Understanding Dynamic Range Of Colors

In real world, there is nothing called real white or real dark. It is only representation of degree of light source intensity and subject's reflectivity. If somebody says something is white, that means light intensity on that subject is maximum and that of black is minimum. But there is no real measurement which is absolute white and which is absolute dark and same thing applies to photography. I think that is the reason there is a term called "dynamic range of colors" and we are going to discuss about it today. When we talk about dynamic range, we are talking about range of brightness. For example dynamic range of our eyes refers to the range of brightness in which we can see. When you go to the room that is so dark you can't see anything, then you are outside of the dynamic range of your eyes. Similarly if you are driving to the direction of the sun, you might have trouble seeing road properly and you are sort of blinded by powerful lights of sun. And that means you are again outside of dynamic range of your eyes; you are experiencing more light than your eyes can handle. Obviously more dynamic range you can perceive, more places you can see. Dynamic range also impacts your perception of color because colors have brightness. So when you can see better range of brightness, you can probably see greater range of colors.

In terms of photography, dynamic range gives the ratio between white and dark subject and describes the ration between maximum and minimum intensity of light (contrast ratio). As you all know that light is measured at each pixel level (a digital camera uses a sensor array of millions or tiny pixels to produce the image) and each of those pixel contains "photosite" which collects and stores photons when exposure begins by pressing shutter release button.  When the exposure is finished, the quantity of photons in each photosite gives various intensity levels of light which is determined by bit depth (0-dark and 255-white for an 8-bit image). If each photosite contains 1024 photons, then the contrast ratio would be 1024:1. Generally speaking, dynamic range of colors is higher for DSLR cameras than the compact point and shoot cameras even if their pixel is same because of the bigger sensor size in DSLR cameras (bigger sensor size means bigger photosites and hence more lights can be captured). Usually in digital cameras, the most common method of representing a dynamic range is f-stop which is power of 2. A contrast ratio or 1024:1 would there be represented as having dynamic range of 10 f-stops.

You should already be familiar with photographic concept, stop of light or f-stop. Every time the light in the scene doubles, we say that light has been increased by one stop. Similarly if the light scene is halved, we say it is decreased by one stop. In photography, f-stops are measure of the lights. If you measure the dynamic range of your eyes that is the range from darkest light to brightest light that you can perceive, you find that your eyes have around 18-24 stops worth of dynamic range. And today's most advanced DSLR camera might have 10-14 stops of dynamic range.

Basically, anytime when there is a big difference between the brightest object and the darkest object in your scene, you have probably gone beyond dynamic range of your camera. If we consider each photosite as a bucket, we can assume photons as a water drops. If the bucket is full, photons will overflow and a photosite having overflown photons means it is saturated for lights and hence defining the camera's white level and no more colors can be represented within that photosite. Below is the picture where I tried to illustrate the point where photosite is overflown by too many photons and hence loosing details of the image.

Dynamic range of colors - bright scene

Similarly, if photosite couldn't capture enough photons, it will loose the contrast in the picture and hence producing only dark side of the image.

Dynamic range of colors - dark scene

With the digital cameras, it's almost impossible to get all the colors in single image specially when there is too much variation of light. That is why the concept of HDR photography is becoming popular in which we combine multiple pictures using different HDR algorithms to create a single HDR image which should give us maximum dynamic range of colors.

Dynamic range of colors - HDR image

In creating a image by using HDR technique, we take multiple shots from the very dark image to the very white image using the Bracketing technique where we get multiple levels of contrast and by combing them into a single picture, we get the maximum possible range of colors.

Is Post Processing Necessary In Digital Photography?

This post is a part of our Q&A section. If you want to submit your question, please use the form in the Contact page.

Afrina (Kuala Lumpur, Malaysia) asked : I am not a pro photographer but I enjoy photography. When I visit the flickr and other photographers' website or blog, they have a collection of amazing photographs. Some of the photographers also revel what editing tool they used and what was done on the picture during post-processing. Do you think it is necessary to use any software to make your photograph look good?

I have seen this confusion on many photographers from different level of expertise. I think this wouldn’t be that much of interesting topic when you are just starting photography but as you progress more on your composition skill and master your camera settings, the next stop would be the editing skill. I also went through the same situation a while ago and started looking my option for post-processing. When it comes to the editing, different photographers have different views about the process and the tools they would like to use. Even after reading many blogs and online tips, the answer was not so clear to me whether the editing skill is a must to have to enhance your photography or it is just an optional choice. Some of my friends jokingly say that, if you are using Photoshop to enhance your photographs then it's not a photography, it is a Photoshopgraphy. I find it funny but meaningful statement at the same time. When I see other photographers’ work, I forget all the critics and feel like editing is a must have skill set and is one of the important part of digital photography. After doing much research, I wrote a blog about post processing where I discussed more about the post-processing and listed down some of the best known post-processing software in the market.

To be honest, it is not always necessary to use a software and process the pictures but sometimes you find it necessary just to tweak some settings, adjust colors and lights or even crop the sides. Some people think cropping is not really a post processing but I would say, if you use any software to manipulate the photographs by any means, it is a post-processing because you processed the photographs after taking it out from the camera.

Let me present you an example of a photograph, before and after processing it, and you shall decide if post-processing is really necessary or not. And also, as always, I welcome your comments as well.

Before post processing

I took this photograph of the Lincoln Memorial Reflecting Pool last year. When I came home and downloaded the picture from the camera, I felt good about it's composition (symmetry) but felt like I was missing something on the picture. I was not really happy with the color contrast and thought of playing with the color tones and the contrast and see how will it become. I started editing the picture using Capture NX2, one of my favorite software to process RAW images. During the processing of the image, I increased the color contrast and adjusted the brightness of the picture which transformed the picture into the next level. Just a couple of small tweaks boosted the mood of the image and the result was very impressive. The picture looked more vibrant and lively after the post-processing.

After post processing

The result is in front of you and I let you decide whether the post processing is really necessary in digital photography or not. But looking at the transformation this image got, I think you would agree that post-processing is an essential tool and may greatly help you to enhance the picture if done correctly. You just have to be careful about not doing it too much, otherwise it may not look natural.

RAW Vs JPEG Picture Format

RAW files are the exact representation of your subject captured by the camera sensor without any modification. RAW format retains more detail information about the picture and camera setting which you can adjust later during post-processing. Every camera manufacturer has their own proprietary format to store RAW files. Nikon uses NEF format to store RAW files and Canon uses CRW into older camera models and CR2 into newer models. Usually, RAW format stores information into 12 to 16 bit data. Camera always captures the data into RAW format first and if you are using JPEG mode, camera processes it using built-in algorithm to handle the white balance, contrast, saturation, sharpness and other settings that is set into your camera and compresses it into JPEG format to produce a 8 bit of data (JPEG) file. That means you will loose some details during the compression, which is pretty obvious given the reduction of information. I once read Ken Rockwell's comment about shooting in RAW mode where he says and I quote, "I never shoot RAW. Why would I? Raw is a waste of time and space, and doesn't look any better than JPG even when you can open the files". Later he added, "Cameras all start with raw data and convert this data to JPG images with hardware in the camera. They then throw away the raw data since it's no longer needed. Some fancier cameras save this raw data so you can use software to do the same thing the camera's hardware did, later".

In my view, shooting in either RAW format or JPEG format is your personal choice but the only difference is, if you shoot RAW, you have the flexibility to adjust settings later on the computer but in case of JPEG format, camera already did that job for you and you have to trust it’s algorithm for your final image since there is very less room left for further adjustment due to the loss of data. It is up to you whether you want to spend your money on getting software and use your time for further processing of your image on the computer or let your camera do that job for you. RAW mode is designed for someone who wants to do experiment with the photograph by applying different settings during editing. And if you are a professional wedding photographer for example, shooting in a RAW mode might be a no-brainer. You can't re-shoot the wedding once its done. And if you need to adjust something later on the picture without loosing details, you can do so with a greater flexibility if you shoot in a RAW mode. One thing you might want to consider while shooting in a RAW format is a memory. As we discussed earlier, RAW file uses 16 bit data format compare to the 8 bit format for JPEG file. RAW format takes almost double the size of JPEG format. If you are shooting all day event (using RAW format) capturing hundreds of photos, you might have to consider the memory size of your camera as well. It is always a good idea to carry an extra memory in your camera bag but if you are shooting in a RAW mode, that might become a necessity.

In my opinion, if you are smart enough to use a post-processing software for editing pictures, it is a good idea to shoot in a RAW format. But if you are not confident enough on using computer software to edit the pictures, it's better to believe in your camera and let it process for you. If you really want to see the differences between two formats, you can also use RAW+JPEG mode (most of the modern DSLR camera supports dual mode) which saves both files; one in JPEG format and another in RAW format. And later, you can try processing both formats using software and see the difference yourself. Reminder - since it keeps both file formats of the same image into your camera memory, you will have to be more careful about the memory space.

Personally, I shoot JPEG Fine for the most of the friends and family events. But I also shoot RAW when I do night cityscapes, fireworks or landscape photography and use Nikon Capture NX2 for post-processing. Please feel free to share your experience and tell us about views on shooting RAW Vs. JPEG.

Update : I switched from Capture NX2 to Adobe Lightroom in 2017