Optimum Color Temp

[Daniel Browning]

Originally Posted by Noah Yuan-Vogel

It seems like maybe we are talking about some of these issues in different terms.

Yes.

Originally Posted by Noah Yuan-Vogel

I wasn't assuming just overexposing the image as iso increased, I meant assuming exposure was compensated.

I see.

Originally Posted by Noah Yuan-Vogel

In that case, can you explain further how your explanation of what happens in a situation where iso is increased and exposure is compensated in terms of dynamic range and noise relative to the original situation (lower iso and more light)?

Sure. The effect is different for the RED ONE (metadata ISO) than it is for 5D2 (in-camera ISO):

• 5D2: If exposure is reduced by one stop and ISO increased by one stop to compensate (e.g. f/4 to f/5.6 *and* ISO 200 to ISO 400), then highlight headroom stays the same, noise gets worse in all zones (due to photon shot noise), but read-noise dominated zones, such as shadows, don't get that much worse (less than a stop worse). Brightness of the file, the image on the LCD, and post-production image stays the same.
• RED ONE: If exposure is reduced by one stop and ISO increased by one stop to compensate, highlight headroom increases one stop, noise gets worse in all zones (due to photon shot noise), and shadow detail decreases one stop (less signal no change in read noise). Brightness of the file goes down. image on the LCD stays the same. Post production image brightness stays the same.

Originally Posted by Noah Yuan-Vogel

Also, I am not following what you mean when you say sensitivity does not change when you increase hardware gain. If increasing iso from 100 to 3200 allows you to under expose by 5 stops and still get good exposure and not lose 5 stops of dynamic range, then how is that not increased sensitivity? Are you talking in terms of a photosite's reaction to a photon or something? Perhaps we are defining sensitivity differently?

I think it's a terms/definition problem as you guessed. Here are what the terms mean to me:

Exposure: intensity of light falling on the sensor.

This is a function of scene luminance, f-number, and shutter speed. Also filters, lens transmissivity, and perhaps other factors. I think this is the original and correct meaning of the word exposure.

Luminance: This is the brightness of the image. It is separate from exposure.

Sensitivity: Response to light.

This is how the sensor responds to light. If it requires 9 photons to cause 1 level change, that is lower sensitivity than a sensor that only requires 3 photons.

Read noise: All noises aside from photon shot noise.

This includes all temporal noises such as reset noise, thermal noise, flicker noise, RTS noise, and amp noise. At base ISO, this type of noise only affects the extreme shadows. The bright parts of the image are only affected by photon shot noise. The higher the ISO, the more exposure zones that it affects.

Here are some examples how these definitions affect the discussion:

In the RED ONE, when the ISO setting is changed from 320 to 640, it doesn't actually change the exposure, sensitivity, or read noise of the camera, it just instructs the post processing to increase the brightness and it also increases the brightness of the display monitor.

In the 5D2, when the ISO setting is changed from 200 to 400, it doesn't actually change the exposure or sensitivity of the camera, but it does decrease the read noise, and it does increase the brightness of the file, and it does increase the brightness of the display.

In the 5D2, when the ISO setting is changed from 200 to 400 and the exposure is decreased one stop (e.g. f/4 to f/5.6), it does change the exposure, does not change the sensitivity, it does decrease the read noise. The brightness of the file and display remains the same. Read-noise dominated zones, such as shadows, don't get a full stop worse.

Originally Posted by Noah Yuan-Vogel

Where did you get the information regarding RED's read noise not changing at other hardware gain levels?

I thought I read a post by Deanan DaSilva or Graeme Nattress where they tested the RED ONE with higher analog gain and found that the read noise was the same; however, I can't find it now, so I retract the statement.

Originally Posted by Noah Yuan-Vogel

Doesn't every digital camera decrease read noise with hardware gain increases?

No. It only seems to apply to certain pixel designs. Other pixel designs have the best of both worlds: low read noise *without* increasing gain. The Nikon D3X has a read noise of only 6 electrons at ISO 100, whereas the 5D2 has 23.5 electrons. The 5D2 has to sacrifice 2 stops of highlight headroom by setting ISO 400 in order to get read noise down to 6 electrons. Of course, the 5D2 can get all the way down to 2.5 electrons read noise at ISO 1600, where it can easily beat the D3X, but it would be much better if the 5D2 had 2.5 electrons read noise at ISO 100.

Even Canon cameras only improve up to ISO 1600. 3200 is hardware analog gain, but has no improvement in read noise.

Originally Posted by Noah Yuan-Vogel

Isnt it a shortcoming not to?

It's a design compromise. The 5D2 has a nice low read noise at high ISO, but at low ISO it's terrible. I'm sure they will figure it out in the future.

Originally Posted by Noah Yuan-Vogel

Given a circumstance where one is shooting in an environment where correct exposure occurs at iso1600, on the RED ONE you are stuck with a noisy image where most of your range is unused (maybe 9bits out of 12) and with the 5DMK2 you can achieve correct exposure (and use all 14bits in still raw mode) using hardware gain and lose much less shadow detail to noise, no?

First, the exposure (aperture & shutter) is the same on both cameras, so neither is "incorrect", per se. Second, the brightness is the same on both cameras as well (in the case of the RED ONE, the brightness is added to the display monitor and in post production instead of the in-camera file).

Third, the range of bits "used" is the same on both. As explained in the Noise, Dynamic Range, and Bit Depth section of Emil Martinec's essay, none of Canon's cameras suffer quantization error under any circumstances, even when pushing ISO 100 ten stops, so there is literally no benefit to the 14 bits at ISO 1600. In fact, at ISO 1600 you can replace the raw 14-bit Canon data with 10-bit data and lose absolutely no image information whatsoever. Take a look at this visual demonstration:

Canon 40D raw file compared from 14 bits to 7 bits

So essentially your comparison comes down to the fact that at ISO 1600, the 5D2 has less read noise than the RED ONE.

Originally Posted by Noah Yuan-Vogel

I recall seening video shot at iso 1600 on RED and the same scene on 5dMK2 at iso 1600 and the difference seems massively in favor of the hardware gain method of the 5DMK2

There are other cameras with hardware gain, such as the D2X, that can't hold a candle to the RED ONE. What matters is the read noise, and Canon is the king of random read noise.

I hope that helps clarify things.

[Wayne Avanson]

Originally Posted by Luis de la Cerda

After some shooting and testing and more shooting and more testing, this is my re-re-revised favorite picture style. It has nice contrast. It preserves shadow details quite nice. It avoids solarization due to oversaturation without being washed out. It has sharpness dialed all the way down to avoid haloing. Colors also look close to real life when a color temperature preset such as sunlight or tungsten is used. Try it, modify it, comment on it, upload it back modified... Your call. :)

Thanks Luis, going to have a play with that later. Looks, on the surface of it, quite natural and a little filmic. Migh be good for a little shoot I have planned for next week.

Cheers

Avey