If you click on the tabbed folder marked Channels next to Layers, you'll get closer acquainted with the wonderful world of RGB- and Alpha Channels.
When you open the Channels dialog, you'll see the three RGB-channels. Each channel represents the Red, Green or Blue color value of the pixels in your image. Think of the RGB channels as grayscale representations, where"white" is replaced with 100% color. Pure red in the red channel is the equivalent of a red value of 255 for that pixel, black means that the pixel has no red in it at all. As opposed to Layers, the RGB channels are all active at the same time. The RGB channels are also equipped with eye icons, so you can choose to watch your image in a single color channel. If you want to, you can choose just to work in one or two specific color channels, by clicking at them (click at an active channel and it becomes inactive, and vice versa).
Normally, there isn't much use in working directly in the color channels. If you are very skilled, and like to experiment with patterns and advanced coloring, this can be of interest though. You can for instance erase or add parts to the red channel, or try a filter on the blue channel etc. Just remember that the channel operation only affects the active layer. Also note that you can't use the standard edit functions like cut/copy/paste in a single RGB-channel. Moving selections in a color channel is also not possible without moving the content of all three RGB channels. If you want to do any of these things, use the Compose/Decompose option in the Image/Channel Ops menu.
No, the real reason to use the Channels dialog is that you can store and edit selections in Alpha Channels! Whenever you make a selection which is more complex than a square - save it! You are most probably going to need it later.
The Alpha value describes the amount of transparency in a pixel. Just as each pixel has a value for the Red, Green and Blue channels in the RGB system, it also has an Alpha value. Check this out with the Color Picker! As with the RGB-channels, pixel values in an Alpha channel range from 0 to 255. The max value (255) refers to 100% opaque, and 0 means totally transparent. When you create a new Channel, you create a mask which can be translated to an Alpha selection and be applied to a layer. These channels are always grayscale images (you can use colors, but they will appear as shades of gray in the channel). Black represents transparent and white opaque, the grayscale in between represents different levels of transparency.
In the Select menu there is an option called Save to Channel. When you have made a selection, choose the Save to Channel option, and open the Channels dialog. You'll find that you now have a new channel called Selection Mask copy. The channel is a grayscale version of the selection you just made. Don't forget to name the channel - this is important, because selections stored in channels aren't always easily recognized. To name the channel, double-click its old name, and a dialog box appears. Name the new channel saucer shadow or whatever your selection represents (or will represent when you have edited it). You can set a fill opacity value in the popup dialog box, but that doesn't affect the alpha values in your channel. The reason you set the fill opacity to a transparent value is that this enables you to see your image through the black parts of the channel. If this was not the case, it would be impossible to edit the channel properly.
When you want to use the selection you just stored, click the right mouse button on the channel's name, and the Channels menu appears. Choose the last option on the drop down list called Channel to Selection. This option creates a selection based on your channel - just switch to the Layers folder and your selection is ready for use!
The Channels menu should be easy to understand. You can create a new channel, raise or lower your channels, duplicate or delete them and change them into selections. You can't merge channels, unless you first copy them and paste them into layers. You can merge those layers with the merge visible layers command, then you copy or cut the layer and paste it into a channel again. As you see, the contents of alpha channels and layers can be edited just as an in ordinary images. You can paste an image or a layer into an alpha channel, and vice versa. You can paint, adjust image values, make selections or use filters on Alpha channels. This makes Channels the most powerful tool for creating advanced selections there is!
We have already discussed the fact that you can change the name and fill opacity value in the Channel pop up dialog box, but you can also change the mask color of an alpha channel. Note that setting another color than black will not turn your alpha channel into a regular color channel like the RGB channels. The RGB channels use an additional color model, where maximum color in all three channels equals white. Alpha channels however, can be compared to grayscale layers in Multiply mode. White areas are transparent, gray areas are more or less transparent and black areas are totally opaque. ![Extracted pic [1]](channels-image-1.jpeg)
usr/doc/gimp-manual/html/channels.html 100644 0 0 57036 6550011726 16404 0 ustar root root
If you click on the tabbed folder marked Channels next to Layers, you'll get closer acquainted with the wonderful world of RGB- and Alpha Channels.
When you open the Channels dialog, you'll see the three RGB-channels. Each channel represents the Red, Green or Blue color value of the pixels in your image. Think of the RGB channels as grayscale representations, where"white" is replaced with 100% color. Pure red in the red channel is the equivalent of a red value of 255 for that pixel, black means that the pixel has no red in it at all. As opposed to Layers, the RGB channels are all active at the same time. The RGB channels are also equipped with eye icons, so you can choose to watch your image in a single color channel. If you want to, you can choose just to work in one or two specific color channels, by clicking at them (click at an active channel and it becomes inactive, and vice versa).
Normally, there isn't much use in working directly in the color channels. If you are very skilled, and like to experiment with patterns and advanced coloring, this can be of interest though. You can for instance erase or add parts to the red channel, or try a filter on the blue channel etc. Just remember that the channel operation only affects the active layer. Also note that you can't use the standard edit functions like cut/copy/paste in a single RGB-channel. Moving selections in a color channel is also not possible without moving the content of all three RGB channels. If you want to do any of these things, use the Compose/Decompose option in the Image/Channel Ops menu.
No, the real reason to use the Channels dialog is that you can store and edit selections in Alpha Channels! Whenever you make a selection which is more complex than a square - save it! You are most probably going to need it later.
The Alpha value describes the amount of transparency in a pixel. Just as each pixel has a value for the Red, Green and Blue channels in the RGB system, it also has an Alpha value. Check this out with the Color Picker! As with the RGB-channels, pixel values in an Alpha channel range from 0 to 255. The max value (255) refers to 100% opaque, and 0 means totally transparent. When you create a new Channel, you create a mask which can be translated to an Alpha selection and be applied to a layer. These channels are always grayscale images (you can use colors, but they will appear as shades of gray in the channel). Black represents transparent and white opaque, the grayscale in between represents different levels of transparency.
In the Select menu there is an option called Save to Channel. When you have made a selection, choose the Save to Channel option, and open the Channels dialog. You'll find that you now have a new channel called Selection Mask copy. The channel is a grayscale version of the selection you just made. Don't forget to name the channel - this is important, because selections stored in channels aren't always easily recognized. To name the channel, double-click its old name, and a dialog box appears. Name the new channel saucer shadow or whatever your selection represents (or will represent when you have edited it). You can set a fill opacity value in the popup dialog box, but that doesn't affect the alpha values in your channel. The reason you set the fill opacity to a transparent value is that this enables you to see your image through the black parts of the channel. If this was not the case, it would be impossible to edit the channel properly.
When you want to use the selection you just stored, click the right mouse button on the channel's name, and the Channels menu appears. Choose the last option on the drop down list called Channel to Selection. This option creates a selection based on your channel - just switch to the Layers folder and your selection is ready for use!
The Channels menu should be easy to understand. You can create a new channel, raise or lower your channels, duplicate or delete them and change them into selections. You can't merge channels, unless