MegaVision has an interesting approach to optimizing the signal-to-noise ratio of a capture. MegaVision makes a map of each and every pixel (we call this map a dark capture) and subtracts each pixel’s value above black, if you make a map and choose to implement its application.
When do you need to enable Dark Correct? When shadows start to look noisy. Noise shows up looking very much like grain in film. What causes noise? Several factors can cause noise, the most tangible factor is environmental, heat in the form of high ambient temperatures contributes to the noise in a digital capture. If the shooting conditions feature ambient temperatures, start looking carefully at the shadows and in necessary shoot a new Dark Correct.
Excessively high temperatures may yield noisier results. In reality, temperatures in the 80’s are not considered optimum for the operation of a computer and will therefore not be optimum for any digital camera. While we have generally become ambivalent about lofty operational temperatures for computer equipment, lower temperatures will extend the service life of any electronic component including computers. Most professional installations of digital cameras include a stable, cool ambient environment. Do not under estimate the value of an air conditioned studio. Be especially aware of the value of the optimally conditioned workspace if noise is an issue in your shooting environment.
To make a Dark Correct capture, pull down under Setup ahd choose Dark Correct and slide the cursor over to Capture. The software will display a prompt suggesting you should capture a shot for shutter speed. Shoot a picture, the camera will fire (the strobe won’t fire, it’s not supposed to) and the software will start making captures on the chip after the shutter has closed. We ask you to shoot the camera so the software will know what shutter speed you’ve chosen and make it’s compliment of captures (we make several captures and average the results) with the duration you selected. After the software is finished making the dark correct capture it will ask you where you want to save the capture. Navigate to the S2 Data folder within the PhotoShoot™ 2.0 folder and make the save there.
If choosing a shutter speed makes you think you could make more than one Dark Capture, you’re right. When shooting, you should evaluate each session for capture quality and make a new Dark Capture if low valued noise if objectionable. You could choose to replace the existing Dark Capture or you could change the name and store in addition to the standard Dark Capture. Why would you do this? Since longer shutter speeds capture more dark current noise, dark correct removes more dark current noise from longer shutter speeds than short shutter speeds. Could you use a longer speed dark capture for a shorter shutter speed photograph? Yes. You could make several shutter speed variable Dark Captures, store all of them in the S2 Data folder and choose from the flight of Dark Captures the capture that is the most noise free. You could also simply replace the existing Dark Capture with a longer speed Dark Capture by choosing Replace when the save prompt comes up, then go back to the capture speed you’re interested in shooting with. The value of keeping only one Dark Correct capture is you’ll limit the number of Dark Captures and potential of shooting with the wrong Dark Correct. You’ll also avoid using an invalid Dark Correct capture because of any changes in environment between the Dark Correct capture and the actual shoot.
When noise does show up in a capture you should be aware of it. You should be checking low values as a matter of course before saving any image or session. Close inspection of low values; for general placement of important reflectances and verification of adequate transition of tone is mandatory. This is where you will notice noise. Do not fall into slipshod technique by failing to evaluate the fit of your image to your intended target. When you do see noise and it cannot be temperature related, it will fall into two general possibilities: 1. An overaggressive (due to underexposure) Tone Correct in the shadow portion of the curve, and 2, a lengthy shutter speed (consider a Dark Capture at a longer speed than you’re shooting.
Tone Correct can add noise to a low value if you’re under lit and you’re using an aggressive curve to open up the low values. The display of noise is a physical reminder to light your way to better images, rather than wiggling software. Evaluate the shadow end of the Tone Correct curve. If it starts essentially straight up from the shadow on its way to the highlight corner, you may want to add some fill or increase the density range a bit so you can reduce the aggressiveness of the curve and thereby reduce the noise.