Smart_Photography_-_September_2019

Bit depth

This is very similar to the bit depth of

still cameras. You may recall for still

images JPEG format gives a bit depth of

8 bits (for each colour channel). Raw

format allows 12 or even 14 bits. More

bits simply mean that there are more

levels available for better quality. This

also allows more leeway when editing.

Till recently ILCs offered only 8 bit

recording. However, some advanced ILCs

are now offering log output (more of that

in a moment) which allows for better

post production called colour grading.

The latter requires more bit depth for

good results just like in still images.

Consequently, many ILCs are now

offering 10 bit depth in recording.

Log output

If you see the data sheets of current

generation ILCs you will come across

terms like N-Log, C-Log, S-Log, V-Log,

etc. What do these mean? To understand

that, first let us see how the input vs

output curve looks like (Picture 2) for

a digital sensor. This as you can see is

linear, that is a straight line, and the

slope of the line is called ‘Gamma’. A

linear relation means that within limits

the output (electric signal) increases

as the input (light intensity) increases,

proportionately. However, such a

relationship allocates less digitising

levels to darker tones and does not

preserve highlight and shadow details

well.

So, the input – output relationship is

modified using a logarithmic (short form

is log) function (Picture 3). What is being

done here is that lower and middle parts

for the linear graph are pushed upwards

(see the steep rise on the left side of the

curve) where more levels are available.

The result is that both highlight and

shadows are preserved, and thus you

will record a greater brightness range.

This process also renders exposure

differences in a way similar to what we

humans perceive. However, the image

will now look a bit flat (or washed out)

with low contrast (Pictures 4 and 5).

This can be easily dealt with, and the

output can be tailored for different

results during the colour grading. One

small technical point; log output is not

raw data as it is processed.

Now, what are those letters N, C, S, etc.?

These are just implementations of the

log function by different manufacturers.

They are in principle the same, but the

implementation will be different for each

manufacturer as the algorithms might

have been optimised to fully utilise

the dynamic range of their respective

sensors.

Audio

A still photograph needs no sound.

However, even the simplest home

video of a birthday party without the

mandatory singing will ‘sound hollow’

(pun intended)! All ILCs have a provision

to record sound through an in-built

microphone (or mic for short) with some

menu settings available to control the

sound input. Just like video, audio is also

recorded with a codec, the most common

ones being MP3, AAC, etc.

File formats: Still photographs are

stored in several file formats like JPEG,

TIFF, etc. Likewise, video files too

can be recorded in different formats.

However, the process here is a little more

Number of levels allocated by the camera

Picture 2: A linear relationship graph

Number of levels allocated by the camera

Picture 3: A log curve

http://www.smartphotography.in September 2019 | Smart Photography | 95