Image Format dialog

The Image Format dialog is opened in the Image/Animations editor to set the file format for an image when the project is exported.

Images in the project are always saved in PNG-32 format. This is the only format that exactly preserves an image with an alpha channel. The settings here are only used when the project is exported. They are mainly used to reduce the image file sizes so the game download is smaller.

Images in either PNG format are also recompressed on export to further reduce the filesize without affecting the image quality. For more information on the recompression techniques Construct 2 uses on export, see this blog post on Image compression in Construct 2.

The Image Format dialog has the following options:

Format

The format of the image when exported. In brief, the formats are as follows:
PNG-32 (default) can store true color images losslessly (perfectly, without any quality loss) with full alpha channel transparency. However, it usually also produces the largest file.
PNG-8 is a 256-color version of PNG. It supports alpha channel transparency, but within the 256 colors only. Retro or low-color images should look exactly the same in PNG-8. Images with more than 256 colors have to be reduced to only 256 colors which can degrade the image quality. However, Construct 2 uses an advanced dithering algorithm (PNGNQ) to achieve this color reduction. This means many images still look almost identical. PNG-8 files are also often much smaller than PNG-32 files, so using PNG-8 is a useful way to reduce the download size of the game.
JPEG is an image format designed for photographic or highly detailed images. It does not support transparency at all, so it is not suitable for images which have any transparent areas or alpha channels (they will appear as if on a black background). However, JPEG can achieve the smallest files of all, depending on the quality setting. This is generally best for minimising the size of large background images.
For more information on these formats see the Wikipedia articles on PNG and JPEG.

Quality

The quality setting when using the JPEG format. JPEG quality ranges from 0 (worst quality, smallest file) to 100 (best quality, largest file). Quality settings above 85 are often difficult to distinguish from the original. 75 is recommended as a compromise between quality and reducing the file size as much as possible.

Apply this setting to

Allows you to set the same image format for many images at once. This frame or This image applies the image format only to the currently viewed image or animation frame. This animation (Sprite only) applies the image format to all the frames in the current animation. All animations (Sprite only) applies the image format to the entire object - all its frames in all its animations. Entire project applies the image format to every single image in the entire project. Use this with care, since it overwrites every single other object's image format settings, and cannot be undone.