Dynamic Range
Dynamic Range (DR) is most probably the single most discussed aspect of digital photography in forums, magazines and blogs. I believe it has become one of the most powerful marketing tools manufacturers use to influence the buying decision. How often do we read or hear, the smaller sized sensor has less DR, or this camera had poor DR results in the latest DPR review, or full frame is better than APC sized sensors in terms dynamic range. I decided to add this short article on dynamic range and hope to remove some of the "street science" from dynamic range. My previous articles on dynamic range looked more at the technical aspects of what dynamic range is and how it effects the image. For this article I decided to take a very practical approach to explain what it is we see, in terms of the possible effects on image quality and how to best work around the limitations of the average digital image sensor.
Also see the Blog article I wrote on DR
Dynamic Range (DR) definition:-
Dynamic range is the ability of the digital camera sensor to record details equally good in the shadows, the midrange and the bright areas of the image. To see for yourself how difficult it is for the digital camera to record details in dark areas plus bright areas in the same image you can do the following easy test. Let your partner or a friend stand with his or hers back facing to an outside facing window in a room. Take a digital camera and point it to the window, preferably with bright daylight on the outside and take a picture. Study the picture and you will see one or more of the following interesting aspects in the image:-
Possibly the window area is very bright, the rest of the room in the image darker and the person facing the camera is also not well exposed. You can ask yourself the question, is that what you saw with your eyes?
Possibly the darker areas below any furniture in the room has no detail and is only black.
No matter how you try, you could not manage to get a good level of exposure on the person, the details on the outside of the window plus the rest of the room.
Moving closer or further away from the window just worsened the described effects.
Another good example is when you try to take a picture outside in the city streets with a bright blue skyline. If you expose for the area between the buildings and down on street level then the skyline seem to over expose. Vise versa if you expose for the sky line then the street level detail will be poor because it will be under exposed. With these two examples I think you will better understand what it is when we refer to dynamic range.
What do I need to know about DR?
The problem is that the 8 bit JPEG file format does not have enough information “holders” to record all the information available on a bright sunny day. One way of expressing this problem is to say that a bright sunny day could have as much as 16 stops of information and we try to compact that into a 8 bit format JPEG file. I do not want to go into too much detail in this article. Important to know is that by studying the histogram graph one can see if a image was under or over expose plus one one can see if the conditions exceeded the range of the sensor. For example if the conditions was too bright then the camera turns the bright areas to white. In a similar way under exposed areas will just turn black. You will agree that completely white or black areas does not have any unique shade or brightness information.
When you learn more about the different shapes the histogram graph can have, you will see that it is possible to see exactly when the image conditions exceeds the capacity of the 8 bit file format. For example its possible to look at a histogram and to know if a image is clear or if the image has a hazy look. When reading this article one could say that dynamic range are only related to the 8 bit file format. That is not 100% correct because the actual digital image sensor also has a limited dynamic range. Again the typical camera sensor only range between 8,5 and 11,7 stops.
As you learn more about exposure and dynamic range, you will see its not correct to only consider the image sensor or the file format. There are several ways to deal with high dynamic range situations plus most important high dynamic range scenes can help us to create unique looking images. There are wonderful examples of how photographers used dynamic range to create wonderful images or works of art. Please do not allow people to make you doubt you equipment. Digital cameras in general are good today and capable of doing much more than we expect.
There are several ways to master dynamic range. One can basically divide these methods into exposure technique or one could do it using software. If you like to know more about exposure techniques then please ask in the forum area. I the next paragraphs I will discuss a few software techniques one can use to increase the dynamic range. Interesting is that the results will again be saved in JPEG format. The difference is that this time we as the artists tuned the final image.
Adjust DR in Photoshop
The image below is a visual examples of what happens when the dynamic range exceeds the file format or that of the sensor. I edited the same JPEG image to have an under exposed shade area on the left and over exposed skyline on the right.
Having said that it just was not possible to correctly expose this scene. No matter what I tried, in one instance it would over expose like on the right and in the next instance it will under expose as in the image on the left.
One way to fix this limitation is to work with RAW images. RAW files typically offer a 16 bit file format.
Another method is to work with layers in a image editing package like Photoshop Elements. One can use blending modes and layers masks to step by step develop separate parts of the images and to then join the corrected parts into one final image. I used this method on the above two pictures. On the left picture I used the mountain plus skyline and on the picture on the right I used the bottom "green" part. The picture below shows the result using this method.
Another method is the so called High Dynamic Range (HDR) method. This option requires a series of differently exposed images plus dedicated HDR software. This is a fun option and very creative depending on the style of the photographer. HDR images can be very natural looking or they can be creative, the choice is that of the photographer.
The images I used for this article was taken with the Olympus E420. With digital SLR cameras its possible to save images in both JPEG and RAW. At the time of taking this image I did not use the JPEG plus RAW option. I therefor only had the JPEG version of this image when writing the article. This is frustrating because one can do so much more with the RAW version. My advice therefor is to use RAW plus JPEG whenever you can. As your image editing skills improve you will find its great fun to work with RAW images.
Conclusion
In the old film days only aperture and shutter speed were considered to adjust exposure. Film speed also influenced exposures but different to the ISO value in digital photography, the film speed stayed the same for the duration of the type of film used. Instead of having only the 2 variables used in the film days we now have a active third variable, namely ISO. In addition we are faced with limitations as discussed in this article.
In the film days we had only limited access to image editing. Image editing was a hands on process and it was also expensive to set up a home lab. Digital photography has changed that and today there are a number of free editing packages that are very powerful. In the old days the photographer had to master exposure plus it was critical to do things right the first time. Digital photography has opened the the image taking experience and combined with software the limitations are few.
What is the right way and what should be allowed? In the old days photographers had to master their skills based on the given variables. I think its important to to limit digital photography and to allow the modern photographer to work within the new complete set of new variables we see with digital photography.
I hope you enjoyed this article, it surely is a interesting subject. You welcome to ask questions in the forum area.
Siegfried