Ctc Workshop - Hdr Image Creation

CTC RAW Workshop

Kannan K

Introducing

HDR IMAGE CREATION

What is HDR Image High dynamic range imaging (HDRI or just HDR) is a set of techniques that allow a greater dynamic range of luminances between the lightest and darkest areas of an image than standard digital imaging techniques or photograph can yield. This wider dynamic range allows HDR images to represent more accurately the wide range of intensity levels found in real scenes ranging from direct sunlight to faint starlight.

What is Dynamic Range Dynamic range in photography describes the ratio between the maximum and minimum measurable light intensities (white and black, respectively). Scenes with high variation in reflectivity, such as those containing black objects in addition to strong reflections, may actually have a greater dynamic range than scenes with large incident variation. our eyeslight can see over a range of nearly 24 f-stops.

Most digital cameras use a 10 to 14-bit A/D converter, and so their theoretical maximum dynamic range is 10-14 stops. In practice, the dynamic range of a digital camera does not even approach the A/D converter's theoretical maximum; 5-9 stops is generally all one can expect from the camera.

How to Create the HDR Image 1. Take 3-5 Pictures of the same scene by varying the exposure. 2. Merge all those picture and create the single HDR image. 3. Perform the tone mapping so that HDR image can be viewed in the LDR devices such as printer and compute monitors. 4. Publish to friends and show off your skills…!

Dos and Don’t while taking picture 1. Secure the camera to a tripod. 2. Take enough photos to cover the full dynamic range of the scene. You can try taking at least five to seven photos, but you might need to take more exposures depending on the dynamic range of the scene. The minimum number of photos should be three. 3. Vary the shutter speed to create different exposures. Changing the aperture changes the depth of field in each exposure and can produce lower-quality results. Changing the ISO or aperture may also cause noise or vignetting in the image. 4. In general, don’t use your camera’s auto-bracket feature, because the exposure changes are usually too small. 5. The exposure differences between the photos should be one or two EV (exposure value) steps apart (equivalent to about one or two f‑stops apart). 6. Don’t vary the lighting; for instance, don’t use a flash in one exposure but not the next. 7. Make sure that nothing is moving in the scene. Exposure Merge works only with differently exposed images of the

Photomatix plugin Photomatix Pro is a stand-alone program that creates and processes HDR (High Dynamic Range) images and photoshop, light room and aperture plugins are available. Important Tools Strength Controls the strength of local contrast enhancements. A value of 100 gives the maximum increase in both local and global contrast enhancements. The default value is 70. Light Smoothing Controls smoothing of light variations throughout the image. A higher value tends to reduce halos and give a more natural look to the resulting image. A lower value tends to increase sharpness. The default value is "High".

Important Tools Cont…. Luminosity Controls the compression of the tonal range, which has the effect of adjusting the global luminosity level. Moving the slider to the right has the effect of boosting shadow details and brightening the image. Moving it to the left gives a more natural look to the resulting image. The default value is 1.0. Microcontrast Sets the level of accentuation of local details. The default value is 0. Micro-smoothing Smoothes out local detail enhancements. This tends to give a "cleaner" look to the resulting image. It also has the effect of reducing low magnitude noise such as noise in the sky for instance. The default value is 2.

Introducing

HDR IMAGE CREATION END