ZPNG is a Common Lisp library for creating PNG files. It uses Salza2 for compression. The latest version is 1.2.1, released on November 30th, 2011.
ZPNG provides three interfaces creating PNG files. The first is through a PNG object, which holds all image sample data and which may be written out to a file all at once. The second is through a STREAMED-PNG object, which writes a single output row of the image at a time. By working with only a single row at a time, images that are too big to fit in memory may still be written out incrementally as a PNG file. The third is through a PIXEL-STREAMED-PNG object which allows you to write a single pixel at a time. It still buffers a whole row at a time, but it manages all of the buffer handling for you.
The PNG file format has many options, and ZPNG supports only a subset of them.
(defun draw-mandelbrot (file) (let* ((png (make-instance 'png :color-type :grayscale-alpha :width 200 :height 200)) (image (data-array png)) (max 255)) (dotimes (y 200 (write-png png file)) (dotimes (x 200) (let ((c (complex (- (/ x 100.0) 1.5) (- (/ y 100.0) 1.0))) (z (complex 0.0 0.0)) (iteration 0)) (loop (setf z (+ (* z z) c)) (incf iteration) (cond ((< 4 (abs z)) (setf (aref image y x 1) iteration) (return)) ((= iteration max) (setf (aref image y x 1) 255) (return)))))))))
(defun draw-rgb (file) (let ((png (make-instance 'pixel-streamed-png :color-type :truecolor-alpha :width 200 :height 200))) (with-open-file (stream file :direction :output :if-exists :supersede :if-does-not-exist :create :element-type '(unsigned-byte 8)) (start-png png stream) (loop for a from 38 to 255 by 31 do (loop for b from 10 to 255 by 10 do (loop for g from 38 to 255 by 31 do (loop for r from 10 to 255 by 10 do (write-pixel (list r g b a) png))))) (finish-png png))))
The following symbols are exported from the ZPNG package.
samples-per-pixel png => samples
Returns the number of octet samples that make up a single pixel.
Image Color Type Samples per Pixel Grayscale 1 Truecolor 3 Grayscale with Alpha 2 Truecolor with Alpha 4
width png => width
height png => height
Returns the width or height of png.
rowstride png => rowstride
Returns the number of samples in a single row of png. It is equivalent to (* (width png) (samples-per-pixel png)).
color-type png => color-type
Returns the color type of png, one of of :grayscale, :truecolor, :grayscale-alpha, or :truecolor-alpha.
Instances of this class may be created directly. Supported initargs:
- :width - required, the width of the image
- :height - required, the height of the image
- :color-type - optional, the color type of the image, one of :grayscale, :truecolor (the default), :grayscale-alpha, or :truecolor-alpha
- :image-data - optional, the sample data of the image. If specified, this must be an octet vector with a length of width × height × samples-per-pixel. If not specified, an image data vector of the appropriate size will be created automatically.
image-data png => octet-vector
Returns the image data of png. Samples are laid out from left to right, top to bottom, so the first samples of data affect the upper-left of the image and the final samples affect the lower-right.
Image Color Type Pixel Sample Layout Grayscale S|S|S... Truecolor RGB|RGB|RGB... Grayscale with Alpha SA|SA|SA... Truecolor with Alpha RGBA|RGBA|RGBA...
Layout of the samples into pixels is done according to the image's color type and is fully documented in the Portable Network Graphics Specification.
data-array png => data-array
Returns a multidimensional array representing the pixels of png. The dimensions correspond to the height, width, and pixel components, respectively. For example, to access the red component at <53,100> of a truecolor PNG, you could use this:(aref (data-array png) 100 53 0)
Note the reversed order of the coordinate arguments; this is a consequence of Common Lisp's row-major ordering of elements in a multidimensional array and PNG's specified sample layout.
copy-png png => png-copy
Create a copy of png.
png= png1 png2 => boolean
Returns true if png1 and png2 are equal. Equality is defined as having the same dimensions, color type, and image data.
write-png png file &key (if-exists :supersede) => pathname
Writes png to file and returns the truename of file. if-exists is passed to the underlying CL:OPEN call for opening the output file.
write-png-stream png stream => |
Writes png to stream, which should be an output stream that can accept octets.
Instances of this class may be created directly. Supports all the initargs of the PNG class except :IMAGE-DATA.
In contrast to PNG instances, STREAMED-PNG instances do not keep all the image data in one large vector. Instead, instances are used to write out the image data of a PNG file one row at a time. The protocol for incrementally writing out via a STREAMED-PNG involves these generic functions:
row-data streamed-png => octet-vector
Returns a vector suitable for passing to WRITE-ROW for streamed-png; it has the appropriate number of entries for the image width and color type of the png. The initial contents are all zeroes. For a given streamed png, each call to row-data will return the same vector, not a fresh one.
start-png png stream => png
Writes PNG file header data to stream, which must be an output stream that supports writing (unsigned-byte 8) data. The header data is taken from png, which must be a STREAMED-PNG instance.
write-row row png &key (start 0) end => |
Writes row to the output stream of png. row must be an (unsigned-byte 8) vector with the appropriate number of entries for png. start defaults to 0 and end defaults to start + ROWSTRIDE. The difference between end and start should be equal to (rowstride png). png must be a STREAMED-PNG instance.
If the row length, as defined by start and end, is not the right size, an error of type INVALID-ROW-LENGTH is signaled.
If writing row would exceed the number of rows in the image (as defined by HEIGHT), an error of type TOO-MANY-ROWS is signaled.
rows-written streamed-png => count
Returns the number of rows written to streamed-png so far.
rows-left streamed-png => count
Returns the number of rows left to write to streamed-png. Equivalent to (- (height png) (rows-written png)).
finish-png streamed-png => |
Concludes writing PNG file data to the output stream of streamed-png. The internal state of streamed-png is reset in such a way that it can be re-used to write another PNG file, with the same dimensions and color type parameters, using another START-PNG/WRITE-ROW/FINISH-PNG sequence.
This function must be called only after exactly HEIGHT rows have been written to streamed-png via WRITE-ROW. If too few rows have been written to streamed-png, an error of type INSUFFICIENT-ROWS is signaled.
Instances of this class may be created directly. Supports all the initargs of the STREAMED-PNG class.
The PIXEL-STREAMED-PNG class extends the STREAMED-PNG class. Rather than preparing a row of pixels and caling the WRITE-ROW method, with PIXEL-STREAMED-PNG instances, you write a single pixel at a time with the WRITE-PIXEL method. The protocol for incrementally writing out via a PIXEL-STREAMED-PNG involves these generic functions:
write-pixel pixel-samples pixel-streamed-png
Writes the samples for a single pixel from the sequence pixel-samples to the next available spot in the ROW-DATA buffer. When the buffer is full, this method invokes the WRITE-ROW method. The length of the PIXEL-SAMPLES sequence must be equal to the SAMPLES-PER-PIXEL.
Returns the number of pixels left to write to complete the current row of pixels.
All errors signaled by ZPNG are a subtype of ZPNG-ERROR, which is a subtype of CL:ERROR.
A condition of this type is signaled when a PNG with invalid size is created. Valid PNGs have positive width and height.
invalid-size-width condition => width
invalid-size-height condition => height
These accessors provide the invalid size used for a PNG.
A condition of this type is signaled when a row with an incorrect size is passed to WRITE-ROW.
A condition of this type is signaled from FINISH-PNG when it is called before enough rows have been written via WRITE-ROW.
A condition of this type is signaled from FINISH-PNG when it is called on a PIXEL-STREAMED-PNG before the current row of pixels has been completed.
A condition of this type is signaled from WRITE-ROW if it is called more times than is necessary for the given PNG.
A condition of this type is signaled from WRITE-PIXEL if the number of samples in the pixel is not the expected SAMPLES-PER-PIXEL for the given PNG.
Thanks to Patrick Stein for implementing pixel-at-a-time streamed
Please direct any questions, comments, bug reports, or other feedback to Zach Beane.