press:
Gamma curves for Sony’s F900/3 HD camera(II)

In this article we test the five curves developped by Digital Praxis for Sony’s F-900 camera, based on Cineon’s logarithmic system using CVOFile editor.

The main tools in the study of the curves were the grey card as well as the still life as can be seen in the images.



In this grey card we marked the value of grey in order to find its position in each curve.



In the image we can see the values for light shown in f-stops in relation to 18% medium grey.

Curve 1 Cin Log

This curve is a transcript of the standard Cineon curve, with some white clipping occuring given that the curve cuts at 106%. It has a black point adjusted to the standard Cineon profile, a profile that requires some degree of correction for colours and blacks in post-production as well as some correction in the mid-tones.





In the curve on the left we can see the values for greys; on the right there is a closer look at the shadow areas with value indicators.


In the monitor view of the grey card we can see how the gamma curve raises the blacks above the usual value as well as increasing the range in high lights. In general the image is softer than usual. We can see how the camera’s sensibility hardly changes with this curve. The curve’s latitude provides close to 9 f-stops, with a contrast ratio of 500:1. This is particularly notorious in high lights, achieving over three more f–stops above average density, which causes it to lose detail very softly.



Standard 4 grey scale


Cin Log curve

We can see in the image from the grey card how the blacks get darker and we attain more detail in the whites.


Standard 4 grey scale


Cin Log 1 curve

In the still life image we can see how in fact the washed out image contains details in the shadow and allows for more intense whites.



Standard 4 T 5.6 1/3 Grey 18 45%


Cin Log Curve T 5.6 1/3 Grey 18 45%


Original frame


Colour graded frame

After colour grading we can see how the curve maintains the detail in high-lights and shadows. Compare the level of detail of the lemons in this curve to the one of the Standard curve.



Curve 2 Cin Log 709

In this curve the shadow area in Cin Log has been replaced by the one that adjusts to the Rec. 709 Video Standard, which requires less work in post-production although mid-tones need to be adjusted. White clipping may occur in this curve, just as in the Cin Log.



In the graph we can see how the black in the curve has been adjusted to the Rec 709 norm.



Standard 4 Grey Card


Cin Log 709 Curve

Here we see how the blacks are darker with less detail while maintaining the ability to capture detail in the high lights.



Standard 4 Grey Card


Cin log 709 curve 2


Standard 4 T 5.6 1/3 Grey 18 45%


Cin Log 709 Curve T 5.6 1/3 Grey 18 45%

In the still life image we can see an improvement in the capture of high lights ( the lemons and the jug ) whereas the blacks have more density and are closer to the standard.


Original frame


Colour graded frame



Cin Log Chan Curve 3

The curve is based on Cin Log, with the black point brought down slightly but not as much as with curve 2
(Cin Log 709).



Close-up of shadow area. We see how the black point are half-way between those of curves 1 and 2.

In the wave monitor we can see how the level of whites remains the same while the level of detail in the blacks rises, although not as much as with curve 1.



Standard 4 grey scale


Cin Log Chan Curve


Standard 4 grey scale


Cin Log Chan Curve 3


Standard 4 T 5.6 1/3 Grey 18 45%


Cin Log Chan Curve T 5.6 1/3 Grey 18 45%


Original frame


Colour graded frame


En grafico podemos ver comparadas las tres curvas.





DPcin709-98% Curve 4

This curve is very similar to curve 2 (Cin Log 709) with the white clipped at 100% for 600% inputs.





In the graph on the left we can see the values for the greys and on the right we can see in more detail the area of shadows with the corresponding values.


Standard 4 grey scale


DPcin709-98% curve 4


Standard 4 grey scale


DPcin709-98% curve 4

Standard 4 T 5.6 1/3 Grey 18 45%


DPcin709-98% Curve 4 T 5.6 1/3 Grey 18 45%


Original frame


Colour graded frame



DPcinLog-98% curve 5

This curve is a perfect translation of the logarithmic cineon curve, except with a 0 value for the black point. This curve requires a lot of work in postproduction but delivers the biggest range of latitude in images with high contrast, without white clipping or compressing the blacks. Given the nature of the curve its possible that it offers an image with more values than those the HDcam system at 8bits can record; that’s why digital praxis recommends using a VTR recorder without compression, or S.Two D.Mag disc recorders.






In the graph on the left we can see the values of grey on the curve and on the right a close-up of the shadow area with referenced values.


Standard 4 grey scale


Curve 7D25L4VA44A


Standard 4 grey scale


DPcinLog-98% curve 5


Standard 4 T 5.6 1/3 Grey 18 45%


DPcinLog-98% Curve 5 T 5.6 1/3 Grey 18 45%


Original frame


Colour graded frame



In this graph we can see the comparison between the shadow area in curves 4 and 5

In the following graph we can see the comparison between the generic curves and the Standard Rec 709 curve