HDR HDR is a process for increasing the range of tonal values beyond what a single frame (either film or digital) can produce. It can be used to create more realistic views, or wild extravagant ones What we recognise as an HDR image is actually the effect of tone mapping. THE PROBLEM The problem is most commonly apparent when photographing outside, and the sky either appears bleached, or the foreground too dark, depending on exposure.
Average metered exposure
2 stop over exposed foreground exposure 2 stop underexposed background exposure
dark light Eye (plus brain) dark light Camera Our eyes (in combination with our brain) can operate across a very wide dynamic range. Cameras can t. Traditionally (from film technology) there are a number of ways to deal with this...
Graduated filter Work well when horizon is straight. Not so good for tall foreground objects. No chance to adjust later Small aperture (good DOF) sharpens grad cut-off
foreground exposure Graduated filter
Graduated filter foreground exposure 2 stop ND grad
Graduated filter foreground exposure 2 stop ND grad 3 shot HDR
Polarising filter Reduces dynamic range overall. Saturation increased. Range reduction isn t huge. Affects sky colour and nature of reflections may not be what you want. Up to 2 stop loss
Polarising filter Without polariser With polariser
B/W conversion using colour filters Can be applied when converting to B&W greater control Red filter lightens red, darkens blue Blue filter lightens blue, darkens red Yellow, green etc. Don t just de-saturate in photoshop.
Colour image converted to black and white using blue filter
Dodging/burning Dodging/burning in B&W printing Tricky, expensive (for film). Can be done in colour (for digital). Still limited to dynamic range of a single exposure.
Exposure blending Best to limit to 2 exposures (1 for sky, 1 for foreground). Similar effect to graduated filter, but more controllable
Exposure blending Sky exposure Foreground exposure
Exposure blending
HDR High Dynamic Range dark light Bracketed shots HDR dark light
Shooting for HDR Bracket shots one or two stops difference; as many exposures as required, depending on contrast of the scene, and how far you want to take it. Bracket shutter speed NOT aperture DOF will be affected otherwise. Tripod very helpful, but not essential. Watch your longest exposure times though. VR lens very helpful. Not limited to SLRs set compacts to landscape mode to ensure good DOF, and lock exposure to different parts of the scene if you don t have bracketing. Tripod is a burden for compacts. Shoot RAW higher dynamic range to start with and WB can be adjusted later. Focus and exposure lock needed switch to manual if hands-free; i.e. tripod mounted. Beware moving objects particularly leaves/grass etc. in the foreground. SINGLE SHOT HDR RAW files have an extended dynamic range compared to jpegs. Three frames (max 1.5 stop difference) can be generated from one RAW. Or HDR process single RAW file.
IMPORT AND PREPARE RAW files imported into photoshop, then paste on top of each other as layers. If you don t have sufficiently dark or light frames, additional ones can be created by re-importing RAW at darker or lighter exposures. Best not to go too far, say 1.5 stop max. It is better to darken rather than lighten to avoid noise. align layers using auto settings. I do this even if using a tripod. Crop and/or rotate as necessary, then save each layer as a TIFF (greater range and no compression as opposed to JPG). Turn layers off (save single layer). Call each file: **** dark-2.tiff **** light 2.TIFF **** 0.TIFF Etc. USING DYNAMIC PHOTO HDR Drag your exposures into the main window, and assign +/- EV values. If you re importing RAW or jpeg files straight in, the software should be able to read these from the file. Align pictures if you haven t already done this in Photoshop. You can deal (to a degree) with objects that may have moved between exposures by painting a mask on to all moving object in each frame; the software will tidy them up. Your HDR probably won t look much screens (and paper) can only show 8 bit depth.
TONE MAPPING The HDR image you ve made needs to be compressed to display. Tone mapping controls determine how dynamic you image will be. If the sky is too over the top, try producing two versions one for the sky and one for the foreground layer these together later. Save the final image as a TIFF for best quality. THINGS TO WATCH FOR Less is more if you want realistic images if you don t; go for it! Colour saturation increases markedly and can exacerbate camera colour tint issues. Colour fringing problems get magnified. Grain and/or noise can increase. Dust spots become much more visible. Bright haloes can be generated around objects if the process is pushed too far.
HDR with compact camera
Beware moving leaves
HDR PROCESSING Various software packages are available Photoshop (V10 and later) includes basic HDR and some tone mapping. Photomatix $100 Artizen $45 Dynamic photo HDR $55 Free demos are available to try. See: http://captainkimo.com/hdr-software-review-comparison/
EXAMPLES