# Layman's terms....



## TenaciousTins (Dec 6, 2011)

So I have done some quick research on what HDR or HDRI is but this poor little head of mine feels a bit overwhelmed with the in depth explanations. Can you explain in layman's terms what HDR is? What's the difference between that and a regular image? For instance, some people post "HDR" images, but I don't see the difference between them and a non-HDR picture. Thanks!


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## Big Mike (Dec 6, 2011)

Lets start with what exactly 'Dynamic Range' is.  

When you look at a scene, there will probably be a range of how bright things are.  We can assign a brightness value to each thing/area...in EVs (exposure value).  So for example, the sky might be EV12, the landscape might have areas of EV8, EV6 and EV4.   So to calculate the dynamic range of the scene, you take the brightest value and subtract the lowest (12-4) and we come up with a dynamic range of 8EV (or 8 'stops').  

Now we need to realize that our cameras are only capable of recording detail within it's own dynamic range.  For the most part, digital SLR camera are capturing about 4-5 stops (while maintaining good quality).
So when you go to take a photo of a scene that exceeds your camera's dynamic range...you will have to make a compromise.  If you expose for the shadows, the highlights will be blown out (white).  If you expose for the highlights, then the shadows will be black with no detail.  So it has been our task, as photographers, to make this choice and expose for what we deem to be the most important parts of our scene (or do something to alleviate the problem).  

One way to get around this problem, is the HDR technique.  (High Dynamic Range).  With this technique, rather than choosing one exposure, you take several photos at different exposure values...exposing for the shadows and the highlights.  You then use software to take the best parts from each image and combine them into one image, which will have a greater dynamic range than you could ever capture in a single photo.


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## Rephargotohp (Dec 6, 2011)

Problem is , if you can tell the difference, most likely it was a poorly done HDR or wasn't in fact ever an HDR." HDR" has been used loosely.

HDR, is about capturing an image "As the eye would see" in some instance of photography, what the camera captures already is What the eye can see. In other instances, the eye can see far greater differences in bright to dark than the camera can capture. Using HDRI is a way to first "Capture" what the eye can see ( through multiple varying exposures)" and then with software merging and then Tone-Mapping or placing all the brightness levels into something that displays on screen or in print an image that looks likes what "The eye would see" The end file is actually a Standard Dynamic Range image because that is all that is possible with current monitors or Prints.

for more

What is HDR?

The Definition of HDR


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## 480sparky (Dec 6, 2011)

HDR = High Dynamic Range. HDRI = High Dynamic Range Imaging.  Basically they're the same.

Take a given scene, and you will see light and dark areas.  Depending on the camera used, these light and dark areas may or may not be accurately recorded.  Camera sensors can only record a given range of light & dark.  If the light and dark areas of the scene exceed what the camera can record, then the dark areas will simply be rendered pure black and the light areas rendered pure white.

What HDR does is allow one to take a variety of shots, changing the exposures between them.  Some shots are 'overexposed' to record the details in the shadows (dark areas), and others are 'underexposed' to keep the highlights (light areas) from being blown out.

Software is then used to combine the various exposures so that the 'overexposed' dark areas and the 'underexposed' light areas are rendered more accurately in the final print.

Take a trip over the the HDR forum and browse through some of the Shootouts.


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## shootermcgavin (Dec 6, 2011)

Layman's terms, 1 image that needs more than one exposure like inside a tunnel being dark and outside being light.  Basically exposing for tunnel and then for outside and using the proper exposure of both images blended together.  Normally you'll do more than just 2 shots in HDR but that's the basic premise.


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## 480sparky (Dec 6, 2011)

In a nutshell:

Take an underexposed shot for highlights:









Take a 'normal' exposure:








Then overexpose a frame to get the details in the shadows:










Combine them in software:


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## TenaciousTins (Dec 6, 2011)

OK...I completely get it now. That's exactly what I needed. Thank you so much!


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## Bynx (Dec 6, 2011)

Ya those 4 pictures are worth at least a thousand words (of explanation).


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