The Digital Fingerprint of The Image
In all the years I’ve been exposed to digital photography around my photography workshops I’ve often overheard photographers talking about the perfect histogram. These photographers would say things like a perfect histogram displays a nice bell curve when viewing it in the graphic scale, and still other photographers would say it needs to look like a nice mountain range across the LCD display. I’ve even witnessed photographers telling other photographers, while looking at the histogram on the back of their digital camera, “That’s a bad histogram.”
I naturally interrupt these photographers and stress that there are no bad histograms, only bad exposures. Every histogram is perfect because a histogram is a graphical representation of the photo’s pixel intensity values that you’ve captured—the digital fingerprint of the image! Not to mention, histograms don’t have to look horizontally even from end to end the first time you view them on the LCD monitor of your digital camera.
They are a direct representation of what a photographer has captured (total number of pixels at different intensity values of the RGB scale) including whether the exposure is correct or incorrect, so the graphical scale itself will always vary in appearance. The odds of finding an identical matching histogram are no different than the odds of finding two identical snowflakes. The “key” or legend of a histogram is shadows are on the left, highlights on the right, middle tones in the center.
Basically histograms exist so you can verify that you’ve kept your image detail in the highlights and the shadows, which will naturally ensure your image is exposed correctly in the mid-tones. Histograms don’t lie. Think of histograms as what sheet music is to a musician. Histograms display the “musical notes” of photography, aka the harmony in the tonal range between the shadows, middle tones and highlights.
The key to histograms is learning how to read them in relation to what you’re trying to capture with your digital camera. For example, if you are in studio shooting a high-key set, then chances are your histogram is going to show more information on the right, or highlight side of the graph. If you’re shooting a low-key set, then the shift is to the left of the histogram, or shadow side. Overtime you’ll learn how histograms match your scenes.
For example, if your captured scene is correctly exposed and has an even tonal ranged throughout the middle tones, shadows and back to highlights, you will have that perfect mountain bell curve graphical representation. I can’t stress how important it is for photographers to understand what their histograms are telling them, yes they talk to you and I like to call histograms the modern light/flash meter. The histogram display is a tool you can master by simply paying attention to what they look like for given scenes, skin colors, colors in general, shadows, highlights, etc.
Now let’s pretend your captured scene is a nice outdoor shot of the mountains with trees, shrubs, and taken in the colorful season of Spring. Seven months later you go to that same spot, same camera, same camera settings (think Sunny 16 Rule here) and after you take the picture your histogram is more to the right side—so ask yourself why? Well first of all the spring colors are gone and so is most of the vegetation as it’s covered with snow! Snow is the main highlight in your histogram.
Histograms outside the camera are also used for when working with image editing software and editors have to deal, along with printers, with clipping and other problems caused by improper post-production. However, this article is on general photography histograms and not post-production histograms, so we’ll save that topic perhaps for a future blog article. For now, the main fundamental any photographer should focus on is to understand your histograms and how properly exposed image captures look on a histogram in relation to what you’ve captured.
A great example is the two photos in this article. The first one, is high-key, so naturally if the exposure is correct, most of the graphical data will shift the histogram to the right side, or highlight side. If the data is shifting more to the shadow side, or left, then the photo would be judged as underexposed. The third photo, below, is a low-key image so the data is displayed to the left, or shadow side, when properly exposed. If the histogram has more data toward the highlights, or right side, then the image is judged as overexposed and the photographer would make the proper adjustments to correct the exposure until the data more accurately represented the scene, in this case, more blacks than whites.
Master understanding histograms, and you will master your photography. Remember, it isn’t about bell curves or mountain range looking histograms, it’s about getting it right in the camera and histograms will help you get their if you take the time to understand their indirect message.
With that I close and hopefully we’ll see you at one of our upcoming photography workshops or photography adventures so you can show me your histograms as you take beautiful photos. As always I also ask you not to forget the men and women who serve so patriotically to protect your country, God Bless them, their families and friends.