Convert between bit depths, Image size and resolution – Adobe Photoshop CS4 User Manual
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USING PHOTOSHOP CS4
Opening and importing images
Last updated 1/10/2010
RGB images are made of three color channels. An 8-bit per pixel RGB image has 256 possible values for each channel
which means it has over 16 million possible color values. RGB images with 8-bits per channel (bpc) are sometimes
called 24-bit images (8 bits x 3 channels = 24 bits of data for each pixel).
In addition to 8-bpc images, Photoshop can also work with images that contain 16-bpc or 32-bpc. Images with 32-bpc
are also known as high dynamic range (HDR) images.
Photoshop support for 16-bit images
Photoshop provides the following support for working with 16-bpc images:
•
Working in Grayscale, RGB Color, CMYK Color, Lab Color, and Multichannel, modes.
•
All tools in the toolbox, except the Art History Brush tool, can be used with 16-bpc images.
•
All color and tonal adjustment commands, except Variations, are available
•
You can work with layers, including adjustment layers, in 16-bpc images.
•
Some filters, including Liquify, can be used with 16-bpc images.
To take advantage of certain Photoshop
CS4 features, such as some filters, you can convert a 16-bpc image to an
8-bpc image. It’s best if you do a Save As and convert a copy of the image file so the original file retains the full
16-bpc image data.
More Help topics
About high dynamic range images
Convert between bit depths
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Do any of the following:
•
To convert between 8 bpc and 16 bpc, Choose Image > Mode
> 16 Bits/Channel or 8 Bits/Channel.
•
To convert from 8 bpc or 16 bits to 32 bpc, choose Image > Mode
> 32 Bits/Channel.
More Help topics
Convert from 32 bits to 8 or 16 bpc
Image size and resolution
About pixel dimensions and printed image resolution
Pixel dimensions measure the total number of pixels along an image’s width and height. Resolution is the fineness of
detail in a bitmap image and is measured in pixels per inch (ppi). The more pixels per inch, the greater the resolution.
Generally, an image with a higher resolution produces a better printed image quality.