Raw format

Ok, this is a contentuous argument here, and I'm confused, even after reading the various Websites on

what exactly is a raw format file from the camera. According to these Websites the raw file is the actual

data only determined by the ISO, and no other factor is involved, including exposure setting, such as

aperture, shutter speed and EV control. Is that really true? Because I don't see how the exposure values

have no effect on the captured raw image, or else they're really useless? And that we know they're not.

Second, I've read that color temperature and/or white balance has no determination of the raw image from

the camera, along with picture style. Yet, when I take a series of images through the settings, I get a set of

different raw format images across the settings, viewing the Canon .cr2 file with their image browser with

histograms, which are also different? So why if raw files are "original data", the raw files different? Every

user control seems to effect the raw image file from the camera.

Granted, digital sensors aren't film, but even film doesn't follow any of this premise where nothing but ISO

determines the captured image. Everything does including the film type. I'm still testing this and trying to

understand what the camera is doing, but what's being explained doesn't seem to be matching what I'm

getting from and seeing with the camera. And ok, it's a Canon 5D. Just my observations and help

appreciated, but not the same thread, "It is that way. Trust me." Do folks have the descriptions or

explanations from the camera companies, because I can find them on some of their Websites?

ps. I posted this here because it's a casual conversation, not unlike at a tavern, so it's in that vein, thinking

out loud over a good stout ale.

1.) "ccording to these Websites the raw file is the actual data only determined by the ISO,

and no other factor is involved, including exposure setting, such as aperture, shutter

speed and EV control. "

That is silly. Of course exposure controls play a part. Which websites?

2.) What you are seeing is because bundled in the raw file from your 5D is a bunch of

information (metadata) encoded by the camera that Canon's raw processing program is

utilizing. These are more or less processing suggestions or prompts to Canon's software.

3.)

As Ellis says, some of camera settings do still affect RAW files...particularly the aperture (which physically controls how much light reaches the sensors) and the shutter speed (which controls how long the light hits the sensors). Changing these will change the RAW file.

But the file is "RAW" because the camera doesn't apply most of the automatic adjustments that it normally uses for JPEGs...things like brightness/contrast adjustments and sharpening.

Sincerely,

Dave

Consider raw data to be analogous to exposed but undeveloped film. Neither is a viewable image. When you develop film you destroy the raw data. Digital development is non-destructive. The undeveloped film is already an emulsion which will characterize the image when you develop it. Digital raw is made up of all the things undeveloped film is contains, except the characterizing emulsion. It has the focus, exposure settings, and sensitivity.

The in-camera jpeg settings are "emulsions" applied after the fact of exposure. If you shoot raw you are putting off applying the emulsion to the data until after removing the data from the camera.

You see the effects of various camera settings when you open the RAW file, but these settings are only applied at the time of viewing or conversion. You are not actually seeing the RAW file itself. In Photoshop, you see any opened file as a PSD file, regardless of the source - RAW, TIFF, JPEG or other.

A RAW image is the data as it is taken from the sensor and stored in a file. The sensitivity (ISO) is about the only thing that affects the RAW file, since it is applied at the cell level before it is read by the image processor (CMOS) or as the data is dumped one row at a time (CCD). The RAW file does not even have color information - only intensity. The image processor only knows which color of the Bayer filter through which each cell was exposed. Data from each cell has a full 12 bits of data, which is reduced to 8 bits/channel if the image is saved in the camera as a JPEG or TIFF.

Exposure - i.e., shutter speed and aperture - do affect the image just as it would for film. The sensor cells register the total amount of light falling on their location. Likewise the effect of any filters applied to the lens (and sensor) are recorded.

Most of the parameters you set in the camera are tags used when the raw data is converted to another format (TIFF or JPEG), and for the thumbnail displayed on the LCD viewer. Some RAW interpretation programs, notably Adobe ACR, ignore most of these tags (tone, sharpening, etc), except for color temperature intent. Since the RAW file contains no color information, color temperature is applied only at the time of conversion, and can be changed without affecting the RAW file itself. You also have considerable latitude to adjust the exposure at this time, including overexposure (up to 4 stops).

"...including overexposure (up to 4 stops)."

Everything else is correct, but you don't gain up to 4 steps

latitude on the overexposure-side. Digital is very strikt here (much more than film). Once a sensor cell got maximum exposure it has reached the maximum 12bit value (after digitization). More exposure on this cell cannot generate any higher value after digitization. Highlights are now blown out. The more you overexpose, the more of your image will irrecoverably be blown out even if you use raw.

(To visualize this, imagine the sensor cell would be a little bucket

collecting photones...full is full...it cannot be overfilled).

Search PN for "expose to the right", I'm confident, that will dig up an in deepth discussion on this theme.

Rainer

Rainer,

With ACR, you can correct up to 2 stops of overexposure without loss, and up to 4 stops if at least one channel is correctly exposed. This is due to the conservative placement of exposure by most DSLR cameras. The histogram in ACR is derived from a 8-bit/channel map of the 12-bit RAW file, and reflects this conservative exposure. You will notice, when correcting exposure in ACR, that the histogram changes shape as the mode (peak) moves toward black, yet the white end tapers off smoothly. If you try this in Photoshop, the the shape does not change and the white end remains truncated, indicating that no useable data remains between the end of the histogram and the white point.

Thanks for the response, extremely helpful. It's still confusing that it doesn't apply color

temperature to the output raw file when I see different images in unconverted raw files taken

through the different white balance or picture styles with Canon image browser. But that's

for more tests. And I'll ask when I get there. Many thanks.

<p>Ok, I apologize, walking away from the computer for coffee I got to thinking. And that

as some have read my posts, is dangerous. But that said, if the raw file is just the intensity

in the output file, then it's the raw image display that converts it with the image metadata?

Then is it critical which raw display and converter you use? That's partly rhetorical, but,

following the image flow, it is the image converter that really matters.

<p>Observer 1: "Damn, won't that guy stop thinking out loud."<br>

Observer 2: "Yeah, just stop buying him ale."<br>

Observer 3: "No, take away his camera."<br>

Observer 4: "Hell, just ignore him and he'll stop all by himself. He'll just wander

away."<br>

Me: "Hey, I heard that. I'm leaving."<br>

Observers all: "Great. Bye. Don't let the logout hit you on the way."<br>

"Then is it critical which raw display and converter you use?"

Here is where the devil lurks in the details 8-)

After all the responses come in, the answer will be: download the free trials and try them out on the same raw file. Choose which seems right to you.

I've settled on Lightroom for raw conversion except for the raw files from my Canon G3. I prefer Breezebrowser Pro's linear conversion for those.

Some prefer a converter that produces an image that "looks just like what I see on the camera's lcd". This is usually one that came with the camera. I don't get it (why not shoot jpeg instead?). Some believe certain converters work best with certain camera's raw files because the manufacturer provided proprietary info about their raws unavailable to other converters. This may be true. I haven't seen evidence it is perceivable.

Edward,

I hope we agree, that one has to be quite desperate to try to correct a 4 stop overexposure.

The appended image shows from left to right correct exposure, one, two three and four stop overexposure with the required correction.

Even my reduced crops show the loss of detail on two stops and above.

Rainer<div></div>