PNGLua

A pure lua implementation of a PNG decoder

Usage

To initialize a new png image:

img = pngImage(<path to image>, newRowCallback, verbose, memSave)

The argument "verbose" should be a boolean. If true, it will print messages while decoding. The argument "memSave" should also be a boolean. If true, it will not save pixel data after it has been decoded (you must use the pixel data passed to the newRowCallback to deal with image data).The available data from the image is as follows:

img.width = 0
img.height = 0
img.depth = 0
img.colorType = 0
img.pixels = { 
                1: { 
                    1: { R: ..., G: ..., B: ..., A: ...}, 
                    2: { R: ..., G: ..., B: ..., A: ...}, 
                    ...
                },
                2: { 
                    1: { R: ..., G: ..., B: ..., A: ...}, 
                    2: { R: ..., G: ..., B: ..., A: ...}, 
                    ...
                }    
                ...            
            }

The newRowCallback argument should have the following structure:

newRowCallback(rowNum, rowTotal, rowPixels)

"rowNum" refers to the current row, "rowTotal" refers to the total number of rows in the image, and "rowPixels" refers to the table of pixels in the current row.

Support

The supported colortypes are as follows:

• Grayscale
• Truecolor
• Indexed
• Greyscale/alpha
• Truecolor/alpha

So far the module only supports 256 Colors in png-8, png-24 as well as png-32 files. and no ancillary chunks.

More than 256 colors might be supported (Bit-depths over 8) as long as they align with whole bytes. These have not been tested.

Multiple IDAT chunks of arbitrary lengths are supported. Filter type 0 is currently the only supported filter type.

Errors

So far no error-checking has been implemented. No crc32 checks are done.