colors from gif file

[marauder]

Hi. Just wondering if anyone has any idea on how to get what colors (as values)are in a gif image?

Thanks

Edited June 10, 2005 by marauder

[t0ddie]

uhmmm.. pixelgetcolor

??

oh yeah, and you can use the autoit info window

if you want them all... you will have to search the entire pic.. might take a few seconds.

Edited June 10, 2005 by t0ddie

[marauder]

Doesn't that only work for what's on the screen? I'm actually looking for something to read in an image file and get the colors.

Thanks

[buzz44]

Do you know of any other programs that can do this?

[marauder]

Actually I've just had a good look at ImageMagick again and using the 'identify' cmd with '-verbose' gives the color table of it with the histogram which it seems shows what colors are in there, so I'm going to make a script to get those colors out. Cool!

[blindwig]

do a search and find the GIF format, and write a function to read it out of the file. Shouldn't be too hard, I wrote on to do a similiar thing with BMPs ahwile back, using Pascal.

[blindwig]

do a search and find the GIF format, and write a function to read it out of the file.  Shouldn't be too hard, I wrote on to do a similiar thing with BMPs ahwile back, using Pascal.

<{POST_SNAPBACK}>

OK, I just found some documents:

http://www.dcs.ed.ac.uk/home/mxr/gfx/2d/GIF87a.txt

http://www.dcs.ed.ac.uk/home/mxr/gfx/2d/GIF89a.txt

and it looks like this is how it works:

read the 5th byte of the file.

1) Check the lowest (0) bit. If it's set to 1 then a color palette is included, otherwise not.

2) Get bits 1,2,3 and make a number out of them and add one. Raise this number to the power of 2 and this will be the scale for the strength of the color channels.

3) Get the highest 3 bits and make a number out of them and add one. Raise this to the power of 2 and you will get the number of colors in the palette.

4) Starting at the 8th byte of the file, read 1 byte per channel (RGB=3 bytes) times the number of colors given (step 3) and scale each channel according to the max value as specified in step 2

[blindwig]

...

read the 5th byte of the file.

...

4) Starting at the 8th byte of the file

...

<{POST_SNAPBACK}>

Oops, I forget the GIF header. Add 6 to those byte counts.

[blindwig]

OK, in a fit of boredom, I wrote this function:

CODE

Func _GifGetHeader($FileName)

Dim $hndFile_GIF, $aReturn[10], $OK = -1, $FileSize

;Verify that file exists and is openable

IF $OK Then

$hndFile_Gif = FileOpen($FileName, 0)

If $hndFile_Gif < 0 Then $OK = 0

EndIf

;Verify that file is the minimum size

IF $OK Then

$FileSize = FileGetSize($FileName)

If $FileSize < 13 Then $OK = 0

EndIf

;Verify that file has GIF signature header

If $OK Then

$Data = FileRead($hndFile_Gif, 3)

If not ($Data == 'GIF') Then $OK = 0

EndIf

;Read GIF image descriptor, verify filesize

If $OK Then

$aReturn[0] = 9

$Data = FileRead($hndFile_Gif, 3)

$aReturn[1] = $Data

$Data = _FileReadBin($hndFile_Gif, 7)

$aReturn[2] = $Data[2] * 256 + $Data[1] ;Width

$aReturn[3] = $Data[4] * 256 + $Data[3] ;Height

$aReturn[4] = BitShift(BitAND($Data[5], 128), 7) ;Global Color Palette

$aReturn[5] = BitShift(BitAND($Data[5], 64 + 32 + 16), 4) + 1 ;bits of color resolution

$aReturn[6] = BitShift(BitAND($Data[5], 8), 3) ;Palette is sorted most- to least-used

$aReturn[7] = BitShift(BitAND($Data[5], 1 + 2 + 4), 0) + 1 ;bits per pixel

$aReturn[8] = $Data[6] ;background color

$aReturn[9] = $Data[7] ;marker = #0

If $aReturn[9] <> 0 then $Ok = 0

If $aReturn[4] And $FileSize < 13 + (2 ^ $aReturn[7]) * 3 Then $OK = 0

EndIf

;Read Global Color Palette

If $Ok Then

$aReturn[0] = 9 + 2 ^ $aReturn[7]

Dim $i, $r ,$g, $b

ReDim $aReturn[$aReturn[0] + 1]

For $i = 1 To 2 ^ $aReturn[7]

$Data = _FileReadBin($hndFile_Gif, 3)

;scale the color values up to 255

$r = $Data[1] * 255 / (2 ^ $aReturn[5] -1)

$g = $Data[2] * 255 / (2 ^ $aReturn[5] -1)

$b = $Data[3] * 255 / (2 ^ $aReturn[5] -1)

;combine and convert to hex

$aReturn[$i+9] = Hex(($r*256+$g)*256+$b,6)

Next

EndIf

;Close file handle

FileClose($hndFile_Gif)

;Return gathered data

If $OK Then

Return $aReturn

Else

SetError(1)

Return ''

EndIf

EndFunc

It calls my _FileReadBin() function and returns an array:

element 0=number of elements returned

element 1=GIF version

element 2=width

element 3=height

element 4=color table encluded

element 5=color resolution

element 6=Palette is sorted by color usage

element 7=bits per pixel

element 8=background color

element 9=reserved

element 10...=color in 0xRRGGBB format