libPNGimage - a (preliminary) library for decoding & encoding PNG images

[TehSomeLuigi 5]

Today I present to you a library I have been working on: libPNGimage

The library allows you to decode and encode PNG images. Please note that at the time of writing, it is missing some features and is not therefore fully standards-compliant.

 

The library makes use of slightly-modified versions of DeflateLua and CRC32Lua by David Manura, which are both licensed under MIT.

As for libPNGimage itself, as long as you leave my little credits header there, you can do whatever you want with it .

 

I have a quick demonstration application 'pngview' which I will release to the forums shortly after this is written up.

API Functions:

PNGImage = require('libPNGimage')
 

PNGImage.newFromScratch(width: number, height: number, bkcol: table): pngimage
Creates a new pngimage object with the specified width and height. Bkcol is a table with either {R, G, B, A} or {R, G, B} to be filled onto the canvas.

PNGImage.newFromFileHandle(fh:handle): pngimage
Creates a new pngimage object by reading a PNG file from the IO file handle.

PNGImage.newFromFile(filename: string): pngimage
Creates a new pngimage object by loading the PNG file at the absolute path given.


pngimage.ihdr
is a table with IHDR data:
pngimage.ihdr.width - the width of the image

pngimage.ihdr.height - the height of the image

pngimage.ihdr.bit_depth - the bit depth of the image

pngimage.ihdr.color_type - the color type of the image
pngimage.ihdr.compression_method - the compression method of the image

pngimage.ihdr.filter_method - the filter method of the image
pngimage.ihdr.interlace_method - the interlacing method of the image
 

pngimage:getSize(): width: number, height: number
returns the width and height of the image

pngimage:getPixel(x: zerobased-number, y: zerobased-number): r: number, g: number, b: number, a: number
returns the R, G, B and A values for the pixel at the coordinates specified.
WARNING: Coordinates are zero-based i.e. they start at 0!

pngimage:setPixel(x: zerobased-number, y: zerobased-number, col: table)
sets the pixel at the coordinates specified to the colour specified. The colour is to be specified as a table of the {R, G, B, A} components.
WARNING: Coordinates are zero-based i.e. they start at 0!

pngimage:saveToFile(filename: string)
saves the image in PNG format to file using absolute file path.

pngimage:saveToFileHandle(fh: handle)
saves the image in PNG format to the IO file handle specified.

 

pngimage:lineXAB(ax: number, y: number, bx: number, col: table)
draws a line of pixels in along the X axis from (ax, y) to (bx, y).
The colour is to be specified as a table of the {R, G, B, A} components.
 

pngimage:lineYAB(x: number, ay: number, by: number, col: table)
draws a line of pixels in along the Y axis from (x, ay) to (x, by).
The colour is to be specified as a table of the {R, G, B, A} components.

 

pngimage:lineRectangleAB(ax: number, ay: number, bx:number, by: number, col: table)
draws a (non-filled) rectangle from (ax, ay) to (bx, by).
The colour is to be specified as a table of the {R, G, B, A} components.
 

pngimage:fillRectangleAB(ax: number, ay: number, bx:number, by: number, col: table)
draws a filled rectangle from (ax, ay) to (bx, by).
The colour is to be specified as a table of the {R, G, B, A} components.

 

Please note that the current version (r001) has some limitations:

• Images using Interlacing are not supported.
• Images not using Truecolour or Truecolour+Alpha colour types are not supported. This means Grayscale/Indexed images are not supported.
• Images not using bitdepth of 8 are not supported.
• When exporting, the PNG data is not compressed so it will generate files bigger than it loads. These are still PNG-compliant though.

libPNGimage-r001.zip

Also included in the download is my 'pngview' program which I have yet to write up. You can probably figure out how to use it though.

[ingie 6]

i must try this out...

 

i was wanting to do exactly this for automatically sensing a player with a motion sensor/ct radar and displaying a hologram projection of the player's skin by wrapping the png data around a hologram model...

 

i'll report back on how that works out for me

[ingie 6]

righty...

 

i've got it happily pulling down my skin and drawing it in the hologram... i just need to define a matrix of x,y -> x,y,z points to UV wrap it now...

 

i decided, since the colour depth is much lower, to use an algorithm of

    col = (r or 0) * 256 ^ 2 + (g or 0) * 256 + (b or 0)
    
    paletteindex = col == 0 and 0 or col < 0x555555 and 1 or col < 0xAAAAAA and 2 or 3

to get the index for the hologam voxel colour... 

 

seems to work ok, naturally weirdly different colours, but the contrast is right between the shades that should be there... 

 

i'll report further tomorrow i hope... 

 

 

edit: oh, screenshot or it didn't happen, i guess: [ that's my moustache over there on the right, that's what my IRL one is like, but more green, i think ] 

 

[TehSomeLuigi 5]

righty...

 

*snip*

Glad to see it's working for you and my little project will have some usage!

[ingie 6]

... one thing i think i'm noticing, the "zeroth" value in both axes seems to be missing when doing the "getPixel(x,y) ...

 

i.e. from my image above, it's missing the far left and top row of pixels...

[ and i'm just going from 0,63 x 0,31 y  and transferring that to the hologram ]

 

if i pull any pixel from x == 0 or y == 0 then i always get 0,0,0,0 back... 

the base is correct, as if i pull from row/column 1, then i DO get the correct value for column 1 [ = the 2nd row or column from base zero ] 

 

compare to my actual skin: http://s3.amazonaws.com/MinecraftSkins/ingie_.png

 

i've checked and double checked, and i can't see it as a bug in my code - as i can just loop over row 0 or column 0 and always get nothing... 

 

 

or maybe it'd be better if i didn't try and plot voxel row/column(0,1,0)  

 

damn option base 0, horrible thing. or 1, either

[ingie 6]

yup... tis working ok... i've wrapped my head around it now... literally... 

 

i just have to wrap my arms, body, legs and moustache around it....

[ingie 6]

righty... here we are then

 

https://www.dropbox.com/s/ye2lihjabxc6ic6/holoskin.lua?dl=0

 

usage is: holoskin [iGN]

 

note: by default it saves into a folder "skins" - create that or change the option at the end of the code before the main call.

 

for other options see the bottom of the code. 

 

examples

 

me:

 

 

tehsomeluigi:

 

 

sangar:

 

[TehSomeLuigi 5]

Nice work! I must play around with hologram emitters myself some time, I frankly have never even so much as placed one in the world!

If I'm honest, it's a surprise I got so far with this library -- as normally I'll start a project and never finish it to a usable state.

[pboachie 0]

I get this error whenever i run it https://www.dropbox.com/s/d1xe89xlss9qkqt/Selection_005.png?dl=0

[ingie 6]

I get this error whenever i run it https://www.dropbox.com/s/d1xe89xlss9qkqt/Selection_005.png?dl=0

 

hmm... i only had that when i got the capitalisation of the IGN wrong or the servers were being lame...

 

I just tried it and it worked fine...  do you have an internet card in the case? as - rather obviously, i guess - it needs to download the skin

if you have, then i'd just try again - i had the odd time when it just didn't but it was connection issues rather than the code itself - although I could

make it error check and try again a few times, it didn't seem worth it at this stage as my plan is to expand it into a library for further things.

 

[ingie 6]

I get this error whenever i run it https://www.dropbox.com/s/d1xe89xlss9qkqt/Selection_005.png?dl=0

 

i just thought, could be my lack of documentation in the post...

 

the download is saved to a directory names "skins" by default - you can change this in the bottom of the code... or create that folder

sorry about that.

[biswop 0]

can you make them stand up?

[Cat 3]

can you make them stand up?

Yes, you can make the images stand up. This is apparent because on some of the screenies posted there was 3D graphical output (because of the Y values changing in the blocks).

Probably some changes in the code could easily make this happen. Experiment around and tell me how it works out for you.

[MoonlightOwl 26]

 

[Daraketh 2]

What is the max resolution of a PNG image in pixels for this library?

 

Sorry if this is a stupid question, I assume it's 160x50, same as the T3 GPU's max res?

 

I'm asking as I've been playing around with it, but I'm having some trouble getting anything over 64 pixels wide to display.

 

EDIT: I'm testing images with pngview.lua

[Daraketh 2]

Hey all,

I ended up getting a PNG of 160x50 pixels and cutting it into 3 segments, 64x50, 64x50, 32x50, then stitching those together. That seems to have worked for now.

 

If anyone happens to know why I can't just use a single 160x50 png I'd love to know, particularly if I'm doing it wrong.

 

The main error I'm getting is a context error of 8, though I was also getting noeof related errors and others too.

 

Specifically the error is as below...

 

While attempting to load '/zel4.png' as PNG, libPNGImage erred:

/lib/deflatelua.lua:115: unexpected end of file with context 8

 

Cheers!

[Daraketh 2]

Turns out I need some practice reading.

 

For some reason I thought "When exporting, the PNG data is not compressed so it will generate files bigger than it loads. These are still PNG-compliant though." meant I should not use compressed PNGs

 

Works really well, thanks a lot!

[MoonlightOwl 26]

Hi, Daraketh!

I'm sorry it has taken me so long to get back to you, I've been very busy lately.

 

Maximal size for images that I have used - 160x100 px. To improve the picture quality, I used a trick with Unicode characters - half blocks (http://www.alanwood.net/unicode/block_elements.html).

 

I have modified "show" script a bit, to render images properly. Here you can find it: http://pastebin.com/UqM8dTjH

You will need "libPNGimage", "deflatelua" and "crc32lua" libs.

 

Images:

 

[Daraketh 2]

Thanks MoonlightOwl, very helpful!

[ThatSimon 0]

Hey! I've got a Question:

How do I show the images? I've got everything on the hard drive, made a 50x50 Picture for testing (test.png), I put it on my harddrive,rejoined the world started pngviewer and entered "test.png" into the field.

Then I've got the following error:

PNGView: PNG loading Error
While attempting to load '/test.png' as PNG,libPNGImage erred:
/deflatelua.lua:115: unexpected end of file with content 8

How do I fix this?

[Arimil 0]

Sounds like your deflatelua script is corrupt.

[stgX_ 0]

I get this error:

While attempting to load '/libPNG/stgX_.png' as PNG, libPNGImage erred:
too long without yielding

The resolution of the image is 161 x 66px..

Can someone help me?

[Arimil 0]

This usually means it's taking to long to load the image, you can try lowering the resolution more.

[EBSammy 0]

I am having just a bit of trouble using this plugin. I'm fairly new to OpenComputers as a whole, so please correct me if I'm wrong in any of these steps I've taken.
From the start, I:

1. got a T3 case with a T3 graphics card, 2 T2.5 RAM, and a T1 hard drive

2. installed openos on the hard drive

3. Pasted the contents of the zip file in the OP into my /lib/ folder corresponding to the hard drive

4. placed the same miku picture Moonlight used in /home/ to use as a test

5. Ran "pngview", and input "miku.png"

Similar to simon, I recieved an error:

 

* PNG Loading Error *
While attempting to load '/home/miku.png' as PNG, libPNGImage errored:
/lib/deflatelua.lua:115: unexpected end of file with context 1

Similar but not the same as mine is with the "context 1". If anyone could assist or let me know if I'm missing something, it would be greatly appreciated.

[Arimil 0]

How did you download the files to the computer? I have a feeling you got garbage html in your image.