Introduction to Indexed Pixel Art in GIMP (Graphical Image Manipulation Program)
GIMP as a graphics editor
A major frustration to me was finding the way to change the colour, or view swatches or rgb values from the default user interface.
So it took a period of investigation to accumulate the knowledge to actually find and choose colours to be used in brushes and fills.
Basic functions can be confusing and the default layout can serve as a barrier, as it’s arranged with no particular use in mind. There is no way to load in preset workspaces in recent version, so the first thing is to understand the tabs (Dockable Dialogues) you need to work with.
Setting up the Workspace for Pixel Art
First we will customise the tabs.
Tip: You can switch from single-window mode to floating-window mode from either checking or unchecking Window > Single-Window Mode.
I tend to use single-window mode as I find it can get messy working in floating-window mode.
When you switch from floating to single-window, floating tabs islands will attempt to retain their relative positions within the sidebar, where they will nest automatically.
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Toolbox Window including sidebar Docked Mode arranges your tabs automatically when changing from Floating window mode. |
First set up the Toolbox Window. Go to Edit > Settings > Interface > Toolbox.
Go to Window Management and make sure Window Manager Hints are set to ‘Normal window’. This will show descriptions for most interface objects as well as in menu dialogues.
In Tools Configuration, remove all but the Rectangle Select Tool (R), Move Tool (M), Text Tool (T), Color Picker Tool (O) and Zoom Tool (Z).
Then remove the GIMP mascot image to save more space.
Tip: If you wish to choose a different tool icon size Go to Icon Theme in settings (above Toolbox) and click "Guess icon size from resolution" drop down box and choose "Custom icon size" to choose from four sizes from Small to Huge.
Toolbar / Sidebar Palettes and Tabs
First remove all of the tabs chosen for the default workspace.
Below the tools in the Toolbox Window, put a line of tabs.
Go to Windows > Dockable Dialogs > ... to create new tabs, which you can then drag into existing palette tab group windows, or to make new tab windows, which can be arranged in columns and vertically adjacent.
Also, you can use Add Tab from an existing tab group with the ‘configure tab’ icon in the top right corner of a palette window.
Add the tabs Navagation, Color, Tool Options and Palettes in that order for just 4 tabs beneath the toolbox. This makes it easier to remember where the tabs are, as the icons are very small and easy to confuse if you have too many.
Tip: Use Tab Style (configure tab icon, top right) and select “Icon” for your tabs, to save space.
Make a new tab group below the first group, with the tabs, Layers and Undo history with ‘text and icon’ style tabs to make the tab header’s bigger. Experiment with additional tabs and layouts if you like.
Tab windows/dockable dialogues don’t seem to be able to shrink below a certain point. In Single-Window Mode, the Toolbar bar won’t go very narrow.
I tend to leave the Toolbox (tool icons) Window/Sidebar open with tabs attached to it and arrange other tabs around it as needed such as a Palettes tab and Palette Editor tab. I might do this in floating window mode as tab groups in the sidebar cannot be resized horizontally, individually.
Be aware, if you close the toolbox you lose all tab layouts within the toolbar window. But you could make them again without the Toolobox if you don’t feel you need the tool buttons to always be visible.
Tip: When changing from floating to Single-Window Mode, your window positions will approximate into the docked Toolbox sidebar.
Working With Colour
You can view the currently selected colour, foreground colour and background colour from the Color tab with RGB, hex information, colour history swatches, colour spaces and indexes if your image is indexed.
If you select the Color Picker Tool (O), in Tool Options, check Layer Info Window to display RGB and hex colour information in the image window.
If the Color Picker tool is set to foreground or background colour, the related index swatch will be highlighted in the Palette Editor.
Tip: RGB values are arranged in six hexidecimal values as 00 - ff for red, green and blue, consecutively. #00ff00 is pure green. #808080 is mid grey. HSV (Hue, Saturation, Value) values aren’t useful here.
The Pencil Tool (N) will draw 1 pixel at a time if you set it to 1 pixel from Tool Options or you can use brushes, but with the limited palettes of pixel art, we won’t be using it here as we aim for 15 colours a tile, in, for instance, a 32x32 pixel area.
Fill the layer or selection with ‘ctrl+,’ or ‘ctrl+.’ or Edit > Fill with FG Color, BG Color.
Colour Palettes
Colour palettes are organised alphabetically in the Palettes tab.
The Palette Editor shows the colour indexes in colour swatches. To open the Palette Editor, double click a palette, or click the palette configuration button > Palettes Menu > Edit Palette.
When you have the Palette Editor open, arrange it to the left of the toolbar window. Then add a Palette tab above or below, as you probably don’t need the whole horizontal space for swatches. The palettes tab changes the editor swatches displayed, dependant one which is selected.
Clicking once on a swatch brings up colour information in the Color tab or you can double click it to open the Color dialogue window where you can also edit the values.
Tip: I tend to have my palette preview size set to Large in the Palettes tab, which fits 7 into the space and displays about 80 swatches per palette. Changing the preview size won’t change the swatch size. You can view the palettes as a grid from tab configuration button > View as Grid, I prefer to see the names of the palettes and name them, so leave it on View as List.
Palette editor and selecting values
Edit the number of columns in your palette editor swatch layout with the numbers in the lower right hand side of the Palette Editor window and adjust their height with the buttons below it.
Tip: I tend resize my swatches into squares and rows of of 8 or 16 columns to get larger swatch sizes. But changing the amount of columns sometimes helps to group shades together. 4 rows will allow you to compare and reduce reduce tone sets to rows of , for instance. This way you can discard unnecessary swatches until you have groups of tones arranged visually.
Scanned illustration showing Palette Editor and Palettes tabs in docked view with Gradient tab open
To add colours to your selected palette, go to Color Picker tool (O), go to tool options and select add to palette. The new swatch will then appear in the selected colour palette.
You can’t arrange swatches within the palette editor window but you can drag a swatch onto another swatch to duplicate it next to the designation swatch, then delete the original swatch. It’s not ideal.
To generate a palette from an image go to Image > Mode > Indexed and select the amount of colours you require, up to 256. This generates a new palette in the palettes tab list, named Colormap of Image [image name] #N, which you might want to duplicate and rename as it will disappear once the window is closed. The number of indexes is displayed in brackets after the name in the palette list.
Indexed 8bit colour image with 256 index colormap and image information shown
Pasting and Layers
One of the first things you need to understand is how layers work. They have boundaries, distinct from the canvas size (final exported image dimensions) and the working area (very large).
You paste in from the clipboard in different ways.
The fastest is to simply go to Edit > Paste (ctrl-v). But you just created a new Floating Selection and not a new layer.
The next required step is to turn the ‘floating selection‘ into a new layer, file, or ‘anchor’ it to an existing layer.
From the floating selection, go to Layer > To New Layer (shift-ctrl-n) or clicking the green New Layer button from the Layer tab. Or Anchor the floating selection, potentially overwriting existing content in that layer with Layer > Anchor Layer (ctrl+h) or the button, which will be highlighted in green at this point.
You can merge two layers with Layers > Merge Down or the button in the layer tab (third from right).
Once it is a layer, your pasted image will become editable.
You might prefer to go to Edit > ‘Paste as’, then choose to paste into selection or into a new file. Now you can work with the image you pasted from the clipboard. You might want to rename your layers or put them in groups.
Canvas Size and Dimensions
To expand your canvas size to the dimensions of the layers, if they exceed it, go to Image > Fit Canvas to Layers.
To reduce the layer boundaries (distinct from canvas size) to the layer’s content, go to Layer > Crop to Content.
To reduce the canvas size to all the content, removing blank space from the boundaries, go to Image > Crop to Content. Crop to the selection with Image > Crop to Selection.
The Image menu refers to all layers. Canvas size is the dimensions of your image, viewed with Image > Image Information. The Layers menu concerns individual layer transforms.
If you cannot draw onto the canvas, you may need to increase your layer size to the boundaries of the working area with Layer > Layer to Image Size.
Viewing
The image viewing window doesn’t have arrows on the scroll bars so I tend to drag the image with them for smaller movements in the viewing area in the image window.
However, there are many other ways.
Hold the space bar (if no selection box is selected) and move the cursor to pan with the hand tool to pan the view area.
Another way is to click the arrow icon in the bottom right hand corner of the image window to pan the view area.
Or you can use the Navigator panel (small north-facing arrow) by clicking and dragging within the preview window. The zoom buttons at the bottom of the Navigator tab give you zoom in or out, 1:1 pixels or fit to window (left to right).
Tip: I like to use the navigator preview window to judge the sprite at a size which might be closer to the display sizes.
Alternatively, the Zoom Tool will zoom in with left-click and out with left-click+ctrl. Drag an area with zoom tool to resize to the window.
The + and - keys also zoom in and out. The + key needs you to press shift as well. 1- 5 zooms between 100% and 1600%.
Selection Box
When using the selection box, dragging again inside the box will move the selection box. The transparent squares in the corners or dragging from the edges will resize it.
You can add, subtract or intersect with the Tool Option tab (double-click the tool or select Tool Option tab).
Ctrl+shift+a or clicking outside the selection box deselects. Clicking inside the selection box hides the resize boxes.
There are tools for working with layer masks but they aren't covered here.
Layers
When a layer is selected, the layer content is actually selected and the copy command will copy the contents of the layer, including obstructed areas outside the canvas area into clipboard memory.
You can toggle layer outlines with View > Show Layer Boundary.
To scale the layer and reduce a pixel art image, retaining colour values, go to Layer > Scale Layer and set interpolation to None.
Tip: Use only values that retain square pixels such as 50% or 200%. Calculate using doubles or halving pixel values to avoid aliasing and losing colour values or square pixels.
You cannot edit content beyond the layer boundaries, so you might want to go to Layer > Layer to Image Size.
To reduce your layer boundary down to only the content, go to Layer > Layer to Content size.
Tip: If you have clicked on a tab or outside the image window, you will need to click on the layer again in the image window to move it with the cursor keys and Move Tool (M). The move tool will select whichever layer is beneath the cursor when moving layers.
The Eraser tool (shift+E) only has a binary value, so it can only remove the pixel completely from the layer, using the brush shape which is useful in pixel art.
If you require to erase with a gradient and wide alpha channel bits, you will need to enable a mask layer within your layer by right clicking and clicking Add Layer Mask. With the layer mask selected, choose a black brush to achieve a smooth gradient when erasing pixels from a layer.
The Pencil tool (n) set to 1px will draw only solid opaque pixels.
Move Layer
Choose the Move tool (M) and drag within any visible pixels on the layer to move the layer. To move the layer without clicking onto visible pixels go to tool options (double click to tool in the Tool Palette) and check Move Layer then Tool Toggle (shift) "Move the active layer" radio button.
To move the pixels within a selection make a selection from the selection tools or converting from a layer mask or path layer, or with a rectangle selection box (R) selected, cut the pixel (ctrl+x) and then paste onto a new layer (ctrl+alt+v), deselect the selection box and then use the move tool again, with move layer selected and drag or use the cursor keys.
Effects
You might not need many effects, as working in pixel art tends to be hand drawn, a single pixel at a time or from a scan with adjustments.
Now you’re ready to start using GIMP and understand it’s unique working method of content, layers, layer boundaries and canvas boundaries and to navigate it’s interface.
Gradient Map Duotone Filter
In order to apply a duotone effect to your image, first select the correct layer, then select your foreground and background colour in the Color tab. Then go to the menu: Colors > Map > Gradient Map and the filter will be applied. Swapping the foreground and background colors (X) will reverse the filter.
The filter blends the foreground colour to the background colour taking the luminance values from darkest to highest using the selected foreground colour as the darkest point and averaging the colours over the gradient to the background colour, being the lightest point.
The Color > Map > Palette Map filter takes the order of the selected palette from the first entry as the darkest point, taking each consecutive index in a consistent graduated amount with the last colour in the palette list used for the lightest value.
Scanned illustration showing Palette Editor and Palettes tabs in docked view with Gradient tab open
Export
To save your image to publish on the web, or send go to File > Export. You might want to choose PNG for general viewing for compression with little loss of quality.
For photographs or illustration use jpg.
For pixel art use gif, which will use indexed colour and save space without losing detail for images up to 256 colours.
Choose File > Export as... and choose a folder and filename.
To save over the exported file with changes, simply press Export.
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