Viewing histograms

You can view a histogram for any one of the channels in your image, including alpha and spot channels, or a composite of all the modal color channels. By default, the histogram is based on the entire image,but you can view a segment by making a selection.Here is a list of the different views and how to access them:

• To view an Expanded or Compact palette,choose an option from the palette menu.
• To view all channels, choose All Channels View from the palette menu.
• To view channels in color, choose Show Channels in Color from the palette menu.
• To view channels in color and compact mode,view in Expanded mode, select Colors from the Channels pop-up, and then select Compact View from the palette menu.
• To view individual channels in Expanded View, choose an option from the pop-up menu for Channel (the pop-up is available only in Expanded View).
• To view statistics,choose an option from the palette menu (by default, statistics are displayed in the Expanded View and All Channels View).
• To view a histogram based on the current layer, choose an option from the pop-up menu for Source.

When the histogram is based on cached data instead of the document’s current state, a yellow warning triangle appears (the cache level is specified in the Preferences➜Memory & Image Cache).You have a number of options at your disposal for displaying a histogram based on the document’s current state. You can:

• Double-click anywhere on the histogram.
• Click the cached data-warning icon (Figure 3-19).
• In expanded view,click the “Uncached Refresh”button at the top of the palette(Figure 3-20).
• Choose Uncached Refresh from the Histogram palette menu.

When viewing histograms, keep in mind that a bad histogram, that is, one that looks like a comb, doesn’t necessarily mean that you have a bad image. Chances are it will print just fine if the missing “teeth” aren’t wide enough to cover several missing levels. If the gaps are too wide—say, bridging three or four levels—then posterization will occur.

-- by Shangara Singh

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