Architect1776 Loc: In my mind

Nicholas DeSciose

ISO - Is not noise

Nicholas DeSciose

And interesting aside. The majority of the motion picture community and motion picture technical publications still use ASA

Dikdik Loc: Winnipeg, Canada

Call it what you want... ESTHP? the electronic 'stuff' that happens to photographs with higher ISO values.

Dik

amfoto1 Loc: San Jose, Calif. USA

This is correct.

Digital cameras actually only have a single "base" ISO and everything else is derived from that. The base ISO in any digital is the lowest setting within their "normal" or "native" range of ISOs... the lowest setting that can be made without "expanding ISO". In most cases today, it's ISO 100.... A few cameras use ISO 64. In the past a few have used ISO 200 and, I dunno, maybe some still do.

It's important to note that most digital cameras have two types of amplification. It's an oversimplification, but call them "hardware" and "software" amplification.

Hardware amplification is the "native" range of the camera (the "un-expanded" range). The camera has circuitry with components that amplify the image, for any ISO other than the "base".

Software amplification is the "expanded" ISO found on many (most?) cameras... usually these are ultra high ISOs (25600, 32000.... even 51200, 102400 or higher... much, much higher in some cases). Some camera also have a lower "expanded" ISO such as 50 or 32.

Images that are software amplified are actually shot at a lower ISO (probably the highest possible within the native range)... essentially under-exposed... and then "tweaked" by the camera's software to appear as if they were shot at the higher "expanded" ISO that was selected by the user. In a sense, with the "expanded" ISOs you are further amplifying an image that was already hardware amplified! This is why the image quality tends to drop off dramatically with the expanded ISOs.

Another way of looking at this.... "expanded" ISOs are much like you shot the image at the highest possible "native range" ISO, and then in post-processing you used the exposure adjustments to brighten the image. This always greatly increases the appearance of noise in images.

Personally, my rule of thumb is to keep to the native range of any camera... To NOT use the expanded ISOs. About the only exception I make is if I plan to do a black & white conversion of the image. Image noise generally isn't a problem in B&W (or any other type of monochrome conversion).

Everyone talks about the increase of "noise" appearing in images at higher ISOs. But what many people overlook is that higher ISOs also cost you dynamic range and resolution. Sometime do a series of test shots with your camera at various ISOs. If you do so carefully using the exact same subject, only changing the ISO from image to image and offsetting that by changes to the shutter speed, you'll find that the higher the ISO, the smaller the file size. If you look at the histogram of the images, you'll also notice the higher the ISO, the narrower the range of tonalities that graph will display. Because of this, it's not uncommon for higher ISO images to need their black point and white points adjusted, for contrast to be added. But it also represents a drop in resolution (which can be made worse by applying too much noise reduction, which removes fine detail from images).

On the cameras that offer it, a lower expanded ISO is also software derived and will have some image quality loss. I'd really like a digital camera that had ultra low ISOs available... ISO 25, 16, 12, 8 and maybe even lower would be useful at times. However, I have never seen this done digitally and have been told there's just too much loss of IQ to make it worthwhile (a higher "base" ISO along with a Neutral Density filter can do the same job better).

So, yes, in a sense all ISOs are "fake". They're all derived, one way or another, from a single ISO. Over the last 20, 25 years, digital cameras have gotten better and better at this... They now offer usable ISOs that are far higher than we ever dreamed would be possible when we were shooting film.

But it's important to know HOW the higher ISOs are being derived.

Best thing you can do is make a series of test shots with your camera, to learn how it handles various ISOs. Try both RAW (conversion and noise reduction in post-processing) and JPEG (in-camera conversion and NR)... Also try different types and methods of noise reduction. Learn what works and what doesn't.

In my opinion, the biggest mistake people make is evaluating their images for things like noise at waaaaaayyy too high magnification. Viewing an image from a 24MP camera "at 100%" on the typical computer monitor is much like making a 3.5 FOOT by 5 FOOT print (approx. 1 meter by 1.5 meter, for our metric friends), and then viewing it from only 18 or 20" away. OF COURSE it looks like crap! Are you planning to print it that large? And, even if you do, will you ever view it from so close?

Everyone does it. Looks at their images "at 100%". It's even common on photo forums for "100% crops" to be used in discussions.

BACK OFF... while it can be handy to highly magnify an image for retouching work, it makes little sense to evaluate many of their aspects so highly magnified. Zoom to a lower magnification that's closer to the size the image will actually be used... whatever that may be. With a 24MP camera, even 50% is like a very large 20x30" print. Even 25% is similar to a 16x20" print. (All this assumes no cropping and that the user's monitor is set to it's native resolution around 100 pixels per inch). Very often, by the time an image has sized for the "real world" purpose, any noise (or even minor focus error, etc.) will no longer be noticeable. So the only person to ever see the noise (or whatever) is the photographer them self, while they're working with the original image file.

Dikdik Loc: Winnipeg, Canada

Great write up...

Dik

drobvit Loc: Southern NV

I've seen a few of their vids. They do act like the ultimate authority in photography. Yes, everyone is entitled to their opinion but they strike me as being a bit (a lot) arrogant. You can glean useful info but I find them to be off-putting. Not my cup of java...

AndyH Loc: Massachusetts and New Hampshire

Important points, Alan. Everyone should run these simple tests.

Andy

Blair Shaw Jr Loc: Dunnellon,Florida

Anything electronic having to do sensory or light output will vary over time with continued use. Even a light bulb will lose 40% of it's illumination after only 1/3 of it's life and the average human will not detect the loss at first......only by comparisons with a newer lamp will they discover the shortage.

ISO , Guide Numbers ,Calibrated-Standards are all recommended starting points and Not Written in Stone for the seasoned artist. He or she will adjust tonal qualities to their individual standards and become familiar with any given camera solely on it's individual performance. It isn't rocket science.........don't sleep with other cameras...hahaha

cdayton

I have a tourist world map from NZ where south is the top.

Longshadow Loc: Audubon, PA, United States

Incandescent or LED or both?
I'd love to see the article on that!
Can you post a link?

amfoto1 Loc: San Jose, Calif. USA

Quite true!

And that's exactly why I regularly calibrate the monitor I use for image post-processing. It's maybe 6 or 7 years old now.... And like most monitors when new it was waaaaaaayyy too bright to work with photos (which would have caused me to adjust my images way too dark). When it was new and tested with my Spyder calibration device, I had to turn the brightness down to "20". I don't know if that's a percentage or if it's just an arbitrary scale, it really doesn't matter. What's important is that now, after 6 or 7 years use, when I calibrate each month I'm finding the correct brightness setting is a little over "50". That's the monitor aging and losing brightness (kinda like me... although I'm also losing hair, muscle tone and other things ).

Monitor calibration also insures that color rendition is as accurate as possible. But the first thing it does is set a correct brightness.

Architect1776 Loc: In my mind

Longshadow Loc: Audubon, PA, United States

Love it.

xt2 Loc: British Columbia, Canada

On my cameras, ISO seems to be real.

Cheers!