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1 # The digilib Scaler API
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2
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3 The Scaler servlet takes parameters in the HTTP request format:
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4
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5 Scaler/request_path/?param1=value1¶m2=value2&...
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6
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7 Unknown parameters will be silently ignored.
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8
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9 Recognised parameters (as of Version 2.2.2, for the most recent list of
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10 parameters
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11 [use the source](http://hg.berlios.de/repos/digilib/file/default/servlet/src/main/java/digilib/conf/DigilibServletRequest.java)
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12 ):
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13
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14 - `request_path`: path to file or directory.
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15 - `fn`: path to file or directory. This path will be added to the
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16 `request_path` behind the servlet name. Either parameter can be
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17 empty. All paths are relative to the configured base directory
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18 (digilib-config parameter `basedir-list`).
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19 - `pn`: page number. Index into the (alphabetically sorted)
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20 directory given by the path. Starts with 1. Ignored if the path
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21 points to a file. Default: 1.
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22 - `dw`: destination image width (pixels). If omitted the image is
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23 scaled to fit `dh.`
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24 - `dh`: destination image height (pixels). If omitted the image
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25 is scaled to fit `dw`.
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26 - `wx`: relative x offset of the image area to be sent (0 <=
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27 `wx` <= 1). Default: 0.
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28 - `wy`: relative y offset of the image area to be sent (0 <=
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29 `wy` <= 1). Default: 0.
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30 - `ww`: relative width of the image area to be sent (0 <= `ww`
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31 <= 1). Default: 1.
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32 - `wh`: relative height of the image area to be sent (0 <= `wh`
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33 <= 1). Default: 1.
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34 - `ws`: additional scaling factor. The resulting image will have
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35 the size \[`ws`\*`dw` x `ws`\*`dh`\]. Default: 1.
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36 - `cont`: change contrast of the image. Negative values reduce
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37 contrast, positive values enhance contrast. Pixel value is
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38 multiplied by 2^`cont`. Default: 0
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39 - `brgt`: change brightness of image. Negative value reduces
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40 brightness, positive value enhances brightness. The value `brgt` is
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41 added to the pixel value. Default: 0
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42 - `rot`: rotate image. Rotation angle is given in degrees.
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43 Default: 0
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44 - `rgbm`: modify colour by multiplication. The contrast of the
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45 red green and blue components of the image can be reduced or
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46 enhanced similar to the `cont` parameter. The factors for red, green
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47 and blue are separated by slashes (e.g. `0.86/0/-0.5`).
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48 Default: `0/0/0`
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49 - `rgba`: modify colour by addition. The brightness of the red
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50 green and blue components of the image can be reduced or enhanced
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51 similar to the `brgt` parameter. The factors for red, green and blue
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52 are separated by slashes (e.g. `100/0/25`). Default: `0/0/0`
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53 - `ddpi`: resolution of client display for `osize` mode. Either
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54 `ddpi` or `ddpix` and `ddpiy` must be set to use `osize` mode.
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55 - `ddpix`: resolution of client display in x direction for
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56 `osize` mode.
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57 - `ddpiy`: resolution of client display in y direction for
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58 `osize` mode.
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59 - `scale`: absolute scale factor applied to the highest resolution image
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60 for `ascale` mode.
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61 - `colop`: additional color operation. One of "GRAYSCALE" (produces grayscale
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62 image), "NTSC\_GRAY" (uses NTSC formula to produce grayscale image),
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63 "INVERT" (inverts colors), "MAP\_GRAY\_BGR" (produces false-color image).
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64 - `mo`: list flags for the mode of operation separated by comma ",".
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65 - `fit`: always scale the image to fit \[`dw` x `dh`\] (default).
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66 - `clip`: send the file in its original resolution, cropped
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67 to fit \[`dw` x `dh`\].
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68 - `osize`: scale to original size based on image
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69 resolution (from the image metadata) and display resolution
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70 (from parameter ddpi). Fails if either resolution is unknown.
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71 - `ascale`: scale the highest resolution image by an absolute
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72 factor given by the `scale` parameter.
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73 - `file`: send the file as-is (may be very large and all
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74 sorts of image types!). If configuration doesn't allow sending
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75 files (`sendfile-allowed=false`) revert to `clip`.
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76 - `rawfile`: send the file as-is with a mime-type of
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77 "application/octet-stream" so it can be downloaded with the
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78 browser.
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79 - `errtxt`: send error response as plain text.
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80 - `errimg`: send error response as image (default).
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81 - `errcode`: send error response as HTTP status code.
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82 - `q0`-`q2`: quality of interpolation in scaling (q0:
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83 worst, default).
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84 - `lores`: try to use scaled image (default)
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85 - `hires`: always use the highest resolution image.
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86 - If the image is zoomed (`ww`, `wh` \< 1) the use of the scaled
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87 image files depends on the requested resolution.
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88 - `vmir`: mirror image vertically.
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89 - `hmir`: mirror image horizontally.
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90 - `jpg`: the resulting image is always sent as JPEG
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91 (otherwise TIFF and PNG images are sent as PNG).
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92 - `png`: the resulting image is always sent as PNG
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93 (otherwise JPEG and J2K images are sent as JPEG).
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94
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95 The image to be loaded can be specified by the `request_path`
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96 (deprecated) or the `fn` parameter (preferred) and the optional
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97 index `pn`:
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98
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99 - if `fn` points to a directory then the file with the index `pn`
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100 (in alphabetical order according to ASCII) will be loaded
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101 - if `fn` points to a file (with or without extension) then this
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102 file will be loaded
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103
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104 Find more information on the directory layout [here](image-directories.html).
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105
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106 The image will always be scaled equally in horizontal and vertical direction,
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107 preserving the aspect ratio,
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108 such that the resulting image does not exceed the rectangle \[`dw` x `dh`\].
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109
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110 If only either height or width is given the image is scaled to match
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111 only the given dimension. The size of the resulting image in the other
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112 dimension is determined by the aspect ratio of the image.
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