Compress4

gistfile1.txt

--# ReadMe

--[[
First, don't be put off by all this text. This utility is extremely simple to use.

It creates code that reproduces images so you don't need to include them separately with your projects. It uses RLE, a well known compression technique. Essentially, it runs through all the pixels, and every time the color changes, it stores the last color and the number of pixels it applied to.

FUNCTIONALITY
It can turn any image(with reason) into code strings, and reassemble the image from them.

It can take images from the libraries, and convert to compressed code.

The practical limits on image size and complexity are processing speed and storage, because the greater the number of colors and pixels, the more space we have to allow for each item. 

FUNCTIONS
The Coder:Encode function takes the image as input and saves the code in the ImageCode tab to recreate it. You copy this code to your project. 
    
Important - the Imagecode tab will look very strange because the Codea editor can't display very long lines of code. Just copy the whole tab anyway.
    
Note, you will also need to copy the Decoder tab to your project.
   
Usage: Coder:Encode(img)  --then copy and paste the printed code 
    
NB As well as printing the code, the Coder function also returns the two strings required to decode the image. This is only for testing purposes, so the Main tab can show how it works - in practice, you will just copy the printed code and not worry about the return values.

The Decoder:Decode function takes two strings as input and returns an image. Normally, you don't have to worry about this because the printed code calls the function correctly for you, returning the image.

The Main function carries out several tests
It reads in an image from the standard library, codes and then decodes it back to an image
It takes an image previously created by this code, and encodes/decodes it back to an image

USING IT
Only the ImageCoder tab is needed to encode images

Only the Decoder tab needs to be included in any project where you want to decode RLE images.

COMPRESSION
The level of compression depends on many factors, but the code generated by this project between not much greater than the original image size for simpler (few colour) images, up to about double, for complex images.

Dermot (user:Ignatz)
--]]


--# Main
-- Compress
function setup()
    --Read image from library
    --You can pick any image you like, but don't make it too big or complex
    img1 = readImage("Small World:Icon")
    saveImage("Dropbox:Cute",img1)
    --Normally, you only need to run the single line of code below, which prints the code you need
    --The function does return two strings, but you can ignore them (they are just for testing), 
    --just copy what is printed out in the Output screen, and and paste it into your own project
    --So normally, you'll just run Coder:Encode(img1)
    --The Test tab shows how it looks when pasted in, and that is the third example below
    local strCol,str=Coder:Encode(img1)
    --The rest of the code below is just to prove it works
    --check we can reproduce the original image we loaded above, using the compressed code
    img_new1=Decoder:Decode(img1.width,img1.height,strCol,str)
    print("Alongside is the original image and the result after encoding and decoding it")
    print("The total size of the code is about ",#strCol+#str.." chars")
    if img then print("On the right is the image whose code is stored in the Imagecode tab. It may not be the same image as on the left, if you've just changed that image") end
end

function draw()
    background(208, 208, 214, 255)
    
    text( "This utility converts images to code you can embed in your project", 290, 550 )
    text( "Library original", 100, 500 )
    sprite(img1,100,400)
    text( "Copy from code", 100, 250 )
    sprite(img_new1,100,150)
    --if we've previously saved an image to code, decode and show it
    if img then 
        text("Image from Tab",300,250)
        sprite(img,300,150)       
    end
end





--# Coder
Coder = class()

--This function encodes an image in two strings
--the first string makes a list of unique color settings (r,g,b,a), encoded as an 8 char hex string
--the second string runs through the image, through rows then columns, and every time the color changes,
--it records the color setting and number of cells that had that color
--NB it doesn't store the color setting as an 8 char hex string, imstead it stores the position of
--this color in the first string. This saves a lot of storage where colors are used over and over again

Codes="!#&~*+,)/0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ]_`abcdefghijklmnopqrstuvwxyz"
--     1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678
--              1         2         3         4         5         6         7         8   

function Coder:Encode(img)
    local rows=img.height
    local cols=img.width 
    local colors={} --hash table of unique colors, gives us their sequence in the unique list
    local strCol="" --unique list of color settings, each one is 8 chars hex, for r,g,b,a
    local str=""  -- each item consists of a color setting (or rather, the position in strCol), and the number of
            --cells to be colored
    --for example, if the image starts with 56 cells with r=1,g=2,b=5,a=6, we will add the hex value of this,
    --which is 001002005006, to strCol, and set colors[001002005006]=1, (1 because this is the first color)
    --to str, we add the hex values of the string position, ie 1, and the number of cells, ie 56, so we will
    --add 001038 to str  
    local colorCount=0
    local prevColor=-1 --to tell us when the color changes
    local count=0 --number of cells with current color
    local r,g,b,a,x
    local tbl={}
    local tblCol={}
    --loop through image
    for i=1,cols do
        for j=1,rows do
            r,g,b,a=img:get(i,j)
            x=r..","..g..","..b..","..a
            if x==prevColor then
                count=count+1
            else --color has changed, store details of last color
                if count>0 then --this will only be zero for the very first cell
                    y=colors[prevColor] --this looks up the position of the color, in the color list
                    if y==nil then --add the color to the list if not there
                        colorCount = colorCount + 1
                        y=colorCount
                        colors[prevColor]=colorCount
                        --if colorCount>1 then 
                            --table.insert(tblCol,","..prevColor)
                        --else
                            table.insert(tblCol,prevColor)
                        --end
                    end  
                    table.insert(tbl,y..","..count)
                end
                prevColor=x
                count=1
            end
            if errMessage~=nil then break end     
        end 
        if errMessage~=nil then break end
    end
    --we've finished, but we may have some left over chars that need to be stored
    if count>0 then
        y=colors[prevColor]
        if y==nil then
            colorCount = colorCount + 1
            colors[prevColor]=colorCount
            y=colorCount
        end
        table.insert(tblCol,y)
        table.insert(tbl,count)
    end
    str=table.concat(tbl,",")
    strCol=table.concat(tblCol,",")
    --create code for user
    if errMessage~=nil then 
        print(errMessage)
        return errMessage,errMessage
    else
        str1=Coder:Compress(strCol)
        str2=Coder:Compress(str)
        Coder:PrintCode(cols,rows,str1,str2)   
        return str1,str2
    end    
end
    
function Coder:Compress(d)
    local a={}
    local m=0
    local y,z
    local x=string.gsub(d,"8","82")
    x=string.gsub(x,"7","81")
    x=string.gsub(x,"9","83")
    x=string.gsub(x,",","7")
    for i=1,#x,2 do
        y=string.sub(x,i,i)*9
        if i<#x then y=y+string.sub(x,i+1,i+1) else y=y+7 end
        y=y+1
        z=string.sub(Codes,y,y)
        table.insert(a,z)
    end
    return table.concat(a)
end


function Coder:PrintCode(c,r,s1,s2)
   saveProjectTab("ImageCode","--image code\nimg=Decoder:Decode("..c..","..r..",'"..s1.."','"..s2.."')")
end


--# Decoder
Decoder=class()

Codes="!#&~*+,)/0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ]_`abcdefghijklmnopqrstuvwxyz"
--     1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678
--              1         2         3         4         5         6         7         8   

function Decoder:Decode(cols,rows,cc,dd)
    local img=image(cols,rows)
    local n=0
    local m=4
    local arrCols={}
    strCol=Decoder:Decompress(cc)
    strDat=Decoder:Decompress(dd)
    --unpack color descriptions
    for q in string.gmatch(strCol,"[^,]+") do
        m = m + 1
        if m==5 then 
            m=1
            n = n + 1
            arrCols[n]={}
        end
        arrCols[n][m]=q
    end
    --if m~=4 then print("faulty column codes, m=",m) end
    --unpack RLE content
    local col=1
    local row=0
    local ind=1
    n=0
    for q in string.gmatch(strDat, "[^,]+") do
        if ind==1 then 
            colIndex=tonumber(q) 
        else
            colCount=tonumber(q)
            n = n + 1
            for u=1,colCount do
                row = row + 1
                if row>rows then col=col+1 row=1 end
                img:set(col,row,
            color(arrCols[colIndex][1],arrCols[colIndex][2],arrCols[colIndex][3],arrCols[colIndex][4]))
            end
        end 
        ind=3-ind  
    end
    return img
end

function Decoder:Decompress(a)
    local s={}
    local d1,d2,y,x
    for i=1,#a do
        y=string.find(Codes,string.sub(a,i,i))-1
        d2=y%9
        d1=(y-d2)/9
        d2=d2
        table.insert(s,d1)
        table.insert(s,d2)
    end
    if s[#s]==7 then table.remove(s,#s) end
    str=table.concat(s)
    x=string.gsub(str,"7",",")
    x=string.gsub(x,"81","7")  
    x=string.gsub(x,"83","9")
    x=string.gsub(x,"82","8") 
    return x
end