About image modes

An image mode determines the number of colors that can be displayed in an image and can also affect the file size of the image. Photoshop Elements provides four image modes: RGB, bitmap, grayscale, and indexed color.

Image modes
Image modes

A. Bitmap mode B. Grayscale mode C. Indexed-color mode D. RGB mode 

Bitmap mode

Uses one of two color values (black or white) to represent the pixels in an image. Images in bitmap mode are called 1‑bit images because they have a bit depth of 1.

Grayscale mode

Uses up to 256 shades of gray. Grayscale images are 8‑bit images. Every pixel in a grayscale image has a brightness value ranging from 0 (black) to 255 (white). Grayscale values can also be measured as percentages of black ink coverage (0% is equal to white, 100% to black).

Indexed Color mode

Uses up to 256 colors. Indexed-color images are 8‑bit images. When converting into indexed color, Photoshop Elements builds a color lookup table (CLUT), which stores and indexes the colors in the image. If a color in the original image does not appear in the table, the program chooses the closest one or simulates the color using available colors. By limiting the panel of colors, indexed color can reduce file size while maintaining visual quality—for example, for a web page. Limited editing is available in this mode. For extensive editing, you should convert temporarily into RGB mode.

When you choose a different color mode for an image in the Edit workspace (Image > Mode > [image mode]), you permanently change the color values in the image. You might want to convert into a different mode for several reasons. For example, you may have an old scanned photo in grayscale mode in which you want to add color, so you would need to convert it into RGB mode. Before converting images, it’s best to do the following:

  • Edit as much as possible in RGB mode.

  • Save a backup copy before converting. Be sure to save a copy of your image that includes all layers in order to edit the original version of the image after the conversion.

  • Flatten the file before converting it. The interaction of colors between layer blending modes will change when the mode changes.

Opomba:

Hidden layers are discarded and images are flattened automatically when you convert them into bitmap or indexed-color mode, because these modes do not support layers.

RGB Color mode

The default mode of new Photoshop Elements images and images from your digital camera. In RGB mode, the red, green, and blue components are each assigned an intensity value for every pixel—ranging from 0 (black) to 255 (white). For example, a bright red color might have an R value of 246, a G value of 20, and a B value of 50. When the values of all three components are equal, the result is a shade of neutral gray. When the value of all components is 255, the result is pure white; when the value is 0, the result is pure black.

Convert an image to bitmap mode

To convert an image to bitmap mode, you must first convert it to grayscale mode, simplifying the color information in the image and reducing its file size. Converting to grayscale removes the hue and saturation information from the pixels and leaves just the brightness values. However, because few editing options are available for bitmap-mode images, it’s usually best to edit the image in grayscale mode and then convert it.

  1. Choose Image > Mode > Bitmap.
  2. If the image is RGB, click OK to convert it to grayscale.
  3. 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.
  4. Select one of the following bitmap conversion methods, and click OK:

    50% Threshold

    Converts pixels with gray values above the middle gray level (128) to white, and those below to black. The result is a very high-contrast, black-and-white representation of the image.

    50% Threshold conversion
    Original grayscale image (left) and 50% Threshold conversion method applied (right).

    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 it’s below middle gray, it’s changed 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. This option is useful for viewing images on a black-and-white screen.

    Pattern Dither and Diffusion Dither conversion methods
    Pattern Dither and Diffusion Dither conversion methods

Convert a bitmap-mode image to grayscale

Before converting, keep in mind that a bitmap-mode image edited in grayscale mode may not look the same when converted back to bitmap mode. For example, consider a pixel that is black in bitmap mode and then edited to a shade of gray in grayscale mode. If the gray value of the pixel is light enough, it will become white when converted back to bitmap mode.

  1. Choose Image > Mode > Grayscale.
  2. Enter a value from 1 to 16 for the size ratio.

    The size ratio is the factor for scaling down the image. For example, to reduce a grayscale image by 50%, enter 2 for the size ratio. If you enter a number greater than 1, the program averages multiple pixels in the bitmap-mode image to produce a single pixel in the grayscale image. This process lets you generate multiple shades of gray from an image scanned on a 1‑bit scanner.

Convert an image to indexed color

Converting to indexed color reduces the number of colors in the image to a maximum of 256—the standard number of colors supported by the GIF and PNG‑8 formats and many web browsers. This conversion reduces file size by deleting color information from the image.

Opomba:

To convert to indexed color, you must start with either a grayscale or an RGB image.

  1. Choose Image > Mode > Indexed Color.
  2. Click OK to flatten layers.

    Opomba:

    This will flatten all visible layers and discard hidden layers.

    For grayscale images, the conversion happens automatically. For RGB images, the Indexed Color dialog box appears.

  3. Select Preview in the Indexed Color dialog box to display a preview of the changes.
  4. Specify any of the following conversion options and click OK.

    Palette

    Specifies the color palette to apply to the indexed-color image. There are 10 color palettes available:

    Exact

    Creates a panel using the exact colors that appear in the RGB image—an option available only if the image uses 256 or fewer colors. Because the image’s panel contains all of the colors in the image, there is no dithering.

    System (Mac OS)

    Uses the Mac OS default 8‑bit panel, which is based on a uniform sampling of RGB colors.

    System (Windows)

    Uses the Windows system’s default 8‑bit panel, which is based on a uniform sampling of RGB colors.

    Web

    Uses the 216 colors that web browsers, regardless of platform, use to display images on a monitor limited to 256 colors. Use this option to avoid browser dither when images are viewed on a monitor display limited to 256 colors.

    Uniform

    Creates a panel by uniformly sampling colors from the RGB color cube. For example, if Photoshop Elements takes 6 evenly spaced color levels, each of red, green, and blue, the combination produces a uniform panel of 216 colors (6 cubed = 6 x 6 x 6 = 216). The total number of colors displayed in an image corresponds to the nearest perfect cube (8, 27, 64, 125, or 216) that is less than the value in the Colors text box.

    Local or Master Perceptual

    Creates a custom panel by giving priority to colors to which the human eye has greater sensitivity. Local Perceptual applies the panel to individual images; Master Perceptual applies the selected panel to multiple images (for example, for multimedia production).

    Local or Master Selective

    Creates a color table similar to the Perceptual color table, but favoring broad areas of color and the preservation of web colors. This option usually produces images with the greatest color integrity. Local Selective applies the panel to individual images; Master Selective applies the selected panel to multiple images (for example, for multimedia production).

    Local or Master Adaptive

    Creates a panel by sampling the colors from the spectrum appearing most often in the image. For example, an RGB image with only the colors green and blue produces a panel made primarily of greens and blues. Most images concentrate colors in particular areas of the spectrum. To control a panel more precisely, first select a part of the image that contains the colors you want to emphasize. Photoshop Elements weights the conversion toward these colors. Local Adaptive applies the panel to individual images; Master Adaptive applies the selected panel to multiple images (for example, for multimedia production).

    Custom

    Creates a custom panel by using the Color Table dialog box. Either edit the color table and save it for later use, or click Load to load a previously created color table. This option also displays the current Adaptive panel, which is useful for previewing the colors most often used in the image.

    Previous

    Uses the custom panel from the previous conversion, making it easy to convert several images with the same custom panel.

    Colors

    Specifies the number of colors to include in the color table (up to 256) for Uniform, Perceptual, Selective, or Adaptive panels.

    Forced

    Provides options to force the inclusion of certain colors in the color table. Black And White adds a pure black and a pure white to the color table; Primaries adds red, green, blue, cyan, magenta, yellow, black, and white; Web adds the 216 web-safe colors; and Custom lets you define custom colors to add.

    Transparency

    Specifies whether to preserve transparent areas of the image during conversion. Selecting this option adds a special index entry in the color table for a transparent color. Deselecting this option fills transparent areas with the matte color, or with white if no matte color is chosen.

    Matte

    Specifies the background color used to fill anti-aliased edges that lie adjacent to transparent areas of the image. With Transparency selected, the matte is applied to edge areas to help blend the edges into a web background of the same color. With Transparency deselected, the matte is applied to transparent areas. Choosing None for the matte creates hard-edged transparency, if Transparency is selected; otherwise, all transparent areas are filled with 100% white.

    Dither

    Specifies whether to use a dither pattern or not. Unless you’re using the Exact color table option, the color table may not contain all the colors used in the image. To simulate colors not in the color table, you can dither the colors. Dithering mixes the pixels of the available colors to simulate the missing colors.

    None

    Does not dither colors but, instead, uses the color closest to the missing color. This tends to result in sharp transitions between shades of color in the image, creating a posterized effect.

    Diffusion

    Uses an error-diffusion method that produces a less structured dither than the Pattern option. To protect colors in the image that contain entries in the color table from being dithered, select Preserve Exact Colors. This is useful for preserving fine lines and text for web images.

    Pattern

    Uses a halftone-like square pattern to simulate any colors not in the color table.

    Noise

    Helps to reduce seam patterns along the edges.

    Amount

    Specifies the percentage of image colors to dither. A higher amount dithers more colors, but may increase file size.

    Preserve Exact Colors

    Prevents colors in the image that are in the color table from being dithered.

Edit colors in an indexed-color table

You can edit colors in the color table to produce special effects, or assign transparency in the image to a single color in the table.

  1. Open the indexed-color image in Photoshop Elements.
  2. Choose Image > Mode > Color Table.
  3. Click or drag within the table to choose the color or range of colors you want to change.
  4. Choose a color from the Color Picker or sample a color from the image.

    If you are changing a range of colors, Photoshop Elements creates a gradient in the color table between the starting and ending colors. The first color you choose in the Color Picker is the beginning color in the range. When you click OK, the Color Picker reappears, so that you can choose the last color in the range.

    The colors you selected in the Color Picker are placed in the range you selected in the Color Table dialog box.

  5. Click Preview to view the results of the changes you have made to the image.
  6. Click OK in the Color Table dialog box to apply the new colors to the indexed-color image.

Assign transparency to a single color in an indexed-color table

  1. Choose Image > Mode > Color Table.
  2. Select the eyedropper, and click the desired color in the table or in the image. The sampled color is replaced with transparency in the image. Click OK.

Use a predefined indexed-color table

  1. Choose Image > Mode > Color Table.
  2. Select an option from the Table menu:

    Black Body

    Displays a panel based on the different colors a black body radiator emits as it is heated—from black to red, orange, yellow, and white.

    Grayscale

    Displays a panel based on 256 levels of gray—from black to white.

    Spectrum

    Displays a panel based on the colors produced as white light passes through a prism—from violet, blue, and green to yellow, orange, and red.

    System

    Displays the standard 256-color system panel for Mac OS or Windows.

Save or load an indexed-color table

  • To save a table, click the Save button in the Color Table dialog box.
  • To load a table, click the Load button in the Color Table dialog box. After you load a color table into an image, the colors in the image change to reflect the color positions they reference in the new color table.

Opomba:

You can also load saved color tables into the Color Swatches panel.

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