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Re^5: About GD Image Data Output Methods

by BrowserUk (Patriarch)
on Jun 07, 2015 at 20:13 UTC ( [id://1129374] : note . print w/replies, xml ) Need Help??


in reply to Re^4: About GD Image Data Output Methods
in thread About GD Image Data Output Methods [SOLVED]

Hm. Both versions work with my image viewer. Can you make a copy of your image available to me in .gd & the converted format? Or attach them to an email to me?

Are you using truecolor images?


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Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
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Re^6: About GD Image Data Output Methods
by karlgoethebier (Abbot) on Jun 07, 2015 at 21:01 UTC

    Do'h! Know it works. GD::Image->trueColor(1); did it.

    And convert mandelbrot.bmp mandelbrot.png works too.

    Thank you very much for advice and best regards, Karl

    P.S.: If you can effort the time it would be very nice to get some explanations about how your code works. I guess that only a few understand it just by inspection. Unfortunately i'm not one of the chosen. But i'm working on it ;-)

    «The Crux of the Biscuit is the Apostrophe»

      some explanations about how your code works.

      Both formats are very simple, uncompressed files, with almost the same data format; which makes conversion simpler.

      I detailed the gd format header in Re: About GD Image Data Output Methods.

      I used this for the bmp format details.

      Hopefully these comments will explain the rest.

      ## Get the gd format data as a string my $gd = $image->gd; ## Unpack the header (we're only interested in the width & height) and + strip that header from the image data my( undef, $width, $height, undef, undef ) = unpack 'nnnCV', substr( $ +gd, 0, 11, '' ); ## GD image data is 4 bytes (rgba); BMP image data is 3 bytes; so calu +late the length the bmp image data with occupy my $len = length( $gd ) / 4 * 3; ## Pack the required information to create a .bmp header (in two parts +). (see link above) my $bmp = pack 'a2 V V V l< l< l< v v V V l< l< V V', ## The .bmp file header has 5 fields (but 2 U16s do nothing so pack 1x +U32 value 0 for them) ## sig file-length (data+header length), 2 unused shorts as U32, an +d the offset to the rgb data. 'BM', $len + 54, 0, 54, ## BITMAPINFOHEADER 40 bytes, image width & height (negative to turn i +t the right way up!), ## color planes (1), bits/pel(24), compression type(none:0), length of + rgb data, 3 unused fields. 40, $width, -$height, 1, 24, 0, $len, 0, 0, 0; ## Convert the rgba gd data to rgb bmp data (x skips the alpha bytes) ## And tack it onto the end of the header. $bmp .= join'', unpack '(xaaa)*', $gd;

      Of course, the code is crude as .bmps have a multitude of other possibilities, and (as you've seen) I don't even check for truecolor .v. palette in the gd format; but the intention was to give you something that did the job, not duplicate the functionality of image conversion software.

      It wouldn't be too hard to handle palette images; but I don't think it is necessary for your purpose.


      With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority". I'm with torvalds on this
      In the absence of evidence, opinion is indistinguishable from prejudice. Agile (and TDD) debunked

        Thank you very much for your explanation.

        Best regards, Karl

        «The Crux of the Biscuit is the Apostrophe»