False Colour

Methods of monitoring exposure and reducing noise on the Sony PXW-FS7.

CineEI Function

The camera will always record at its native ISO when in CineEI mode, you can however change the effective ISO using the exposure index (this will not change the recording ISO) similar to how a a camera operator using film would have a fixed ISO film stock and would choose to rate their light meter differently to treat the film differently (e.g. pushing or pulling the film)

The EI function allows you to rate the camera at different ISOs to alter the midpoint of your dynamic range. This can be beneficial in post-production as you can reduce signal to noise when using a lower EI.

Changing the EI only changes the brightness of the MLUT, so when you see that it is darker at 1000EI (1 stop down) you should increase the aperture by 1 stop to compensate to get the same brightness level as a conventional range. Due to the camera still recording at 2000 ISO you will be recording 1 stop brighter, when this is taken into post the image will be brighter you will bring down your gain levels and doing this will also reduce noise. The catch is that because the aperture is open a stop higher you will start to eat into your over exposure range, so highlights might start to clip in lighter scenes, but in darker scenes you will be able to see further into the shadows.

Exposure Tools

Under the VF section of the camera settings there are some exposure tools available:

• Zebra
• Waveform monitor
• Histograms

Zebras

In CineEI mode the zebras will measure the view finder image and the waveform and histograms will measure SDI2 signals. So, if a LUT is enabled in the viewfinder it will measure the LUT and if there aren’t any enabled it will measure the chosen sLog.

Zebras measure the signal levels and when they reach a set level the areas that are hitting the selected signal point will display hatching, there are two types of zebra: 1 and 2.

Zebra 1 is set to exposure levels and will trigger when an image hits that point, an aperture range can be set so if the zebra is set to 70% with 10% aperture, the zebra will indicate that the exposure is between65% and 75%.

Zebra 2 is an over exposure indicator that turns is triggered when something hits or exceeds the selected over exposure point.

Waveform Monitor

The bottom of the wave form represents 0% (Black) and the top represents 109% (peak exposure), skin tones and mid ranges should tend to sit at around 60%. If the data on the histogram all sits below the 50% mark the image is under exposed, and if it all sits above 50% it will be overexposed. The wave form should be spread out across the graph ideally with nothing hitting the top or bottom.

Histogram

The histogram measures the exposure range from left (Black) to Right (white) the height of the peak corresponds to the amount of the image that is exposed at that level. For a good exposure on images, you want a spread from black to white with a peak in the middle of the video, if the data is bunched up on ether end the image is incorrectly exposed.

False colour

False colour techniques enable you to substitute the colours in your images based on the level of exposure, they can be applied as MLUTs when filming to make sure that the exposure is set properly so there is a full dynamic range to work with in post-production. False colour can also be used during the grading process to act as a guide for the exposure.

To test the effect of false colour I have created an MLUT that can be loaded into the PXW-FS7 to display on the monitor or viewfinder so that exposure can be monitored whilst filming. To make this easier to understand I have also created guide which relates each colour to the level of exposure that they correspond to.