Wednesday, April 9, 2014, 3 mins 6 secs

Understanding an Image

Design@Think201 in Design Photography

Some questions that always arise in amateur photographer mind, in which mode to shoot? RAW or JPEG? What is the difference between 16-bit and 8-bit images? This blog will clarify all your doubts.

An image is a combination of pixels which are displayed on screen. Pixels can be of various colours. According to optical physics there are three primary colours i.e, Red, Green and Blue . Any other colour is a combination of these three colours only. But if we apply the laws of combination then we can create only 8 colours out of these 3 colours, and those are :

1) Red

2) Green

3) Blue

4) R+G+B = white

5) R+G=Yellow

6) R+B=Magenta

7) G+B=Cyan

In the absence of all the colours we can create Black.
Other than RGB there is one more colour system called CMYK, Where Cyan, Magenta, Yellow and Black are treated as primary colours.

cmyk-rgb

Ever wondered how we are able to see millions of colours on screen while the primary colours can create only 8 colours? Well, it’s because we use multiple shades of a single colour. We mix multiple shades of these primary colours and a new colour is formed and this is where the concept of 8-bit and 16-bit comes.

In an 8-bit image each primary colour can be represented by 8-bit binary number. Each of the 8 bit binary numbers represents a specific shade of that colour.
So total number of shades of a single colour in an image is 2^8 = 256

And total number of colours we can see is,

256*256*256 = 16777216

Similarly in a 16 bit image each colour can be represented by a 16bit binary number, resulting 2^16 = 65536 shades of a single colour.

Hence total number of colours we can see is,

65536*65536*65536 = 281474976710656

Isn’t it amazing that using just 3 colours we can see billions of colours!

But human eye cannot process these many of colours. We have limited capacity of differentiating colours. If you place a 16 bit colour image beside an 8-bit image, you can’t identify which one is 16 bit and which one is 8 bit. But a 16-bit image requires more memory space than 8-bit images as each pixel uses more memory.

So the question comes, what is the need of taking 16-bit pictures?
Photographers are always advised to take pictures in RAW mode, which is a 16-bit image, uncompressed and straight from the camera sensor .The main advantage of 16-bit images is Flexibility over post processing/ editing. As a 16 bit image contains more information than an 8-bit image (jpg) less information is lost during a post processing and the changes can be rolled back without any damage to the details.

For example if there is a gradient portion in an image and we change the levels of that image. But for some reason we need to roll back that process for further processing.
In such situations in case of an 8 bit image, when you re-change the levels graph, the image cant regain its previous state but in case of 16 bit image it is possible, because it contains more numbers of shades(which guarantees smooth transition of colours) .
RAW images are less sharp than JPEG images as they are raw information from the camera sensor .It takes more time to be saved in memory because it’s a large file. Where as in case of JPEG, the sensor information is processed and sharpened within the building camera software, which is of less memory size and hence gets saved quickly.

The sole purpose of using 16 bit images is ‘Flexibility’ in post processing in Photoshop or other processing tools and which is an essential part in photography. An 8-bit guarantees optimal use of space while 16 bit image guarantees flexibility over processing. So, it should be used according to purpose.

Design@Think201

Design@Think201