From colimal at mails.selgrad.org  Thu Mar 11 17:29:21 2010
From: colimal at mails.selgrad.org (colimal at mails.selgrad.org)
Date: Thu, 11 Mar 2010 18:29:21 +0100
Subject: [cl-gd-devel] [question] change of colors when tiling an image
Message-ID: <20100311172921.GA27863@deathmetal>

Hello all :)

I'm using cl-gd to generate tiles of a larger image. I'm generating a set of
tiles of each, e.g. 256x256 pixels, from an input image that is much larger,
e.g. 4096x2048.

When using "debug-images" (pngs) with few colors and large areas of the same
color this works well. However, when I want to tile a png file with higher
frequencies and lots of colors the resulting tile images seem to be resampled
somehow, with a huge loss of quality.

Here is part of my code:

  (with-image-from-file (src input-name)
   (let ((width (image-width src))
         (height (image-height src)))

        ;; store a single tile
        (defun generate-tile (x y)
          "Generates a single tile. The index of which is given in x and y"
          (with-image (dest size size)
            (copy-image src dest (* x size) (* y size) 0 0 size size)
            (write-image-to-file (concatenate 'string output-base "-" (write-to-string x) "-" (write-to-string y) "." ext)
                                 :image dest :if-exists :supersede :compression-level 0)))
               
        ;; master's actual code
        (let ((count-x (ceiling (/ width size)))
              (count-y (ceiling (/ height size))))
             (format t "Slicing up ~s (~d x ~d) into (~d x ~d) tiles of size (~d x ~d).~%" input-name width height count-x count-y size size)
             (dotimes (x count-x)
                      (dotimes (y count-y)
                               (generate-tile x y))))))

As you can see, I don't compress the image (doesn't change, if I leave the
compression key out), and only copy a given section to the output image.
The version of cl-gd I'm using is 0.5.7, the version of is libgd 2.0.0.

I would appreciate if someone would hint me to what I'm missing :)

Thanks in advance,
   Kai.




From hans.huebner at gmail.com  Thu Mar 11 18:02:15 2010
From: hans.huebner at gmail.com (=?ISO-8859-1?Q?Hans_H=FCbner?=)
Date: Thu, 11 Mar 2010 19:02:15 +0100
Subject: [cl-gd-devel] [question] change of colors when tiling an image
In-Reply-To: <20100311172921.GA27863@deathmetal>
References: <20100311172921.GA27863@deathmetal>
Message-ID: <fd2982321003111002r2510e4d5t29eed1da25a1d9db@mail.gmail.com>

Kai,

I guess your tiles are written in palette mode.  Have a look at the
optional TRUE-COLOR-P argument that WITH-IMAGE provides.

-Hans

On Thu, Mar 11, 2010 at 18:29,  <colimal at mails.selgrad.org> wrote:
> Hello all :)
>
> I'm using cl-gd to generate tiles of a larger image. I'm generating a set of
> tiles of each, e.g. 256x256 pixels, from an input image that is much larger,
> e.g. 4096x2048.
>
> When using "debug-images" (pngs) with few colors and large areas of the same
> color this works well. However, when I want to tile a png file with higher
> frequencies and lots of colors the resulting tile images seem to be resampled
> somehow, with a huge loss of quality.
>
> Here is part of my code:
>
> ?(with-image-from-file (src input-name)
> ? (let ((width (image-width src))
> ? ? ? ? (height (image-height src)))
>
> ? ? ? ?;; store a single tile
> ? ? ? ?(defun generate-tile (x y)
> ? ? ? ? ?"Generates a single tile. The index of which is given in x and y"
> ? ? ? ? ?(with-image (dest size size)
> ? ? ? ? ? ?(copy-image src dest (* x size) (* y size) 0 0 size size)
> ? ? ? ? ? ?(write-image-to-file (concatenate 'string output-base "-" (write-to-string x) "-" (write-to-string y) "." ext)
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? :image dest :if-exists :supersede :compression-level 0)))
>
> ? ? ? ?;; master's actual code
> ? ? ? ?(let ((count-x (ceiling (/ width size)))
> ? ? ? ? ? ? ?(count-y (ceiling (/ height size))))
> ? ? ? ? ? ? (format t "Slicing up ~s (~d x ~d) into (~d x ~d) tiles of size (~d x ~d).~%" input-name width height count-x count-y size size)
> ? ? ? ? ? ? (dotimes (x count-x)
> ? ? ? ? ? ? ? ? ? ? ?(dotimes (y count-y)
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? (generate-tile x y))))))
>
> As you can see, I don't compress the image (doesn't change, if I leave the
> compression key out), and only copy a given section to the output image.
> The version of cl-gd I'm using is 0.5.7, the version of is libgd 2.0.0.
>
> I would appreciate if someone would hint me to what I'm missing :)
>
> Thanks in advance,
> ? Kai.
>
>
> _______________________________________________
> cl-gd-devel site list
> cl-gd-devel at common-lisp.net
> http://common-lisp.net/mailman/listinfo/cl-gd-devel
>



From colimal at mails.selgrad.org  Thu Mar 11 20:14:54 2010
From: colimal at mails.selgrad.org (colimal at mails.selgrad.org)
Date: Thu, 11 Mar 2010 21:14:54 +0100
Subject: [cl-gd-devel] [question] change of colors when tiling an image
In-Reply-To: <fd2982321003111002r2510e4d5t29eed1da25a1d9db@mail.gmail.com>
References: <20100311172921.GA27863@deathmetal>
	<fd2982321003111002r2510e4d5t29eed1da25a1d9db@mail.gmail.com>
Message-ID: <20100311201454.GA28952@deathmetal>

Thank you!
Should have guessed something like that... :)

Kai.


On 19:02 Thu 11 Mar     , Hans H?bner wrote:
> Kai,
> 
> I guess your tiles are written in palette mode.  Have a look at the
> optional TRUE-COLOR-P argument that WITH-IMAGE provides.
> 
> -Hans
>