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Old Oct 24, 2006, 6:54 AM   #1
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Hi - new post, and I think a new question, but first some background: I have a Ricoh R4 camera (got it for the very compact size, fits in pockets very nicely) which takes visually noisy shots at higher ISO settings, particuarly above ISO 200. Iso 64 is relative good quality, and although the shot will be darker for a given exposure, this can be corrected by adjusting the brightness in an image editing program. This increases also the noise, but seems to have less net noise than taking at a high ISO to begin with. Does this method have hidden costs, other than an extra step in processsing? I'm a new member here - sorry if this is in the wrong forum.
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Old Oct 24, 2006, 9:40 AM   #2
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The hidden costs are:

(1) washed out color - if you turn the brightness up too much.

(2) loss of detail -

If you set low ISO to take picture in dim lighting, the sensor may not pick up some detail in the scene. What the photo editing program does is to increase the brightness of what is in already the picture - whatever is missed because it is too dim cannot be created or "recovered" by increasing the brightness afterwards.

Increasing the ISO does capture more light and more detail of the scene. However, as you said, if the high ISO performance is poor in your camera, you may not get much more detail from it. This is because either there is too much noise (which appears as speckles and grains that may blur the detail), or there is too much in-camera noise-reduction (which reduces noise while blurring the picture).

If you find that your camera's built-in noise reduction is not too severe (ie. your pictures at high ISO comes out grainy rather than blurry), you may take pictures at high ISO, and use a noise reduction program or plugin to reduce the noise level afterwards. These programs sometimes do a better job than the camera's built-in system, and you can manually change the settings to optimize the result.

Another tipon photo editing: use "gamma correction" instead of "brightness" - gamma correction changes several parameters of the pictures to improve brightness, color and contrast at the same time. This may give a less washed-out look.
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Old Oct 24, 2006, 11:59 AM   #3
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A correctly exposed (or even slightly overexposed) image usually has the lowest noise when shooting at higher ISO speeds. Even a slightly underexposed image can cause a relatively high increase in noise levels.

As a general rule, if you underexpose your photos and brighten them later, you'll get just as much or more noise (usually more) as you would by using a higher ISO speed to begin with, if your aperture and shutter speed are the same.

IOW, if you use ISO 100, f/2.8 and 1/60 second and get a photo that is one stop underexposed, versus a correctly exposed photo using ISO 200, f/2.8 and 1/60 second, then noise will be just as high or higher after you brighten the ISO 100 image to match it.

In addition, you'll reduce the dynamic range in the image using this technique. You will get the best dynamic range from an image that's exposed with the histogram to the right. Using "Push Processing' (deliberately underexposing to simulate higher ISO speeds and brightening later), will substantially reduce an Image's dynamic range with Digital.

Depending on the camera model, you can sometimes get good results this way anyway if you have a camera model that is using a lot of noise reduction in the image processing pipeline.

That's because some models deliberately smooth out the noise at higher ISO speeds, resulting in loss of detail. So, you can sometimes get more detail brightening an underexposed image shot at lower ISO speeds instead (with higher noise levels versus the camera produced image after you brighten it). But, sometimes a bit more noise is preferrable to the camera's noise reduction algorithms, if you have a model that deliberately smooths/softens an image when shooting at higher ISO speeds.

The easiest way to push process is to use Exposure Compensation. For example, if you use a -1 EV setting with Exposure Compensation at ISO 100, you will get the same shutter speeds as you would using ISO 200 in most modes shooting in lower light (because the camera will already be using a wide open aperture in low light, so it uses faster shutter speeds to darken the image). Then, brighten the image later using your favorite editor. The "Fill Light" feature you'll find in some editors (for example, Picasa) is good for this purpose.

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Old Oct 25, 2006, 6:05 AM   #4
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I learned about this the hard way, by taking pictures at a friend's wedding reception with a Kodak CX4200 a few years ago. The view on the LCD looked fine after each shot, but the pictures were almost all way too dark. (The spirit was willing, but the flash was weak.) I could lighten them on the computer and increase the contrast so they looked halfway normal in terms of exposure, but they were noisy as heck.
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