What I learned from Gollywop -- and what I wonder

Started Mar 26, 2013 | Discussions thread
bowportes
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Re: What I learned from Gollywop -- and what I wonder
In reply to gollywop, Mar 27, 2013

gollywop wrote:

Macx wrote:

gollywop wrote:

bowportes wrote:

As an old fart of a photographer, I thought I knew all about exposure -- you know, aperture, shutter-speed, and ISO. The point was to nail the proper exposure as given by the camera. Behaving like I had ektachrome loaded in a digital camera, I rarely over- or under-exposed unless I had a situation of backlighting or snow. The Panny G-series cameras, by shifting the color of the histogram to yellow (caution) if I used the thumb-wheel to increase/lesson exposure, encouraged me to keep it white -- right where the camera automatically exposes.

This may be fine general practice for JPEG shooters, but it turns out it was wrong for capturing raw.

Gollywop's recent post encouraged me to think instead of maximizing the sensor's exposure to light. Rather than accepting the camera's exposure, I should overexpose images just (but not quite) to the point of clipping highlights at base ISO (ETTR). The histogram may go yellow and the image may appear too light in the viewfinder, but as long as the right side of the histogram has not reached the right edge of its axis, go ahead and overexpose. My raw-processed image will be better for it, in spite of the fact that it doesn't look as good in the EVF at +2/3 exposure as when it's not set to overexpose. Watching the histogram (or blinkies on an Olympus) is your key for how far to amplify exposure.

texinwien's post just under your OP pretty much answers your questions on the button. Now all I have to do is get you to not use the term over-expose as you have above

Over-exposre is when you blow out the sensor at base ISO. You can be excused for a confusion on this score, because in my post Exposure vs. Brightening, I used the term over-saturate for this. But it was agreed by many that the term saturation should be reserved for its meaning in describing color intensity. Thus, in my revision I am reclaiming the term over-exposure to mean the situation when so much light falls on the sensor that some photosites (sensels) are gifted with more electrons than they can hold -- blown, in the vernacular.

So rather than "I should overexpose images just (but not quite) to the point of clipping highlights at base ISO (ETTR)" you would think "I should expose at base ISO to just below the point where raw clipping occurs, ETTR." This is not over-exposure, it's just plain ETTR.

Something that's not as clear to me though. If ISO is at base (160 for most Pannys and 200 for Olympus), the lens is at maximum aperture, and shutter-speed can't be set slower, but the histogram still sits right in the middle -- not overexposed at all -- if I understand correctly, I might get some improvement in image quality by raising the ISO to 400 or 800 in order to (overexpose -> brighten) the image, as long as I'm careful not to (overexpose to the point where I'm clipping highlights -> overexpose). I'd like confirmation that this is correct.

Again here. In the above, I've altered the verbiage that has been bold-faced. The boldface regular is the original text. The boldface italics is my suggested replacement. In the second change, note that overexposure to the point of clipping is redundant.

Don't use "brighten" in this sense, though. You're raising ISO to 400 or 800 to reduce read noise and maximise available camera dynamic range, NOT because it brightens the raw file (which it can't) nor because of what it does to final image after the raw file has been developed, which would be unwanted.

The G5 appears to be a very slightly semi-ISOless camera. Read noise does fall up to 800 or without commensurate loss in DR -- but the read noise is pretty low across the board. So it would appear you could exploit some ISO increases with relative impunity if they otherwise worked to your advantage when you are unable to ETTR.

Another situation that I've commonly encountered in the past is desiring to have the lens wide open in bright daylight. This typically means ISO is at 160 (base), my F1.8 or 2.8 lens is wide open, and shutter speed is as fast as my G5 can take it. In the past, the EVF still sometimes indicated this gave too much light, so I was compelled to reduce my aperture since ISO couldn't be lowered and SS couldn't be increased, and my goal was to achieve proper (exposure -> brightness) for my raw file. But now, if I understand the Gollywop thread correctly, I should be pleased with the (overexposure -> exposure) and leave the aperture wide open, as long as (it doesn't clip highlights -> highlights aren't clipped).

Again, just sayin'.

And again, it's meaningless to use "brightness" to describe a raw file. Your final image may be bright or not, but the raw file isn't, and final image brightness has nothing to do with your camera settings.

I'm in full agreement with everything else

You are indeed correct.  I have misspoken.  One can brighten the raw file (in the sense of increasing its data values) but brightness refers properly only the a final image.  So above with the (exposure -> brightness) it ought either be "brightness of my final image" or "brightening of my raw file" depending upon which he really had in mind.

Well, isn't it kind of meaningless to talk about the "brightness" of any file, including a JPEG? All of them are simply digital containers with some mix of data that have to be interpreted by software to generate an image, however bright the final visual interpretation might be. If I open a raw file in LR, it gets interpreted and presented as an image of greater or lesser brightness just like a JPEG would. The same is true for opening JPEG data. It's really only once it is printed on paper that the physical image has a certain level of brightness/luminance.

You've really got an uphill struggle for this purity of language thing. Even those of us who have started to get the point use the language incorrectly. Beyond us, you will have to battle:

Adobe: Lightroom uses "Exposure" for its brightness slider

Olympus: Their Brightness slider in Olympus Viewer 2 is called "exposure compensation"

Etc. Etc.

What is more, all of my raw developers use in-camera settings to determine how brightly to first display the image. So if I over-expose the image (over-brighten in your sense) by shifting the camera's exposure compensation wheel, then they appear that way in live-view, and also in the raw processor when the file is first loaded (unless I set the raw editor to display them differently). In each of these settings, the use of "exposure" for "luminance" in photography is so entrenched that it almost makes me wonder whether you should concede the term "exposure" to communicate brightness, which is how people think of it, and then find another term to signify sensor charge/load, which most people don't think of at all.

Anyway, you've got a great communication challenge ahead to straighten this out, but you've taught me a fair bit, so I'm rooting for you.

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