Monday, 6 February 2017

A Little HDR


I have been banging on for a while now so I thought I should add something here..
I know some HDR pics are a bit overdone and can be a bit harsh on the eyes. This is a easy mistake to make as when you first start playing the the software you tend to push it to its limits just to see what it can do (and forget to reset it afterwards) . I must confess that I have done this myself in the past.
The main reason for using it is to reduce the excessive Highlights and Shadows that can be found in some pictures. To give a colour boost to a “Flat” picture I find that can be done with one frame.

Some people also say that it reduces noise in dark areas of a picture..

An example of this may be a church interior. Normally the camera will attempt to meter for the average light and in a church this may give very dark interiors with correct light from windows or correct light of the interior with 'Blown Out'* windows.

HDR uses a series of 3/5/7 frames which are the Reference frame with other frames darker or lighter. Personally I use three frames :- Normal, + 2stops under exposed & 2 stops over exposed

Many cameras have the “AE Bracketing” function built in so this can be done automatically (and if you are lucky handheld). If this is not the case you should use a tripod and:

Go to Aperture priority mode (You need a fixed focal length.  The shutter speed will vary.)

1 Take a normal picture
2 Set the exposure adjustment to -2 stops and take a pic
3 Set the exposure adjustment to +2 stops and take a pic

If you check the pics on your LCD you should have something like the following :-
Underexposed by -2 stopsOver exposed by two stops.

Perhaps the easiest way of processing the HDR pics is lightroom.. All you have to do is highlight the three pictures and press CTL H (CMD H on a mac I believe) or “Photo”, “Photomerge”, “HDR”

This will go to the HDR preview screen. On the side of the screen are a couple of tick boxes.
Make sure the auto align box is ticked as this will attempt to correct for movements of the camera.

The other option is for ghosting – this is for anything that might move in the picture (between the 3 frames). I would recommend setting to either “None” or “low” -  This should reduce the processing time required. If there is a large amount of pink areas on the preview set the ghosting higher.

Once you have done this press “Merge” and it will take a short time to process the picture depending on your pc. Once complete it will return to the normal Lightroom screen..

The processed frame might not be visible right away as the you are looking at imported files. You will have to go to your normal “Library” view of the folder

Initial Result of HDR process

At first glance the picture does not look greatly different from your reference image but you now have a greater dynamic range of colours and controls available to you..

By reducing the Highlights & White sliders you should be able to fix that “Blown Out” window and the Shadow & Dark sliders should improve the darker areas of the picture.

The vibrance and saturation sliders will allow you to control the colour (along with the other colour controls)

Also remember these controls can be applied locally by the filters and correction brush as well!

After processing

I believe there are two ways of processing HDR files in Photoshop. As I am not a PS expert I will give the most straightforward.

Open P.S.
“Merge to HDR PRO”

You will be prompted to open your pictures and then a 'Processing Dialogue' will open on the screen.

Photomatix is a HDR processing program that can act as a stand-alone or a Lightroom plug-in
You can download a trial version to play with but this will put a watermark on any pictures it creates. These can be removed by purchasing a license.

HDRefex Pro is part of Google's free (NIK collection) designed to act as a plug-in to LR or PS.
With a little playing around it is possible to run this as a stand-alone program (run the exec file from within the program files folder).


*Blown out -An area where the image appears bright white and the camera hasn't stored detail that may have been available to the naked eye.