Using double developments of one RAW file doesn't increase the dynamic range..
You can adjust a raw image by about the equivalent of one exposure stop in either direction. This will recover data from either the black or the white end that was previously "blown out", but, of course, it may cause data at the other end to be pushed into the "blown out" zone..
The process that your are referring two is to create three different output files from the raw converter, one at exposure -1, one at normal exposure and the other at exposure +1. In Photoshop you then merge sections from the two adjusted exposure files into the normal exposure file to avoid sections of blown highlights or blown shadows.Chris R..
You might want to read this:http://www.adobe.com/digitalimag/pdfs/linear_gamma.pdf.
Anyway, the dynamic range of the scene that is displayed depends on curves. Curves can do a thing called "dynamic compression" that allows you to see more dynamic range in an image. Increasing the brightness of the shadows, while darking the highlights is dynamic compression. The draw back is that it will start to look fake if pushed too far, and it will make noise more apparent..
Here is a normal jpeg (each line is one stop brighter than the line to it's left):.
Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.
And this JPEG shows dynamic compression:.
Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window..
Okay, next question then regarding the technique itself. All the tutorials on this I can find use layer masks in photoshop by manually painting in the areas you want to show through/be blocked. Is there a more automatic way to get the layer mask made? For example, isn't there some way to select just the shadows/highlight below/above a certain threshold to create the mask that way rather than painthbrushing it in?..
The point of processing, presumeably, is to get a photograph to resemble what you perceived when you looked at a scene. The eye/optic nerve/brain is a complex image processor that automatically performs a lot of dynamic range compression along with other processing and these steps are local, that is, the processing changes as the scans across portions of the scene. The resulting perceived scene typically has less dynamic range than the original scene. Cameras with their processing try to imitate this processing. As a first step, the entire dynamic range in an image must be captured. This can be large.
If you do it well, the photograph should resemble what you remembered from the original scene. When I began to be able to do this successfully a few years ago, I soon realized that the photograph was typically displayed on a medium with rather less dynamic range than the original scene and it still looked like I remembered. I also have returned to many locations to validate my memories. Since the photograph matched my memory and the photograph was the result of compressing the dynamic range of the original captured data, I concluded that the eye/optic nerve/brain processing also greatly compresses dynamic range. If this was not true, photography would not work very well..
The answer to your question is that a scene can need a lot of dynamic range to capture the image data and that the same scene as perceived by the eye/etc. and a photograph displaying that scene both have a lot of dynamic range compression. In other words, there are really two dynamic ranges relevant to photography, the one needed to capture the scene on a camera and the one needed to display the final processed image. The first can often be significantly larger than the latter. Hope this helps.Leonhttp://homepage.mac.com/leonwittwer/landscapes.htm..
There is another issue I should mention. Many cameras do not use all of the dynamic range of the captured data to make jpg. My camera puts the jpg maximum brightness about a stop below the maximum that can be captured by the camera (and used if you shoot raw). There also can be some capture dynamic range lost on the bottom end also. This loss of dynamic range of the processed image is above and beyond that discussed in the last message.Leonhttp://homepage.mac.com/leonwittwer/landscapes.htm..