adding pngdec

micropython/modules/picographics/README.md

@@ -583,3 +583,42 @@ The arguments for `decode` are as follows:
 2. Decode Y
 3. Flags - one of `JPEG_SCALE_FULL`, `JPEG_SCALE_HALF`, `JPEG_SCALE_QUARTER` or `JPEG_SCALE_EIGHTH`
 4. If you want to turn off dither altogether, try `dither=False`. This is useful if you want to [pre-dither your images](https://ditherit.com/) or for artsy posterization effects.
+
+### PNG Files
+
+We've included BitBank's PNGDEC - https://github.com/bitbank2/PNGDEC - so you can display PNG files on your LCDs.
+
+Eg:
+
+```python
+import picographics
+import pngdec
+
+display = PicoGraphics(display=DISPLAY_PICO_DISPLAY, pen_type=PEN_RGB332)
+
+# Create a new PNG decoder for our PicoGraphics
+png = pngdec.PNG(display)
+
+# Open the PNG file
+png.open_file("filename.jpeg")
+
+# Decode the PNG
+png.decode(0, 0)
+
+# Display the result
+display.update()
+```
+
+PNG files must be small enough to load into RAM for decoding.
+
+PNGDEC Supports the following PNG types:
+
+1. True Colour
+2. True Colour (with Alpha)
+3. Indexed
+4. Grayscale
+
+The arguments for `decode` are as follows:
+
+1. Decode X - where to place the decoded JPEG on screen
+2. Decode Y