Converting Between Color Modes; Convert An Image To Another Color Mode; Convert An Image To Bitmap Mode - Adobe Photoshop CS6 User Manual

Converting between color modes

Convert an image to another color mode

Convert an image to Bitmap mode

Convert a color photo to Grayscale mode
Convert a Bitmap mode image to Grayscale mode
Convert a grayscale or RGB image to indexed color
Convert an image to another color mode
You can change an image from its original mode (source mode) to a different mode (target mode). When you choose a different color mode for an
image, you permanently change the color values in the image. For example, when you convert an RGB image to CMYK mode, RGB color values
outside the CMYK gamut (defined by the CMYK working space setting in the Color Settings dialog box) are adjusted to fall within gamut. As a
result, some image data may be lost and can't be recovered if you convert the image from CMYK back to RGB.
Before converting images, it's best to do the following:
Do as much editing as possible in the original image mode (usually RGB for images from most scanners or digital cameras, or CMYK for
images from traditional drum scanners or imported from a Scitex system).
Save a backup copy before converting. Be sure to save a copy of your image that includes all layers so that you can edit the original version
of the image after the conversion.
Flatten the file before converting it. The interaction of colors between layer blending modes changes when the mode changes.
Note: In most cases, you'll want to flatten a file before converting it. However, it isn't required and, in some cases, it isn't desirable (for
example, when the file has vector text layers).
Choose Image > Mode and the mode you want from the submenu. Modes not available for the active image appear dimmed in the menu.
Images are flattened when converted to Multichannel, Bitmap, or Indexed Color mode, because these modes do not support layers.
Convert an image to Bitmap mode
Converting an image to Bitmap mode reduces the image to two colors, greatly simplifying the color information in the image and reducing its file
size.
When converting a color image to Bitmap mode, first convert it to Grayscale mode. This removes the hue and saturation information from the
pixels and leaves just the brightness values. However, because only a few editing options are available for Bitmap mode images, it's usually best
to edit the image in Grayscale mode and then convert it to Bitmap mode.
Note: Images in Bitmap mode are 1 bit per channel. You must convert a 16- or 32-bits-per-channel image to 8-bit Grayscale mode before
converting it to Bitmap mode.
1. Do one of the following:
If the image is in color, choose Image > Mode > Grayscale. Then choose Image > Mode > Bitmap.
If the image is grayscale, choose Image > Mode > Bitmap.
2. For Output, enter a value for the output resolution of the Bitmap mode image, and choose a unit of measurement. By default, the current
image resolution appears as both the input and the output resolutions.
3. Choose one of the following bitmap conversion methods from the Use pop-up menu:
50% Threshold Converts pixels with gray values above the middle gray level (128) to white and pixels with gray values below that level to
black. The result is a very high-contrast, black-and-white representation of the image.
Pattern Dither Converts an image by organizing the gray levels into geometric configurations of black and white dots.
Diffusion Dither Converts an image by using an error-diffusion process, starting at the pixel in the upper-left corner of the image. If the
pixel's value is above middle gray (128), the pixel is changed to white—if below it, to black. Because the original pixel is rarely pure white or
pure black, error is inevitably introduced. This error is transferred to surrounding pixels and diffused throughout the image, resulting in a
grainy, film-like texture.
Halftone Screen Simulates the appearance of halftone dots in the converted image. Enter values in the Halftone Screen dialog box:
For Frequency, enter a value for the screen frequency, and choose a unit of measurement. Values can range from 1.000 to 999.999 for
lines per inch and from 0.400 to 400.00 for lines per centimeter. You can enter decimal values. The screen frequency specifies the ruling
of the halftone screen in lines per inch (lpi). The frequency depends on the paper stock and type of press used for printing. Newspapers
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