[cl-pdf-devel] png image representation

[Marc Battyani]

"Thibault Langlois" <tl at di.fc.ul.pt> wrote:

> On 5/30/07, iso at localhost.di.fc.ul.pt <iso at localhost.di.fc.ul.pt> wrote:
>>
>> Maybe you don't need PNG for that. If you have a vector of pixel
>> values, then just use something like this:
>>
>> (defun my-image (pixels width height)
>>   (let ((image (make-instance 'pdf:image
>>                  :color-space "DeviceCMYK"
>>                  :filter nil
>>                  :bits pixels
>>                  :width width
>>                  :height height)))
>>     (pdf:add-images-to-page image)
>>     (pdf:paint-image image)))

Yes I think it's probably easier than going through a png.


> Each pixel in the imago format is a unsigned 32bits that
> represents R, G, B and Alpha channel.
>
>> This assumes that you want to use colour separations and that the
>> dimensions of the pixel vector are (* width height 4). If you
>> have a grayscale image, then use DeviceGray instead of DeviceCMYK. Of
>
> Each pixel in the imago format is a unsigned 32bits that
> represents R, G, B and Alpha channel.
>
>> course, you can also use DeviceRGB (then the pixel vector should look
>> like this: R00 G00 B00 R01 G01 B01 ..., where R01 is the Red value of
>> the pixel at row 0 column 1).
>
> I tried to follow your suggestion using a DeviceRGB.
> First I got an error when the :bits argument is a vector of
> bytes. Looking at the code it seems that this argument must
> be a string (the data is passed to a pdf-stream and then to the
> compress-pdf-stream function where compress-string is called).
>
> So I converted each byte into a char to build a string. I do not
> get any errors but the image does not appear in the document.
>
> (defun image-example-1 (&optional (file #P"/home/tl/Desktop/ex.pdf"))
>  (pdf:with-document ()
>    (let* ((imago-image ;; Load an image as a imago:rgb-image
>            (imago:read-png "/home/tl/Photos/lemon-slice.png"))
>           (pdf-image ;; make a pdf-image using image data
>            (make-instance 'pdf:image
>                           :color-space "DeviceRGB"
>                           :filter nil
>                           :bits (string-of-bytes imago-image)
>                           :width (imago:image-width imago-image)
>                           :height (imago:image-height imago-image))))
>      (pdf:with-page (:bounds (vector 0 0 400 300))
>        (pdf:add-images-to-page pdf-image)
>        (pdf:draw-image pdf-image 10 100 250 120 0 t)
>        (pdf:write-document file)))))
>
> The string-of-bytes function collect the r g b components and
> build a string:
> (defun string-of-bytes (imago-rgb-image)
>  (let (color-values)
>    (imago:do-image-pixels (imago-rgb-image c x y)
>      (setq color-values
>            (nconc color-values
>                   (list (code-char (imago:color-red c))
>                         (code-char (imago:color-green c))
>                         (code-char (imago:color-blue c))))))
>    (coerce color-values 'string)))
>
> My first attempt was to make a vector:
>
> (defun vector-of-bytes (imago-rgb-image)
>  (let (color-values)
>    (imago:do-image-pixels (imago-rgb-image c x y)
>      (setq color-values
>            (nconc color-values
>                   (list (imago:color-red c)
>                         (imago:color-green c)
>                         (imago:color-blue c)))))
>    (coerce color-values 'vector)))
>
> Any help will be appreciated.

Have you looked at example3 in examples.lisp? It creates an in memory image 
that is put into the pdf.

Marc