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date Fri, 06 Sep 2013 11:06:00 +0200
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1 # The digilib Scaler API
2
3 The Scaler servlet takes parameters in the HTTP request format:
4
5 Scaler/request_path/?param1=value1&param2=value2&...
6
7 Unknown parameters will be silently ignored.
8
9 Recognised parameters (as of Version 2.2.2, for the most recent list of
10 parameters
11 [use the source](http://hg.berlios.de/repos/digilib/file/default/servlet/src/main/java/digilib/conf/DigilibServletRequest.java)
12 ):
13
14 - `request_path`: path to file or directory.
15 - `fn`: path to file or directory. This path will be added to the
16 `request_path` behind the servlet name. Either parameter can be
17 empty. All paths are relative to the configured base directory
18 (digilib-config parameter `basedir-list`).
19 - `pn`: page number. Index into the (alphabetically sorted)
20 directory given by the path. Starts with 1. Ignored if the path
21 points to a file. Default: 1.
22 - `dw`: destination image width (pixels). If omitted the image is
23 scaled to fit `dh.`
24 - `dh`: destination image height (pixels). If omitted the image
25 is scaled to fit `dw`.
26 - `wx`: relative x offset of the image area to be sent (0 <=
27 `wx` <= 1). Default: 0.
28 - `wy`: relative y offset of the image area to be sent (0 <=
29 `wy` <= 1). Default: 0.
30 - `ww`: relative width of the image area to be sent (0 <= `ww`
31 <= 1). Default: 1.
32 - `wh`: relative height of the image area to be sent (0 <= `wh`
33 <= 1). Default: 1.
34 - `ws`: additional scaling factor. The resulting image will have
35 the size \[`ws`\*`dw` x `ws`\*`dh`\]. Default: 1.
36 - `cont`: change contrast of the image. Negative values reduce
37 contrast, positive values enhance contrast. Pixel value is
38 multiplied by 2^`cont`. Default: 0
39 - `brgt`: change brightness of image. Negative value reduces
40 brightness, positive value enhances brightness. The value `brgt` is
41 added to the pixel value. Default: 0
42 - `rot`: rotate image. Rotation angle is given in degrees.
43 Default: 0
44 - `rgbm`: modify colour by multiplication. The contrast of the
45 red green and blue components of the image can be reduced or
46 enhanced similar to the `cont` parameter. The factors for red, green
47 and blue are separated by slashes (e.g. `0.86/0/-0.5`).
48 Default: `0/0/0`
49 - `rgba`: modify colour by addition. The brightness of the red
50 green and blue components of the image can be reduced or enhanced
51 similar to the `brgt` parameter. The factors for red, green and blue
52 are separated by slashes (e.g. `100/0/25`). Default: `0/0/0`
53 - `ddpi`: resolution of client display for `osize` mode. Either
54 `ddpi` or `ddpix` and `ddpiy` must be set to use `osize` mode.
55 - `ddpix`: resolution of client display in x direction for
56 `osize` mode.
57 - `ddpiy`: resolution of client display in y direction for
58 `osize` mode.
59 - `scale`: absolute scale factor applied to the highest resolution image
60 for `ascale` mode.
61 - `colop`: additional color operation. One of "GRAYSCALE" (produces grayscale
62 image), "NTSC\_GRAY" (uses NTSC formula to produce grayscale image),
63 "INVERT" (inverts colors), "MAP\_GRAY\_BGR" (produces false-color image).
64 - `mo`: list flags for the mode of operation separated by comma ",".
65 - `fit`: always scale the image to fit \[`dw` x `dh`\] (default).
66 - `clip`: send the file in its original resolution, cropped
67 to fit \[`dw` x `dh`\].
68 - `osize`: scale to original size based on image
69 resolution (from the image metadata) and display resolution
70 (from parameter ddpi). Fails if either resolution is unknown.
71 - `ascale`: scale the highest resolution image by an absolute
72 factor given by the `scale` parameter.
73 - `file`: send the file as-is (may be very large and all
74 sorts of image types!). If configuration doesn't allow sending
75 files (`sendfile-allowed=false`) revert to `clip`.
76 - `rawfile`: send the file as-is with a mime-type of
77 "application/octet-stream" so it can be downloaded with the
78 browser.
79 - `errtxt`: send error response as plain text.
80 - `errimg`: send error response as image (default).
81 - `errcode`: send error response as HTTP status code.
82 - `q0`-`q2`: quality of interpolation in scaling (q0:
83 worst, default).
84 - `lores`: try to use scaled image (default)
85 - `hires`: always use the highest resolution image.
86 - If the image is zoomed (`ww`, `wh` \< 1) the use of the scaled
87 image files depends on the requested resolution.
88 - `vmir`: mirror image vertically.
89 - `hmir`: mirror image horizontally.
90 - `jpg`: the resulting image is always sent as JPEG
91 (otherwise TIFF and PNG images are sent as PNG).
92 - `png`: the resulting image is always sent as PNG
93 (otherwise JPEG and J2K images are sent as JPEG).
94
95 The image to be loaded can be specified by the `request_path`
96 (deprecated) or the `fn` parameter (preferred) and the optional
97 index `pn`:
98
99 - if `fn` points to a directory then the file with the index `pn`
100 (in alphabetical order according to ASCII) will be loaded
101 - if `fn` points to a file (with or without extension) then this
102 file will be loaded
103
104 Find more information on the directory layout [here](image-directories.html).
105
106 The image will always be scaled equally in horizontal and vertical direction,
107 preserving the aspect ratio,
108 such that the resulting image does not exceed the rectangle \[`dw` x `dh`\].
109
110 If only either height or width is given the image is scaled to match
111 only the given dimension. The size of the resulting image in the other
112 dimension is determined by the aspect ratio of the image.