Take the help of Histogram

Working digitally has a number of benefits, one of the most important being that the colour, brightness and tonal values of the individual pixels that make up the image are recorded as soon as the image is taken.
These values can be reviewed in two ways on the camera's LCD screen - firstly, as the image itself and secondly as a graphic tonal represenattion which is known as a histogram.Being able to interpret histogram will help you to assess whether or not your image has the acceptable tonal value that make for a well exposed shot.

A histogram can normally be called up on the LCD screen on the back of your camera when shooting or playing back images. It is the form of graph where the x-axis (horizontal) represents the entire digital tonal range from black to white (0 - 255), while the y - axis (vertical) represents the number of pixels with a specific tonal value. The right side represents the maximum white values your camera can capture. On either end of the histogram the light values contain no detail. They are either completely black, or completely white. The top of the histogram (top of mountain peak) represents the number of different colors, a value you cannot control, so it is for your information only. We are mostly concerned with the left and right side values of the histogram, since we do have much control over those. (Dark vs. Light). An ideally exposed image would generate a symmetrical,humped shape histogram that smoothes gently out to the black and white points at either end of the histogram.

Below are some of the examples which will help you to understand Histogram.

As it is obvious this picture is underexposed and you can see in the histogram on the right corner of the picture. The pixels are bunched up on the left side of the histogram and there are very few pixels on the right side. This picture can be corrected by increasing exposure. This is discussed in previous blogs.

Same picture was taken with increased exposure and you can see in the histogram that pixels are spread more as compared to previous one and picture contains more detail.

This picture is overexposed. There are very few pixels in the dark areas (left side) and the pixels on the white side (right side) are climbing up the right hand border. This picture can be corrected by decreasing exposure as discussed in previous blogs.

These pictures are correctly exposed as all the pixels falls within the histogram range.

Next I will be dicussing about Composition

Metering Modes

In order to produce an image that is not too bright (overexposed) or too dark (underexposed), all digital cameras need a way to access accurately how much light is present in the scene that is being photographed. Now cameras have built-in light meters that measure the light reflected from the subject or from the scene as a whole. The problem for the photographer is that the brightness can vary significantly from one part of the image to the next. For example, the sky is far brighter than the land during sunrise or sunset. If you were to set the exposure manually, the area you should set the exposure for depends on the result you want; normally you would set the exposure for somewhere between the two extemes. The way a camera arrives at this compromise depends on the type of metering system it uses.

How the camera measures light:

The exact method that different cameras use to measure exposure varies from model to model - but essentially there are three types of metering system commonly found on modern cameras. Three modes present in Sony Cybershot DSC-H2 are

1. Centre - weighted metering:

In this mode, the metering is biased or weighted to the centre of the view-finder (three boxes shown in the picture) and then averaged for the entire scene. This mode is very useful when taking portrait shots.

2. Spot Metering:

Spot metering in most cameras takes a reading from the very centre spot (black dot shown in picture) of the viewfinder (In Sony Cybershot it has flexibility to move this spot) and sets an accurate exposure for that part of the image only. This metering mode should be used when the subject is correctly exposed, no matter how much (or how little) light is falling on the surrounding areas, or during close-up photography.

In the above picture spot metering was used and a part of this picture was overexposed.

Both these pictures were shot at same time and I used spot metering mode for both but position of the spot was different. Spot was on the sky for the picture on left and it was on the bird for the picture on right.

3. Multi / Matrix metering:

This is most sophisticated of all the metering systems, and is the 'default' mode for the most cameras that offer metering option. It works by taking multiple readings from from various points in the scene, while also assessing the position of the main subject, foreground and back-ground, overall brightness, any front - or backlighting, colour and so on. The camera then compares these readings with a database of thousands of 'typical' photographic scenes and selects the exposure that most closely resembles one in its database.

My experience on Metering:

• Pick the "Center-Weighted Metering" mode when you want the camera to meter the light in a broader area than with spot metering but not the entire frame. With center-weighted metering, you can focus on a larger portion of your frame. This is a good option when you’re taking group photos or portraits.

• Select the "Spot Metering" mode when you have one small subject from which you want to record the light value. Spot metering is handy when your subject is in front of a bright background, such as a sunset. By choosing to spot meter the light from the subject only, your camera will adjust the settings, making your subject visible as opposed to creating a silhouette.

• Choose the "Multi Metering" mode (multi-segment metering) for a good all-around photo. In most digital cameras, this is the default meter setting and it measures the light reflected in all parts of the frame and uses the combination to select the light value. For most purposes, matrix metering is sufficient.
  

Next I will discuss about Histogram

ISO, Sensitivity and Noise in Digital Camera.

According to me a good camera is one which can take clear picture in low light without flash. This feature is achieved by ISO settings. Those who are familiar with film photography will know that different films have different ISO ratings. Even though your camera is most likely not film at all, but rather digital, the ISO setting still does has the same function as older film cameras. ISO determines how sensitive the image sensor is to light. A compact camera like Sony Cybershot have ISO settings of 50, 100, 200 and 400, while a digital SLR will often feature incremental settings of 100, 200, 400, 800, 1600 and 3200. Olympus E420 has a range from 100 till 1600. Higher the ISO setting, the more sensitive the sensor is to light which means signal created by light striking the sensor is amplified to greater degree.

Advantage of high ISO setting - avoid camera shake in low lights.

There is a direct correlation between shutter speed and ISO settings. By increasing the ISO settings, the shutter speed increases proportionately, for example, from 1/15 sec at ISO 50, the shutter speed increases to 1/30 sec at ISO 100 and 1/250 sec at ISO 800. At these later speeds, you'll avoid camera shake and can freeze slow movements.

Disadvantage of high ISO settings - causes grainy picture.

Unfortunately, there is a drawback to using high ISO settings as mentioned earlier amplifies electric signals which is applicable for background noise too which is present in camera's circuitry. This distorts the image signal and creates a speckled or noisy image.

Top left picture (Pic 1) is taken with ISO settings set to 100 and shutter speed was adjusted to 1/3 seconds. Top right picture (Pic 2) in right is the magnified version of Pic 1 which shows that the picture is slightly blurry because of hand shake while clicking the camera.

Bottom left picture (Pic 3) is taken with ISO settings set to 1600 and shutter speed was adjusted to 1/50 seconds. Bottom right picture (Pic 4) in right is the magnified version of Pic 3 which shows that the picture is grainy because of background noise. (click on picture to enlarge)

General Rules and tips for ISO Settings:

• Use an ISO of 100 or 200 when taking photographs outside in sunny conditions.
• If the sky is overcast or it is evening time, then use an ISO within the range of 400 to 800.
• Night time or in cases of low light you might need to set your digital camera ISO to 1600.
• Use Tripod if taking photographs at low ISO settings in overcast / low light conditions.

How to reduce noise from the picture.

• Use camera which has got larger sensors because larger photosites found on such sensors collect light more effectively and thus don't need as much amplification to capture a poorly lit scene as a small sensor.
• Now there are lot of photo editors in market (Adobe, Photosuite, Picassa) which helps to remove noise.

Next I will discuss about interesting stuff : Shooting and Composition.

Digital Photography - Pixel and Resolution

My first experience with digital photography was in 2000 when my uncle presented a 0.5 MP Kodak digital camera. It was an amazing present I liked it a lot and started admiring digital photography from then. Things which I liked about digital camera as compared to analog camera was I can see my shots results instantaneously in the LCD screen and there is no recurring cost of developing and printing to view your shots. You just need to take your shots, connect the camera to computer and download pictures to computer and after that you can email it to your families and friends.

Building blocks of digital cameras is PIXELS, which is a short for 'PIcture ELementS'. An individual pixel carries information that governs its color, the strength of that color, and how light the pixel is displayed. In photography terminology these are termed as (HSB)

1. Pixel's Hue,
2. Pixel's Saturation, and
3. Pixel's Brightness.
   

Each image is made up of million of pixels and number of pixel that an image has dictates the image's resolution.

More Pixel means

1. Higher Resolution.
2. Large Print Size.
3. Large Disc Space.

Pic 1 is taken from 2 MP camera has 1600 x 1200 pixels, size on Hard Disk is 177 KB.

Pic 2 is taken from 6 MP camera ( Sony Cybershot) has 2816 x 2112 pixels, size on Hard Disk is 1.5 MB.

Pic 3 is taken from 10 MP camera (Olympus E420) has 3648 x 2736 pixels, size on Hard Disk is 1.9 MB.

As you might have noticed even though these pictures are taken from different camera of different pixel but still their clarity is pretty much same. That is because of Screen resolution / Print resolution which is measured in pixel per inch (ppi). Photo quality prints is 300ppi and computer's monitor has a standard resolution of either 72ppi (Windows) or 96 ppi (Macintosh). Which means if print area is small lesser megapixel camera will give almost the same kind of clarity as of high megapixel camera. Yes if we need to blow up this image then pic taken from 2MP will be most destorted and from 10 MP camera will be least.

So if we need to take pics to email friends and families and to get small prints we can achieve the same using lower MP camera and no need to spend money on higher MP cameras.

Below is the table which helps to determine what is the best print you can get from the range of 2MP - 12 MP cameras.

Next I will be discussing about ISO and Noise in Camera