2.2. Kanaldialogen

Figur 15.7. Kanaldialogen

Kanaldialogen

Kanaldialogen er staden du bruker for å utføre arbeid direkte på kanalane, både å redigere og gjere andre endringar. Kanalane vert brukte på to måtar. Det er difor dialogen er delt i to. Den første delen er for fargekanalar og den andre for utvalsmasker.

Color channels apply to the image and not to a specific layer. Basically, three primary colors are necessary to render all the wide range of natural colors. As other digital software, GIMP uses Red, Green, and Blue as primary colors. The first and primary channels display the Red, Green, and Blue values of each pixel in your image.

Next to the channel name is a thumbnail displaying a grayscale representation of each channel, where white is 100% and black is 0% of the primary color. Alternatively, if your image is not a colored but a Grayscale image, there is only one primary channel called Gray. For an Indexed image with a fixed number of known colors there is also only one primary channel called Indexed.

Then there is an optional channel called Alpha. This channel displays transparency values of each pixel in your image (See Alpha Channel in Glossary). In front of this channel is a thumbnail displaying a grayscale representation of the transparency where white is opaque and visible, and black is transparent and invisible. If you create your image without transparency then the Alpha channel is not present, but you can add it from the Layers dialog menu. Also, if you have more than one layer in your image, GIMP automatically creates an Alpha channel.

[Notat] Notat

GIMP har ikkje støtte for fargemodellane CMYK og YUV

Figur 15.8. Biletkomposisjon med kanalar

Biletkomposisjon med kanalar

Raudkanal

Biletkomposisjon med kanalar

Grønkanal

Biletkomposisjon med kanalar

Blåkanal

Biletkomposisjon med kanalar

Alfakanal

Biletkomposisjon med kanalar

Alle kanalane


Biletet heilt til høgre er sett saman av dei fire kanalane, raud, grøn, blå og alfa. Sjakkbrettmønsteret viser gjennomsiktige område. Sidan kvit farge i den brukte fargemodellen er sett saman av alle primærfagane, vil kvit vere kvitfarga (100 %) i alle kanalane. Svart er mangel på farge, og vil difor visast som svart (0 %) i alle kanalane. Den raude hatten er synleg i raudkanalen, men ikkje i dei andre. Dette gjeld for alle reine grøne eller blå fargar også. Dei er berre synlege i respektive kanalar.

2.2.1. Aktivering

Dette er ein dialog som kan limast inn i andre dialogvindauge. Sjå nærare om dette i Del 2.3, «Dialogar og samlevindauge («dokker»)».

Du har tilgang til dialogvindauget

  • from the main menu: WindowsDockable DialogsChannels;

  • from the Tab menu in any dockable dialog by clicking on and selecting Add TabChannels.

In the Windows menu, there is a list of detached windows which exists only if at least one dialog remains open. In this case, you can raise the «Channels» dialog from the main menu: WindowsChannels.

2.2.2. Using the Channels dialog

2.2.2.1. Oversyn

The channels at the top are the color channels and the optional Alpha channel. They are always organized in the same order and they cannot be removed. In the middle are two lock buttons, that show the lock status for the currently selected channel in the bottom area. The bottom area shows a list of selection masks. Every channel appears in the list with its attributes, including a thumbnail and its name. A right-click in a channel list entry opens the channel context menu.

2.2.2.2. Channel lock attributes

Above the list of selection mask channels are two check boxes that show the lock attributes state of the currently selected mask channel.

Lås pikslar

The paintbrush icon shows whether «lock pixels» is enabled (highlighted) for the current channel. When this is enabled, the channel is locked for any action that changes the pixels, meaning there will be no changes done to this channel.

Lås plassering og storleik

The cross-with-arrows icon shows whether «lock position and size» is enabled (highlighted) for the current channel. When this is enabled, the channel is locked for any action that changes the position or size.

2.2.2.3. Kanaleigenskapane

Kvar kanal vert vist i lista saman med attributta for kanalen. Dette er nokså likt det som er brukt for lagattributta:

Endra elementvisinga

I utgangspunktet er alle kanalane, og såleis også alle fargane, synlege. Dette vert vist med eit augesymbol. Klikk på symbolet for å slå av maska, eller på den tomme plassen for å slå maska på.

Lenk saman kanalar

The channels representing selection masks (in the lower part of the channel list) may be grouped using the button with the «chain» symbol. All channels that have the chain enabled will be affected in the same way by operations applied to any one of them.

Primary color channels (the default channels in the upper part of the channel list) may be grouped too. By default, all color channels (and the alpha channel) are selected, their list entries are highlighted. Operations will be performed on all channels. By clicking on a channel list entry you can deactivate this channel. Operations like colorizing a layer will then be applied to the selected («grouped») channels only. Clicking on the deactivated list entry will activate the channel again.

Miniatyr

A small preview icon represents the effect of the channel. This preview can be enlarged by holding down the left mouse button on it.

Kanalnamn

The name of the channel, which must be unique within the image. Double-clicking on the name of a selection mask channel will allow you to edit it. The names of the primary channels (Red, Green, Blue, Alpha) can not be changed. Double-clicking on the preview icon will open a dialog where you can set all channel attributes.

[Obs] Obs

Activated channels appear highlighted in the dialog. If you click on a channel in the list you toggle activation of the corresponding channel. Disabling a color channel red, blue, or green has severe consequences. For instance if you disable the blue channel, all pixels from now on added to the image will not have a blue component, and so a white pixel will have the yellow complementary color.

2.2.2.4. Handtering av kanalane

Below the channel list is a set of buttons allowing you to perform some basic operations on channel list.

Ny kanal

This creates a new channel. A dialog will open where you can set the Channel name, the Color tag, the channel attributes and lock attributes, and finally the Opacity and color used for the mask in the image window. A click on the color button displays the GIMP color selector where you can change the mask color. If you press the Shift key while clicking the New Channel button, the New Channel Dialog will not be opened. Instead the new channel will be created with the same settings as used previously. This new channel is a channel mask (a selection mask) applied over the image. See Selection Mask

Raise Channels

Only available for selection masks: this moves the selected channels up in the list. Press Shift key to move the channel to the top of the list.

Lower Channels

This moves selected channels down in the list. Press the Shift key to move the channel to the bottom of the list.

Duplicate Channels

This creates a copy of the active channels. The name of the new channel is suffixed with a number.

[Tips] Tips

You can also duplicate color channels or the Alpha channel. It's an easy way to keep a copy of them and to use them later as a selection in an image.

Replace the Selection with Selected Channels

This transforms the selected channel to become a selection. By default the selection derived from channels replaces the active selection. You can change this by using control keys.

  • Shift: the selection derived from a channel is added to the active selection. The final selection is merged from both.

  • Ctrl: the final selection is the subtraction of the selection derived from a channel from the active selection.

  • Shift+Ctrl: the final selection is the intersection of the selection derived from a channel with the active one. Only the selected parts common to both are kept.

Delete Channels

Only available for selection masks: this deletes the selected channels.

2.2.2.5. Lokalmenyen kanalar

Figur 15.9. Kanalmenyen

Kanalmenyen

Oversyn

You can get the channel context menu by right clicking on a channel. Several of the operations on channels are also available through buttons at the bottom of the channels list. Those operations are documented there.

New Channel…, Raise Channels, Lower Channels, Duplicate Channels, Delete Channels

Sjå kanalhandtering.

Edit Channel Attributes…

Only available for selection masks. Here you can change the Channel name, the Color tag, the channel attributes and lock attributes, and finally the Opacity and color used for the mask in the image window. A click on the color button displays the GIMP color selector where you can change the mask color.

Color Tags

Only available for selection masks. This allows you to assign a color tag to a channel. If you have a lot of channels this can make it easier to identify them by giving related channels the same color tag. To remove the color tag choose None.

Channels to Selection

The selection derived from a channel replaces the previously active selection.

Add Channels to Selection

The selection derived from a channel is added to the active selection. The final selection is merged from both.

Subtract Channels from Selection

The final selection is the subtraction of the selection derived from a channel from the active selection.

Intersect Channels with Selection

The final selection is the intersection of the selection derived from a channel with the active one. Only the selected parts common to both are kept.

2.2.3. Utvalsmasker

Figur 15.10. Eit utval laga av kanalar

Eit utval laga av kanalar

Du kan bruke kanalar for å lagre og henta fram igjen utval. I kanaldialogen kan du sjå ein miniatyr som viser utvalet. Utvalsmaskene er ein metode for lage utvalet om til ein gråskalakanal der kvite punkt er utvalde og svarte punkt ikkje er utvalde. Grå punkt er delvis utvalde. Du kan sjå på desse som ein mjuk overgang frå utvalde til ikkje utvalde område. Dette er viktig for å unngå den stygge «pikseleringseffekten» (hakkete overgangar) som kan oppstå når du fyller utvalet med farge eller bruker viskeleret på utvalet.

Å opprette utvalsmasker

Utvalsmaska kan aktiverast på fleire måtar.

  • From the main menu SelectSave to Channel if there is an active selection.

  • In the image window the bottom-left button creates a Quick Mask; the content will be initialized with the active selection.

  • Frå kanaldialogen når du trykker på knappen Ny kanal eller frå lokalmenyen. Når utvalsmaska er oppretta, vert ho synleg i kanaldialogen med namnet «Ny kanal», eventuelt med eit tal dersom det er fleire kopiar. Du kan endre namnet ved å høgreklikka på kanalen.

2.2.3.1. Å bruke utvalsmasker

Once the channel is initialized, selected (highlighted in blue), visible (eye-icon in the dialog), and displayed as you want (color and opacity attributes), you can start to work with all the paint tools. The colors used are important. If you paint with some color other than white, gray, or black, the color Value (luminosity) will be used to define a gray (medium, light, or dark). When your mask is painted, you can transform it to a selection by clicking on the button (Channel to Selection) or from the context menu.

Du kan arbeide på utvalsmaska med andre verktøy enn teikneverktøya. For eksempel kan du bruke utvalsverktøya for å fylle eit område av maska med fargeovergangar eller mønsterelement. Det er såleis mogleg å komponera svært komplekse utval ved å kombinera ulike utvalsmasker.

[Obs] Obs

Så lenge utvalsmaska er aktiv, arbeider du på denne og ikkje på biletet. Skal du arbeide på biletet, må du deaktivere alle utvalsmaskene. Gløym heller ikkje å skjule maskene ved å klikke på augeikonet. Det er også ein god ide å kontrollera at alle RGB- og alfakanalane er aktiverte og vert viste i biletet.

2.2.4. Snarmaske

Figur 15.11. Dialogen for Snarmaske

Dialogen for Snarmaske

A Quick Mask is a Selection Mask intended to be used temporarily to paint a selection. Temporarily means that, unlike a normal selection mask, it will be deleted from the channel list after its transformation to selection. The selection tools sometimes show their limits when they have to be used for doing complex drawing selection, as progressive. In this case, using the Quick Mask is a good idea which can give very good results.

2.2.4.1. Aktivering

The Quick Mask can be activated in different ways:

  • From the main menu: SelectToggle Quick Mask.

  • ved å klikke på den vesle knappen nede i venstre hjørne av biletvindauget, som vist på skjermbiletet

  • eller med tastesnarvegen Shift + Q.

2.2.4.2. Å lage ei snarmaske

For å setja opp Snarmaske klikkar du på knappen nede til venstre i biletvindauget. Dersom det finst eit aktivt utval i biletet, vil dette vere uforandra, men alt rundt vert dekka av ein raud, gjennomsiktig film. Dersom biletet ikkje har noko utval, vert heile biletet dekka med filmen. Klikk ein gong til på knappen for å slå av snarmaska.

From the channel dialog you can double click on the name or the thumbnail to edit the QMask attributes. Then you can change the Opacity and its filling color. At every moment you can hide the mask by clicking on the eye icon in front of the QMask.

Maska bruker gråtoner, så du må bruka kvitt eller grått for å minske området eller svart for å gjere området større. Område som er teikna med mørk eller lys grå vert omformingsområda for mjuke kantar i utvalet. Når maska er ferdig, klikk ein gong til på knappen nede til venstre i biletet for å fjerna snarmaska frå kanallista og gjera ho om til eit utval.

Føremålet med snarmaska er å kunne bruke teikneverktøya for å markere utval og overgangar utan å bry seg med utvalsmaska. Snarmaska er ein god måte å isolere eit objekt i eit bilete fordi når utvalet er gjort, kan du berre fjerne innhaldet, eventuelt etter å ha invertert maska dersom objektet er inne i markeringa.

2.2.4.3. Å bruke snarmaske med ein fargeovergang

Beskriving

  1. Screenshot of the image window with activated Quick Mask. As long as the Quick Mask is activated, all operations are done on it. A gradient from black (left) to white (right) has been applied to the mask.

  2. The Quick Mask is now disabled. The selection occupies the right half part of the image (marching ants) because the limit of the selection is at the middle of the gradient.

  3. Det vert nå påført eit strøk i det tilgjengeleg utvalet. Underleg! Sjølv om fargeovergamgen ikkje er synleg, er han nå aktiv over heile biletet, både i markerte og umarkerte område!

After the Quick Mask Button is pressed, the command generates a temporary 8-bit (0-255) channel, on which the progressive selection work is stored. If a selection is already present the mask is initialized with the content of the selection. Once Quick Mask has been activated, the image is covered by a red semi-transparent veil. This one represents the non-selected pixels. Any paint tool can be used to create the selection on the Quick Mask. They should use only grayscale color, conforming the channel properties, white enabling to define the future selected place. The selection will be displayed as soon as the Quick Mask will be toggled but its temporary channel will not be available anymore.

[Tips] Tips

To save in a channel the selection done with the Quick Mask select in the main menu SelectSave to Channel.

2.2.4.4. Bruk
  1. Opna eit bilete, eller lag eit Nytt.

  2. Activate the Quick Mask using the left-bottom button in the image window. If a selection is present the mask is initialized with the content of the selection.

  3. Choose a drawing tool and use it with grayscale colors on the Quick Mask.

  4. Deactivate the Quick Mask using the left-bottom button in the image window.