Dynamic Range' (HDR)
Clive R. Haynes FRPS
Using the 'Bridge' facility within 'Photoshop CS2' it's possible to automatically combine two or more separate exposures of the same subject in such a way as to preserve the best tonal components from each image. The result is a composite picture with a well-managed tonal range.
This technique is particularly effective when faced with a subject that has a tonal range beyond which a single exposure, even allowing for the extended capture range that Camera RAW, can cope with.
This particular problem has always been possible to deal with by making a series of exposures ('exposure bracketing') ensuring that at least one shot captures the highlight detail and another shot captures the shadow detail. Each image is opened and its tonal range optimised. Next, the images are be imported, in register, into a single, multi-layer document then by using 'Layer Mask' techniques, the best parts of each image layer are revealed.
Remember that when making the initial exposures a tripod will be necessary to keep the shots in register.
'Photoshop CS2' presents another way of dealing with this High Dynamic Range conundrum.
Place the camera on a tripod and make a series of exposures to capture the complete range of tones - ensure both highlight and shadow detail.
Go to 'Bridge' and open the series of pictures. Select (by Ctrl / Clicking) the required images. The images will be processed one by one and appear as a composite. When the composite appears, a small dialogue box will show and allow the 'White Point' to be adjusted. Also, to the left of the composite, 'thumbnails' appear showing the images that make up the composite. Individual 'thumbnail' images may be turned off (by using the adjacent 'tick box') and the effect upon the composite observed. Note also that the composite image will be 32 bit.
Next, go to the Bridge Menu Bar in and choose Tool > Photoshop > Merge to HDR.
Once the composite exposure has been accepted the picture opens in Photoshop. As 32 bit working not only produces a massive file size but also affords very limited access to program features, it's preferable to change the mode to either 16 bit or 8 bit working. Whichever 'mode' is chosen (via Image > Mode > 8 bit or 16 bit), another dialogue box will appear which enables 'Exposure' and 'Gamma' levels to be set. This dialogue box has an expanding section that allows the 'Toning Curve and Histogram' to be adjusted. Note: the 'curve' may only be adjusted if 'Local Adaptation' is selected from the 'Method' drop-down menu.
|When you are content with the tonal range, click 'OK' and the image opens.|
|At this point the image may be treated as a 'normal' 'Photoshop' file and adjusted / manipulated as needed in the usual way.|
|Please note, this method can only be applied by opening separate exposures made in-camera. It will not function if an attempt is made to open the same image, adjusted to different settings via the 'Camera RAW' dialogue box.|
HDR Composite Image with a Full Range of Tones