About high dynamic range images

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Photoshop support for 32‑bpc images

The dynamic range (ratio between dark and bright regions) in the visible world far exceeds the range of human vision and of images that are displayed on a monitor or printed. But whereas human eyes can adapt to very different brightness levels, most cameras and computer monitors can capture and reproduce only a fixed dynamic range. Photographers, motion picture artists, and others working with digital images must be selective about what’s important in a scene because they are working with a limited dynamic range.

High dynamic range (HDR) images open up a world of possibilities because they can represent the entire dynamic range of the visible world. Because all the luminance values in a real-world scene are represented proportionately and stored in an HDR image, adjusting the exposure of an HDR image is like adjusting the exposure when photographing a scene in the real world. This capability lets you create blurs and other real-world lighting effects that look realistic. Currently, HDR images are used mostly in motion pictures, special effects, 3D work, and some high-end photography.

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Merging images of different exposures to create an HDR image

In Photoshop, the luminance values of an HDR image are stored using a floating-point numeric representation that’s 32 bits long (32‑bits-per-channel). The luminance values in an HDR image are directly related to the amount of light in a scene. This is not so with (non-floating point) 16‑bits-per-channel (bpc) and 8‑bpc image files, which can store luminance values only from black to paper white; this represents an extremely small segment of the dynamic range in the real world.

Photoshop offers layers support for 32‑bpc images, and many tools, filters, and commands can be used with 32-bpc images. (For more information, see below.) In addition, you can specify new images as 32 bpc in the New dialog box.

You can also paint on 32‑bpc images in Photoshop. The Adobe Color Picker lets you specify colors that have a brightness intensity that exceeds 1.0 (the equivalent of the 255 level in an 8‑bit RGB document). See also About the HDR Color Picker (Photoshop Extended).

You can create an HDR image using multiple photographs, each captured at a different exposure. In Photoshop, the Merge To HDR command lets you create HDR images from multiple photographs. Because an HDR image contains brightness levels that far exceed the display capabilities of a standard 24‑bit monitor or the range of tones in a printed image, Photoshop lets you adjust the preview of the HDR image so it can be viewed on a computer monitor. If you need to print the image or use Photoshop tools and filters that don’t work with HDR images, you can convert the HDR image to an 8‑ or 16‑bpc image.

For a video on editing and merging images from Lightroom, see www.adobe.com/go/lrvid4121_ps.

Photoshop support for 32‑bpc images

Use the following tools, adjustments, and filters with 32‑bpc HDR images:

Adjustments: Levels, Exposure, Vibrance, Hue/Saturation, Channel Mixer, Photo Filter.
Note: Although the Exposure command can be used with 8‑ and 16‑bpc images, it is designed for making exposure adjustments to 32‑bpc HDR images.
Blend Modes: Normal, Dissolve, Darken, Multiply, Lighten, Color Darken, Linear Dodge (Add), Color Lighter, Difference, Hue, Saturation, Color, and Luminosity.
Create new 32‑bpc documents: In the New dialog box, 32 bit is an option in the bit depth pop‑up menu to the right of the Color Mode pop‑up menu.
Edit menu commands: All commands including Fill, Stroke, Free Transform, and Transform.
File Formats: Photoshop (PSD, PSB), Radiance (HDR), Portable Bit Map (PBM), OpenEXR, and TIFF.
Note: Although Photoshop cannot save an HDR image in the LogLuv TIFF file format, it can open and read a LogLuv TIFF file.
Filters: Average, Box Blur, Gaussian Blur, Motion Blur, Radial Blur, Shape Blur, Surface Blur, Add Noise, Differences Clouds, Lens Flare, Smart Sharpen, Unsharp Mask, Emboss, De-Interlace, NTSC Colors, High Pass, Maximum, Minimum, and Offset.
Image commands: Duplicate, Image Size, Canvas Size, Image Rotation, Calculation, Variable, and Trim.
View: Pixel Aspect Ratio (Custome Pixel Aspect Ratio, Delete Pixel Aspect Ratio, Reset Pixel Aspect Ratio, etc.)
Layers: New layers, duplicate layers, adjustment layers (Levels, Vibrance, Hue/Saturation, Channel Mixer, Photo Filter, and Exposure), fill layers, layer masks, layer styles, supported blending modes, and Smart Objects.
Modes: RGB Color, Grayscale, conversion to 8 Bits/Channel or 16 Bits/Channel.
Pixel Aspect Ratio: Support for square and non-square documents.
Selections: Invert, Modify Border, Transform Selection, Save Selection and Load Selection.
Tools: All tools in the toolbox except: Magnetic Lasso, Magic Wand, Spot Healing Brush, Healing Brush, Red Eye, Color Replacement, Art History Brush, Magic Eraser, Background Eraser, Paint Bucket, Dodge, Burn, and Sponge. Some tools work with supported blend modes only.

To work with certain Photoshop features, you can convert a 32‑bpc image to a 16‑bpc or an 8‑bpc image. Do a Save As and convert a copy of the image file to preserve the original.