When making realistic looking sprites or large images for use with OpenRCT2, dithering is the best solution.

Wikipedia: Dither is an intentionally applied form of noise used to randomize quantization error, preventing large-scale patterns such as color banding in images.

To dither images for OpenRCT2, two general approaches can be taken.

The sprite compiler that converts images to be used in game has options to automatically dither the images. For more information see the sprite compiler documentation.

The first image has no palette. The second image is using the RCT2 palette with no dithering. The third image is using the RCT2 palette with dithering.

• Photoshop (the previewed version is CS6)
• Another tool for editing images with transparency (such as Paint.NET, if you're not already skilled with Photoshop)
• RCT2 Pal files (found below)

• With Water - This should be used for any image being drawn in the intro scene, title screen, rollercoaster designer, or track manager as they will never have a different water palette.

• Without Water - This should be used for any image being drawn in a scenario or the scenario editor since the water palette may be different.

• Download the RCT2 pal files.
• Open up your image in Photoshop.
• Transparency needs to be used for the background, otherwise the edges of the image won't look right after being converted.
• If the edges of your image are (or are close to) pure white, you may have a problem when adding transparency to your image.

• Goto Image > Mode > Indexed Color....

• The Indexed Color window will pop up.
• Open the Palette drop-down and select Custom....

• The Color Table window will pop up.
• Click Load to open one of the two pal files you downloaded earlier.
• In the Files of type drop-down select Microsoft Palette(R) (.Pal) and then locate the RCT2 pal file.

• Now you can color your image using dithering.
• You can change the Amount percentage between 1%-100% however somewhere around 50% usually looks best. The image will update as you change the value.
• Click OK when you're done.

• Now you have your image with the correct palette, but there's no transparency.
• I've found adding transparency with Photoshop is more complicated than just using another image editor. So if you know how to do it in Photoshop then go ahead.
• Copy the entire image and paste it in your alternative image editor.
• Next fill in the white background with transparency. This is where problems may occur if the edges of your image were already white.

• And you're done. Save the image in the resources/g2 directory as a numbered png and you're good to go.