HDR- A Simple Explanation

Saturday October 1, 2011

HDR- A Simple Explanation

     When I was teaching, I always tried to explain a concept or lesson in very simple ways. Personally, I find that most books on Photoshop leave out too many steps, and you end up needing to re-read what was written. So here's my small simple lesson on HDR.

        For this post, I decided to show you what HDR can truly do. However, the results are "imperfect". For the original photo session, I would have needed to bracket more, and carefully watch how I placed my lights. You'll understand as you read further.

      HDR is great when you you are trying to photograph a room interior, but the exposures of the bright ares (highlights) and dark areas (shadows) are too far apart. What that means is that your camera simply cannot capture such a big spread of light and dark tones! So what do you do? You take a number of images (on a tripod of course) with the same f-stop, but with different shutter speeds.

     By bracketting  or shooting a whole number of exposures of the same scene but some overexposed and underexposed, you will then have a  spread of exposures recorded for the dark areas and bright areas, and middle areas, or for shadow detail, mid-tomne detail, and highlight detail.

     For my photo, I wanted to show you what you could do if you only had 1 light. A flashlight would even work for this exercise! What I did in this exercise is simply move my lights around, as if I only had 2 lights. However, for a "real studio shot", I would use as many as I needed.  So let's start, and you'll soon easily understand what I'm saying.

Here are 6 images all of the exact same content and camera angle and f-stop.

The shutter speeds were different depending on how the meter read the exposure.

I had 2 lights, but they could not do everything that I wanted in terms of the lighting.

So, I simply repositioned the 2, and in some cases, I only used 1 light.

I've added the same photos below to explain what the lighting is doing in each image.

1. Overall light for the flowers

2. A background light

This  separates the flowers from being "lost" in the background,

 as well as giving the photo a sense of depth.

3. A side light for 3D

4. An "accent light"

This adds a "touch" of light to a part of the flowers

to add highlights, and 3D.

5. Another "separator" light

This  one separates the glass vase from the material 

6. A "detail" light

This light is lighting the folded large leaf inside the vase,

as well as giving the glass some shine and lustre.

I am going to use the HDR Pro command  for the 6 images in Photoshop 

If the files do not merge, you may have to change their exposures.

Remember that HDR works when the images have "bracketed exposures".

So you may have to change the 6 exposures to reflect that. In other words, change the exposures from "normal, to 1/2 stop under, 1 stop under,  1/2 f-stop over, 1 f-stop over, and 1 1/2 f-stops over.

How? just adjust the image as you normally do in Photoshop.

So here is the HDR image.

The green represents bad exposure

I'm going to need to use the "magnetic lasso".

Why?

Because I wasn't watching where I was placing my lights in each image, 

I have a purple-blue shadow that looks "strange"

The magnetic lasso will capture the  purple-blue shadow

I then go to the "Replace Color" command

I then use the "rubber stamp" to gather yellow 

and then put in the purple-blue area to replace those colours with yellow.

Gathering the yellow with the rubber stamp

Using the rubber stamp to replace

 the purple-blue with the yellow

Select >> Deselect to remove the area that was selected by the "magentic lasso"

The HDR Image with the bad exposure and noise in green.

Also, the Vase and flowers are tilted!

The Straightened Image with a "problem".

I need to reframe the image, and eliminate the white in the photo.

The "rectangular Marquee" tool is used to frame the image.

You then:

1. copy the framed (dotted line) content

2. Create a new file

3. Past the content from step 1

4. Flatten or merge layers

5. Save new file

The Final Image

There are still some "faults", but overall I hope you understood the  post.

To Sum-Up

1.  Cameras cannot record the wide range of light and dark areas of a scene

or

If you have a limited number of lights to work with

2. You shoot the same scene or set-up with the same f-stop, but with different shutter speeds

3. The # 2 step, then allows you to capture detail both in the dark and light areas of a scene.

4. HDR (High Dynamic Range) can now be employed in Photoshop

5.  HDR will "blend" the lightest and darkest tones in a scene to  come up with 1 single image

6. There will always be some "problems" but they can be overcome with the regular other Photoshop of Imaging Software menus and commands

7. The next generation of digital cameras will have HDR built-in to the camera!

If:

1. You have any questions

2. Any comments

3. Found errors in what I wrote

4. Still cannot understand what I wrote,

then, please send me an e-mail, and I'll be glad either to answer you personally or simply re-write what I wrote.