Photography Step By Step

Sensors from your digital camera consists of millions of pixels with photodiodes which convert the energy from the light (actually from the incoming phototns) into an electrical charge. That electrical charge is then converted to a voltage which is amplified to a higher level so that it can be further processed by the ADC (Analog to Digital Converter). In accordance with the voltage value, the ADC classifies it into a number of discrete levels of brightness and assigns each level a binary label (a number in binary code, consisting of 0 and 1). The ADCs are classified by the number bits that this labels are formed of. So a one bit ADC will classify the voltage as either 0 (black) or 1 (white). A two bit ADC would categorize it into four (2^2) groups (black-00; white-11; and two levels in between-01 and 10). Most consumer digital cameras use 8 bit ADCs, allowing up to 256 (2^8) distinct values for the brightness of a single pixel.

The minimum resolution (bit rate) of an ADC is determined by the dynamic range (accuracy) of the sensor. For example if the dynamic range of the sensor is 1000:1 (or 60dB) the ADC must be at least 10 bits which is 2^10 = 1024 discrete levels. This will avoid loss of information. Theoretically a 10 bit ADC is the perfect fit for this dynamic range (1000:1), a 12 or 14 bit ADC will not generate additional tonal information other than noise. However, in practice it makes sense to overspecify the ADC to 12 bits to allow for some margin of error on the ADC.  It is also useful to have extra bits available to minimize posterization or banding when applying the tonal curve to the linear data.
Often, marketing material advertises the bit rate of the ADC to suggest the digital camera or scanner is able to output images with a high dynamic and tonal range. From the above it is easy to understand that this is only true if the sensor itself has sufficient dynamic range. The tonal range and dynamic range can never be larger than the dynamic range of the sensor.
Digital SLR cameras have sensors with a higher dynamic range and are usually equipped with 10 or 12 bit ADCs. Normally such cameras offer the option to save the 10 or 12 bits of data per pixel in RAW because JPEG only allows 8 bits of data per channel.

Digital cameras have an ISO rating indicating their level of sensitivity to light. The normal setting for most cameras is ISO 100, although some go as low as ISO 50. The sensitivities can be increased to 200, 400, 800, or even 3,200. High-end digital SLRs also allow some intermediary values. When increasing the sensitivity, the output of the sensor is amplified, so less light is needed. Unfortunately the undesired noise is also amplified. This creates more grainy pictures, just like in conventional photography, but because of different reasons. It is like you will turn up the volume of a radio with bad reception. This will not only amplify the desired transmission but also the undesired noises. Lately a lot of improvements has been done in sensor technology to reduce the noise level at higher ISOs, especially on higher-end cameras.

Here is an example of how ISO level influence the final image:

So your question may be: why should I use higher ISO level if it adds so much noise in the picture? The answer is very simple. A photography with some noise in it is preferred to a blurry one. When you press the button to take the picture, a mechanism in the camera opens and expose the sensor to light for an amount of time (it is called exposure time). The lower the light level is, the greater the exposure time will be. If you are taking the picture from your hand, a longer exposure (how long? this will discuss in further lessons) will result in a blurry picture because of the uncontrollable shake of hands or movement of subject. In this case, if you can’t control the level of light, the only thing you can do is to increase the sensibility of the sensor (higher ISO level) which will require less light for the picture so a lower exposure time.

In conclusion, the different ISO levels makes the cameras more versatile, allowing us to use them in different light conditions, but with the disadvantage of adding some noise into the final picture.

Now you have an idea about the differences between point and shoot digital cameras and DSLRs and you know which one is best for you. The next step is to actually buy the camera. In the next few lessons I will explain to you a couple of very important technical aspects that are essentials in choosing the right camera from the vast number of models that exists on the market today.

In every camera’s specifications you will find the number of megapixels that it has. But what is a megapixel? A megapixel means 1 million pixels. A pixel is a single point in a graphic image. All graphic images are made up of thousands of tiny points. If your camera is 5 megapixels, it means that any pictures it takes will consist of 5 million of these pixels (on its highest quality setting). Generally, 5 megapixels is enough to print good quality 8x10s. But just because one camera has a certain amount of megapixels doesn’t mean that it will take better pictures with one with a lower amount. There are many factors which affect this, including build quality, type of camera, etc.

If you’re just planning on printing small prints of your photos, or viewing your photos on a computer, you can do this with a lower number of megapixels. But if you want to print quality 8x10s, you will need a bigger number of them. For a quality print, you’d want to start with a photography which contains at least 240 DPI (or dots per inch), 300 DPI would be even better, but 240 is enough. So, for a 4×6 print at 200 DPI, we would need an image size of 960×1440 pixels or better. For a 5×7, we would need 1200×1680, and for an 8×10 we would need 1920×2400 or greater. Now, most 5 megapixel cameras produce an image of around 2592×1944, which when printed at 240dpi comes out to a 10.8″ x 8.1″ print. So, with a 5 megapixel camera you could print 8x10s but only is you are not cropping your image.

Why isn’t more megapixels always better? Camera companies keep increasing the number of megapixels and now even some point and shoot cameras have well over 10 megapixels. But does this mean that they will take pictures of better quality than older models with lower number of megapixels? The answer is no. By continuously increasing the number of megapixels which cameras can output, the camera companies are not paying as much attention to quality as they should. Just because you are cramming more pixels into a photo doesn’t mean that the pixels are sharp enough for there to be any discernible increase in image quality. So, while your pictures may be getting larger, they might not even be sharp enough to be printed at this larger size, merely because there was an increase in pixels, but not an increase in quality. In theory, more megapixels would mean a nicer photo, but in actuality it may just mean a terrible photo composed of more dots.

Once you get past 4 megapixels or so, the resolution stops mattering as much, and optical quality comes more into play. This is why a 8 megapixel DSLR camera will take better pictures than a 10 or 12 megapixel point and shoot digital. Another fact worth mentioning is that DSLRs have larger sensors than a typical point and shoot. These larger sensors produce much less noise than their point and shoot rivals, leading to a much cleaner shot.