Photoshop – Channels

Channels Palette Alpha Channel

In photoshop Channels store an image’s color information. In addition to color channel, you can use alpha channels to create and store masks, which let you manipulate, isolate, and protect specific parts of an image (Alpha channels store selections as 8-bit grayscale images and are added to the color channels in an image). You can also add spot color channels to an image to let you specify additional plates for printing with spot color inks. An image can have up to 24 channels, including all color and alpha channels. All channels are 8-bit grayscale images, capable of displaying 256 levels of gray.

photoshop Channels Palette Color information channels are created automatically when you open a new image. For example, an RGB image has three default channels: one for each of the red, green, and blue colors plus a composite channel (RGB) used for editing the image.

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The Channels palette lets you create and manage channels and monitor the effects of editing. To Open the channels pallet choose Windows > Show Channels. The palette lists all channels in the image. A composite channel first (for RGB, CMYK, and Lab images), then individual color channels, spot color channels, and finally alpha channels. Appearing to the left of the channel name, a thumbnail of the channel’s contents automatically updates as you edit the channel.

To Show/Hide a channel: Click in the eye column next to the channel to show or hide that channel.

To select a channel: Click the channel name. Shift-click to select (or deselect) multiple channels. The names of all selected, or active, channels are highlighted. When a channel is visible, an eye icon appears to its left. Editing changes apply to the active channels.

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To edit a channel: Use a painting or editing tool to paint in the image. Paint with white to add to the channel; paint with black to remove from the channel; paint with a lower opacity or a color to add to the channel with lower opacities.

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Duplicating channels: You can duplicate any channel within or between images. (For example, duplicate an image’s channels to make a backup before editing the channel. Or duplicate alpha channels to a new image also to create a library of selections that you can load into the current image one by one—thus keeping the file smaller.). You can duplicate a channel using the Duplicate command OR duplicate a channel by dragging.

To duplicate a channel using the Duplicate command:
• In the Channels palette, select the channel to duplicate.
• Choose Duplicate Channel from the Channels palette menu.
• Type a name for the duplicate channel.
• For Document, do one of the following:
1 Choose a destination. To duplicate the channel in the same file, select the channel’s current file.
2 Choose New to copy the channel to a new image (creating a multichannel image containing a single channel), type a name for the new image.
• To reverse the selected and masked areas in the duplicate channel, select Invert.
• Click OK.

To duplicate a channel by dragging:
• In the Channels palette, select the channel you want to duplicate.
• To duplicate a channel within an image, drag the channel into the image window or onto the New Channel button at the bottom of the palette.
• To duplicate the channel into another image, make sure that the destination image is open. Then drag the channel into the destination image window.

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Deleting channels: Complex alpha channels can substantially increase the disk space required for an image. So you may want to delete alpha channels you no longer need before saving an image. When deleting a channel from a file with layers, photoshop prompts you first to flatten the visible layers and discard hidden layers (if any) before deleting the channel. This is necessary because removing a color channel converts the image to Multichannel mode, which does not support layers.

To delete a channel with no confirmation: Select the channel in the Channels palette and then do one of the following:
• Alt-click the Trash button ( photoshop trash)
• Drag the channel name in the palette to the Trash button.
• Choose Delete Channel from the Channels palette menu.

To delete a channel with confirmation: Select the channel in the Channels palette and then click the Trash button at the bottom of the palette. Then click Yes.

To hide/change the size of channel thumbnails: Choose Palette Options from the Channels palette menu and select a display option.
• Click a thumbnail size. (Smaller thumbnails reduce the space required by the Channels palette—helpful when you’re working on smaller monitors).
• Click None to turn off the display of thumbnails.

Click OK.

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Alpha channels: In Photoshop, masks let you isolate and protect areas of an image as you apply color changes, filters, or other effects to the rest of the image. When you select part of an image, the area that is not selected is “masked” or protected from editing. In addition, you can save and reuse time-consuming selections as alpha channels. Alpha channels can be converted to selections and then used for image editing.

An alpha channel has these properties:

• Each image can contain up to 24 channels, including all color and alpha channels.
• All channels are 8-bit grayscale images, capable of displaying 256 levels of gray.
• You can add and delete alpha channels.
• You can specify a name, color, mask option, and opacity for each channel.
• All new channels have the same dimensions and number of pixels as the original image.
• You can edit the mask in an alpha channel using the painting and editing tools.
• Storing selections in alpha channels makes the selections permanent, so that they can be used again in the same image or in a different image.

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Creating and saving alpha channels: You create a new alpha channel as a mask. Or you can save a selection to either a new or existing alpha channel.

(1) To create a new alpha channel using current options:

Click the New Channel button (photoshop alpha channels) at the bottom of the Channels palette. The new channel is named according to the sequence in which it was created.

photoshop alpha channels

(2) To create a new alpha channel and specify options:

• Either Alt-click the New Channel button (photoshop alpha channels) at the bottom of the palette OR choose New Channel from the Channels palette menu.
• Type a name for the channel.
• Select display options for the channel.
• Click OK. A new channel appears at the bottom of the Channels palette and is the only channel visible in the image window.

(3) To save a selection to a new channel with default options:

• Select the area or areas of the image that you want to isolate.
• Click the Save Selection button (photoshop alpha channels) at the bottom of the Channels palette. A new channel appears, named according to the sequence in which it was created.

(4) To save a selection to a new or existing channel:

• Select the area or areas of the image that you want to isolate and choose Select > Save Selection.

photoshop alpha channels photoshop alpha channels

• For Document, choose a destination image for the selection. (By default, the selection is placed in a channel in your active image). You can choose to save the selection to a channel in another open image with the same pixel dimensions or to a new image.

• Choose a destination channel for the selection. By default, the selection is saved in a new channel. You can choose to save the selection to any existing channel in the selected image or to a layer mask if the image contains layers.

• If you’re saving the selection to an existing channel, select how to combine the selections:
(1) Replace Channel to replace the current selection in the channel.
(2) Add to Channel to add the selection to the current channel contents.
(3) Subtract from Channel to delete the selection from the channel contents.
(4) Intersect with Channel to keep the areas of the new selection that intersect with the channel contents.

• Click OK. A new channel appears, named according to the sequence in which it was created.

• Select the channel in the Channels palette to see the saved selection displayed in grayscale.

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Loading a selection into an image You can load a previously saved selection into an image.

To load a saved selection into an image:

• Choose Select > Load Selection.
• For Document, the active filename is selected.
• For Channel, choose the channel containing the selection you want to load.
• Click Invert to make the nonselected areas selected and vice versa.
• If the destination image already has a selection, indicate how to combine the selections.
• Click OK to load the selection.

OR

• Select the alpha channel, click the Load Selection button (photoshop alpha channels) at the bottom of the palette, and then click the composite color channel near the top of the palette.

To load a selection from another image:

• Open the two images you want to use.(Note: The images must have identical pixel dimensions.)
• Make the destination image active, and choose Select > Load Selection.
• For Document, choose the source image.
• For Channel, choose the channel containing the selection you want to use as a mask.
• Click Invert if you want to make the nonselected areas selected and vice versa.
• If the destination image already has a selection, indicate how to combine the selections.
• Click OK to load the selection.

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To edit an alpha channel: Use a painting or editing tool to paint in the image. Paint with black to add to the channel; paint with white to remove from the channel; paint with a lower opacity or a color to add to the channel with lower opacities.

To change options for a channel:

• Select the channel in the Channels palette, and choose Channel Options from the palette menu.
• Enter a new name for the channel.
• Choose display options. Note: You cannot modify options for the default color channels.

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