19th March 2016 · Técnicas · 0 comments ·

HDR photography

HDR photography

     

We all know that the pupil of the human eye constantly expands and contracts when we are looking around. When we look at an area or an object that has a lot of lighting this shrinks, however, it expands if the lighting is poor or dark.

 

 

     To understand well what is HDR photography is necessary to strongly emphasize that this process makes the human eye, it does so because the eye can only look at one point at a time and not to an environment as does the camera . For this reason the pupil is constantly varying in size.


     Making an analogy with the diaphragm of the camera, we can say that by the photometer that the camera is fitted and measures the amount of light entering the diaphragm will expand / open or contract / will close depending on the amount of light who "sees" at the time of shooting.

 

 

 

     The "problem" with which we are when taking a picture is that, since the photometer makes a single measurement of light (either specific or weighted) shall fix a value for the diaphragm to be the same for all decision points as well are very bright or very dark. Therefore this diaphragm will be suitable for some points decision but too open or too closed to others, so for those points where the diaphragm is correct picture will look good, but those for which the diaphragm should be more closed, the image will we overexposed or too light or "burned" and on the other hand, at those points where the diaphragm should be more open because the lighting conditions are poor, you will leave us this underexposed area, dark demasidao or black directly.

 

 


     What we try to do the HDR technique is precisely "correct this problem," causing both light, medium and dark areas look perfectly fine in terms of lighting in a photograph, which makes it somewhat unreal. But this is just my opinion, what makes it attractive to HDR photography.

 

 

 

     Therefore, to take a picture HDR, I do five to nine pictures obviously letting in more light for dark areas and less light to get clear.

     In a camera, we can do this in two ways:

     - Leaving sets the shutter speed (ie the time it is open the curtain) and varying the diaphragm, more open to more light.

     - Leaving the fixed diaphragm and varying the shutter speed. A longer with open curtain will come more light and vice versa.

     Either of the two options would be worth, but in HDR, we use the second, ie, varying the shutter speed for some reason I mention below:

 

 

Diaphragm more open = less depth of field
Diaphragm more closed = more depth of field

 

     Since the work we will do with several equal, equal but different illuminations photos, apart from using a tripod for pictures leave us exact as the frame is concerned, we need everything in one take us out crisp, also focused us out crisp and focused on all others. And this we can only achieved by maintaining the same aperture diaphragm at all because if we change, we vary the depth of field or frame in which the captured image is sharp.

     Therefore we have no choice but to vary the shutter speed. Actually, as we have the camera on a tripod, shutter speed will not matter too much, but we use the diaphragm.

     Keep in mind that if you are going to photograph a landscape we have to put a very closed so that the depth very large diaphragm and thereby obtain clear to the horizon. Additionally, if we put a closed diaphragm, we may have to put very high exposure times (1 sec., 1/2 sec. Etc) for the purpose of camera movement does not affect us as I said but possibly if you affect us about the picture will get more "noise" the longer you put it.

 

 

                                                                    Sample photo with Long exposure noise

 

 

To take pictures HDR story with the following material to the pictures then at home will process:

 

                                                             Tripod, manual trigger and of course a camera.

 

 

And to make the story with Photomatix HDR process and Photoshop. (Versions to individual taste.)

 

                                                                                         Photomatix

 

 

                                                                                          Photoshop

 

 

For this tutorial I chose this photo:

 

 

 

                                                             --------------------o--------------------

 

 

Shooting:

I made six shots with the camera on the tripod and manual shutter cable.
Data of six shots, except the speed, (they are placed under each photo), were:

Camera: Canon EOS 40D
Objective: Sigma 10-20mm
Focal Length: 14 mm
Aperture: f / 16
Priority: Opening
ISO 100

 

1/200 sec

 

 

 

1/100 sec

 

 

 

1/50 sec

 

 

1/25 sec.

 

 

 

1/13 sec

 

 

 

1/6 sec

 

 

     The day was quite cloudy as you can see. The first photo is too dark because, although a speed of 1/200 is a very normal speed, I used a fixed aperture of f / 16 for much depth of field as possibly so that the photo had gone well luminosity it would have been necessary to put an f / 5.6

     When we do a series of photographs how are you known by the name of "bracketing" or "bracketing".

     Most of SLR digital SLR cameras have a system by which we can put the minimum and maximum exposure and, depending on the make and model, we make consecutive shots and the camera alone we will doing different shots you see here up. In this case it is called "Auto bracketing" or "Bracketing".

     For convenience, the camera can be put in burst mode, although the Puritans say you should not do so because every time a shot is fired must wait a few seconds for the camera stops moving because the movement produced by the mirror when the curtain rises and may impact on the next shot due to a microbalanceo produced. (This I leave to individual taste)

     For this work I put a three-shot bracketing (which is the maximum allowed my camera) separated by a difference of 1 point exposure between shots, and the camera in burst mode.

     Having made the first three and carefully turned the wheel speeds to bear the photometer 1 point above the last picture taken and made the remaining three.

     This same process we could have done with two, three, four, twenty ... .. they want, from a totally black photography to a completely white but then do not we use, in fact, I personally do not usually use all what I do.

     Once we have the pictures, and we can only make the process of obtaining HDR photo following steps:

     1. We open our Photomatix and select the photos that we will try, File> Open, we mark the files, and click Open:

 

 

     First I open all the pictures of the series and do all the procedure that follows. However, I often repeat but selecting only some photos instead of all. For example with the 1st, 3rd and 5th or the 2nd, 4th and 6th or what I please and make processing them. You have to know that in this post-processing plays a lot with trial and error to get what we want, so it is necessary to take it with patience and time left to do more the better tests.

 

     2. Then do: HDR> Generate> We mark Use opened images> OK
     On occasion, it is possible that pressing OK similar to this screen qppears:

  

 

     The explanation is that assuming that 0 is the correct exposure, Photomatix expected to exhibit interval is the same for all photos, both underexposed (negative values) to the overexposed (positive values).

     In the event that does not happen we will leave this window showing us what Photomatix believes, where he let us change the values ​​if we consider that Photomatix has not played well or leaving it as if it really shows us is right.

     In any case we will press OK.

 

3. It appears this window:

 

 

     I usually leave it alone and press OK. Align source images labeled leaving Photomatix we correct any small misalignment that exists between all selected photos. If we made shots in which there are objects or people moving logically between takes these have moved, in which case tildaremos also reduces ghosting artifacts Attempt to.

 

     4. After clicking OK in the previous window, we see a new window with our photo HDR:

 

 

     5. If you move the cursor over our picture, we can see in the small window Viewer HDR photography as will in all areas after doing next step in Tone Mapping. If we think it is too light or too dark can raise or lower the exposicióncon HDR> Adjust View> Exposure Up to increase exposure F12 or F11 Exposure Down to decrease it. Generally you do not have to do anything and we will continue with the next step.

 

     6. Now we will access the last step is the Tone Mapping. We click HDR> Tone Mapping and leave us the following window:

 

 

     ... And here dear friends, I leave you to your fate. All you see will slip to give you more or less force to the photo, color saturation, softness of light, brightness, etc, etc.

     For reference, there are certain adjustments that I almost always I put more or less the same as are:

                        Gamma: 2.0
                        Black Clip: 0.00%
                        White Clip: 5.000%
                        Light Smoothing: 0 or 1
                        Strength: (above 50, even reaching 100)

 

     7. After several hours :-)) touching the sliding press OK and will appear as the final work on the main window Photomatix:

 

 

     Once here we can save nuetra picture. I usually save in TIFF format for a simple reason. We all know that the JPG format is a compressed format and how the next thing we will do is open the file in Photoshop to make a few tweaks and re-save and possibly return to open to retouch and save again ... and more the quality of our picture is deteriorating more and more when saved since it has to compress each time you save the file running the danger it leaves us the typical bands JPG.

     Therefore File> Save as ...> (choose TIFF) and click Save

 

     8. And, as a final step, open the photo with Photoshop to put the finishing "touches" such as:

 

 

          Image> Adjustments> Levels

          Image> Adjustments> Curves ...

          Image> Adjustments> Hue / Saturation ...

          Filter> Sharpen> Unsharp Mask ...

       etc etc

 

I hope it's helpful for you.

 

 

Enrique Izquierdo

Leave a Comment
Your email address will not be published.
4 + 2 =
View previous | next

Lastest posts