, and often the distinction is blurred between the two as more motion cameras also shoot stills and now many still cameras now shoot motion sequences.

The biggest distinction between shooting still and motion is the length of the exposure. Motion capture limits the length of each exposure to the time between the frames in the sequence, so a 30 frame per second clip is limited to a shutter speed of 1/30 second. That is a pretty long exposure and most scenes are shot with a shorter exposure to reduce the motion blur as objects move in the scene or the camera moves across a static scene. However, as in still shooting, longer exposures gather more light so there is a trade-off and if there is little movement to capture, a slow shutter can produce a cleaner and/or brighter image. For static scenes, still cameras can use even longer exposures to improve image quality even more.

Conversely, the improvement in sensitivity in electronic cameras and sensors allows shorter shutter speeds for moving scenes and reduces motion blur and image noise in still and motion shots.

Another continuing improvement is in the density of the storage media for cameras. For still cameras, that means more and larger files can be stored between off-loads. As processing speeds in cameras has improved, larger files with more resolution and RAW files without potentially degrading image compression can be recorded for later processing.

For motion cameras, higher quality video compression can be used, providing fewer compromises in image quality and more flexibility in post production because we can deliver more bits from the field into the editing system. However, newer compression schemes do not come without costs. Advanced compression schemes require higher performance processors, so even though your bit rate may be as low or lower than a previous version with lower quality, you may not be able to make use of it without upgrading your computing hardware.

Then there are differences in camera sensors. Most motion cameras before 2008 had CCD image sensors and prism optics for high quality RGB image capture, but this year, CMOS sensors have started to become popular. They can give you more sensitivity and offer promise for more improvements, but they also have some side effects that can be annoying, depending on your type of shooting.

Most CMOS cameras are provided with a “rolling shutter” to simplify sensor design and the rolling shutter can create image “artifacts” (unwanted effects) that may be distracting. Flash pictures may show up on only part of a frame, depending on when in the exposure time that it happens. Pans may have a skewing look because the top and bottom of the frame are scanned out at different times during the pan.

Whether these problems affect you depends on whether you shoot events where strobe photography is plentiful and whether you often pan across objects with vertical lines. The improved sensitivity of the camera may make up for any new issues created by the new technology.

The first thing that will help you get the most out of your camera is to get it into as manual a mode as possible. Cheaper cameras may not have much of a manual mode, but you can probably still convince the camera to favor one variable over another. It’s just a matter of understanding what the auto modes mean.

Portrait modes usually use longer exposure times to get more depth of field (focus separation between foreground and background) and cleaner images at the expense of motion blur. So if you can put your camera on a tripod, portrait mode may be good for static shots.

Sports modes usually shorten the exposure to freeze action and assume that you will have enough light to get an acceptable image.

Scenic modes may assume enough light and a wide lens angle so that motion blur and depth of field are not issues.

In a manual mode, you may be able to directly change the shutter speed and/or the aperture settings to experiment with different effects. You may also be able to adjust the sensitivity of the camera to light – the ISO setting – to change the amount of video noise or graininess in the images for the same image brightness.

Once you get the images to your computer, there is almost as much range in processing software as there is in cameras. Most cameras  come with some specialized software, and there are consumer and professional application programs, which can allow you to make big changes in image look, with or without serious side effects.

One thing to keep in mind when you are deciding how to capture and store your images is the amount of correction that you want to be able to apply in your processing software. Some cameras now allow you to store images with 16 bits of information per color, instead of the older 8-bit formats. JPEGs usually only provide 8 bits. That means only 256 shades of gray between black and white. That is just about enough for the human visual system to think that the shades are continuous but not necessarily enough to allow big changes in contrast or color. If you change too much, steps may become visible in smooth areas like clouds. Sixteen bits per color allow 256 steps between each 8-bit step or level, allowing for much greater changes without visible image problems.

A similar thing is happening in video cameras but 16 bits per color are more than most video systems can handle, higher quality video cameras provide recordings with 10 bits per color, still four steps between every 8-bit step – a big help in post production.

So how much camera and how much processing do you need? That depends on what you will use the stills or video for. If you are going to a movie screen in a big theater, you had better think about using high definition video at 1920 x 1080 pixels per frame and you will probably want to be compatible with current movie standards of 24 frames per second.

Shooting 24 frames requires that you pay attention to camera pan and tilt rates or you will end up with blurry or jumpy clips, depending on your shutter speed. Most 24 frame video is shot at 1/48 sec shutter speed, just like film cameras, to achieve a good compromise between motion blur and motion “judder” the effect caused by moving the camera across a background or having an object jump across the frame in visible steps.

If you are planning to show your movies on a smaller screen, you might want to use the lower resolution high definition standard of 1280 x 720 pixels at up to 60 frames per second. The 60 frame version gives you superb motion reproduction and allows excellent slow motion shooting, at the expense of bigger files and longer transfer times from the camera.

If your main interest is in web tv, then your may not want to bother with HD at all. You can get faster load times and adequate results with cheaper processing hardware (computer) and software (editing program) if you stick to standard definition video (20th century television).

And don’t forget that all of your images are now on digital media so you can’t go back to an original tape if your disk drive crashes. So make backup copies of all of your computer data, especially your images and video clips.


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