PNG
Gimp can load and save PNG (Portable Network Graphics) files. ### Saving PNG files Gimp will automatically choose a type of PNG file appropriate to the image you are saving. All applications which can handle PNG files should be able to read any PNG saved from Gimp. ### Parameter Settings #### Interlacing (Adam7) The Adam7 interlacing option stores image data in an order which allows browsers or viewers to show progressively more detail as they load the file, at the cost of increased file size. #### Save background color This adds a bKGD chunk to your PNG file which advises viewer software to choose a background color like your currently selected Gimp background color. Adding this chunk increases file size slightly. #### Save gamma This adds a gAMA chunk to your PNG file which reflects the current Gamma factor for your display (set globally for Gimp). Viewers with a different display can compensate to ensure the image doesn't look too dark or too bright. Adding this chunk increases file size slightly. #### Save layer offset If you are saving a single layer which has been shifted (offset) from the top-left of the image, this will add a oFFs chunk to your PNG file to preserve this offset factor in other viewers. Adding this chunk if it's needed increases file size slightly. #### Save resolution This adds a pHYs chunk to your PNG which records the physical resolution of the image. This is needed by Gimp and other viewers for printing or actual size previews. Adding this chunk increases file size slightly. #### Save creation time This adds a tIME chunk to your PNG which records the exact date and time when the image was last saved. This will be preserved and can be viewed in other applications. Adding this chunk increases file size slightly. #### Compression This controls the amount of compression used to reduce the file size. Larger numbers will usually reduce file size but will make saving slower. The default (6) is often an acceptable compromise, but see below. On the web, size isn't everything but it is important. I suggest that finished web graphics should be saved with level 9 compression and without bKGD, oFFs, pHYs and tIME chunks. For large web graphics, like maps and diagrams, you should consider using Adam7 interlacing. For simple icons or logos, try converting with Image/Mode/Indexed... before saving. ### Loading PNG files This plug-in loads all known PNG files with following restrictions: 16 bit per channel data is reduced to 8 bit precision. Transparency in paletted images is preserved but may not be properly displayed. Image/Mode/RGB will display the full transparency. These restrictions will be addressed in a future version of Gimp. Index