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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 query string format:
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4
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5 http://host.domain/digilib/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 2.5.0, for the most up to date information use the source for
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10 [parameters](https://sourceforge.net/p/digilib/code/ci/default/tree/servlet/src/main/java/digilib/conf/DigilibServletRequest.java)
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11 and
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12 [mode options](https://sourceforge.net/p/digilib/code/ci/default/tree/common/src/main/java/digilib/conf/DigilibOption.java)
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13 ):
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14
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15 - `request_path`: (optional) path to file or directory.
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16 - `fn`: path to file or directory. (This path will be added to
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17 `request_path`. Either parameter can be empty.
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18 All paths are relative to the configured base directory
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19 from the [digilib-config.xml](digilib-config.html) parameter `basedir-list`).
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20 - `pn`: page number. Index into the (alphabetically sorted)
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21 directory given by the path. Starts with 1. Ignored if the path
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22 points to a file. Default: 1.
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23 - `dw`: destination image width (pixels). If omitted the image is
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24 scaled to fit `dh.`
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25 - `dh`: destination image height (pixels). If omitted the image
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26 is scaled to fit `dw`.
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27 - `wx`: relative x offset of the image area to be sent (0 <=
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28 `wx` <= 1). Default: 0.
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29 - `wy`: relative y offset of the image area to be sent (0 <=
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30 `wy` <= 1). Default: 0.
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31 - `ww`: relative width of the image area to be sent (0 <= `ww`
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32 <= 1). Default: 1.
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33 - `wh`: relative height of the image area to be sent (0 <= `wh`
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34 <= 1). Default: 1.
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35 - `ws`: additional scaling factor. The resulting image will have
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36 the size \[`ws`\*`dw` x `ws`\*`dh`\]. Default: 1.
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37 - `cont`: change contrast of the image. Negative values reduce
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38 contrast, positive values enhance contrast. Each pixel value is
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39 multiplied by 2^`cont`. Default: 0
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40 - `brgt`: change brightness of image. Negative value reduces
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41 brightness, positive value enhances brightness. The value `brgt` is
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42 added to each pixel value. Default: 0
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43 - `rot`: rotate image. Rotation angle is given in degrees.
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44 Default: 0
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45 - `rgbm`: modify colour by multiplication. The contrast of the
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46 red green and blue components of the image can be reduced or
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47 enhanced similar to the `cont` parameter. The factors for red, green
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48 and blue are separated by slashes (e.g. `0.86/0/-0.5`).
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49 Default: `0/0/0`
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50 - `rgba`: modify colour by addition. The brightness of the red
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51 green and blue components of the image can be reduced or enhanced
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52 similar to the `brgt` parameter. The factors for red, green and blue
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53 are separated by slashes (e.g. `100/0/25`). Default: `0/0/0`
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54 - `ddpi`: resolution of client display for `osize` mode. Either
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55 `ddpi` or `ddpix` and `ddpiy` must be set to use `osize` mode.
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56 - `ddpix`: resolution of client display in x direction for
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57 `osize` mode.
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58 - `ddpiy`: resolution of client display in y direction for
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59 `osize` mode.
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60 - `scale`: absolute scale factor applied to the highest resolution image
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61 for `ascale` mode.
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62 - `colop`: color operation. One of
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63 - `GRAYSCALE` (produces grayscale image)
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64 - `NTSC_GRAY` (uses NTSC formula to produce grayscale image)
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65 - `BITONAL` (produces black-and-white image)
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66 - `INVERT` (inverts colors)
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67 - `MAP_GRAY_BGR` (produces false-color image mapping brightness values to color scale from blue via green to red).
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68 - `mo`: list of options for the mode of operation separated by comma ",".
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69 - `fit`: scale the (selected area of the) image proportionally to fit inside [dw x dh], preserving its aspect ratio (default).
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70 - `squeeze`: scale the (selected area of the) image to fill [dw x dh], changing its aspect ratio (since v2.3.3).
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71 - `crop`: scale the (selected area of the) image proportionally to fill [dw x dh] with the shorter side, cropping the longer side (since v2.5).
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72 - `fill`: scale the (selected area of the) image proportionally to fill [dw x dh] with the longer side, filling out the image on the shorter side if possible (since v2.3.3).
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73 - `clip`: send the file in the highest resolution, cropped
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74 to fit \[`dw` x `dh`\].
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75 - `osize`: scale to original size based on image
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76 resolution (from the image metadata) and display resolution
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77 (from parameter ddpi). Fails if either resolution is unknown.
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78 - `ascale`: scale the highest resolution image by an absolute
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79 factor given by the `scale` parameter.
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80 - `file`: send the file as-is (may be very large and all
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81 sorts of image types!). If the configuration doesn't allow sending
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82 files (`sendfile-allowed=false`) revert to `clip`.
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83 - `rawfile`: send the file as-is with a mime-type of
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84 "application/octet-stream" so the browser presents a download dialog.
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85 - `errtxt`: send error response as plain text.
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86 - `errimg`: send error response as image (default).
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87 - `errcode`: send error response as HTTP status code.
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88 - `q0`-`q2`: quality of interpolation in scaling (q0:
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89 worst, q2 best).
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90 - `hires`: only use the highest resolution image.
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91 - `autores`: use the pre-scaled image that is bigger than the requested size (default).
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92 - `lores`: prefer the next-smaller pre-scaled image.
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93 - `vmir`: mirror image vertically.
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94 - `hmir`: mirror image horizontally.
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95 - `jpg`: the resulting image is always sent as JPEG
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96 (otherwise TIFF and PNG images are sent as PNG).
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97 - `png`: the resulting image is always sent as PNG
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98 (otherwise JPEG and J2K images are sent as JPEG).
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99 - `pxarea`: interpret `wx`, `wy`, `ww`, `wh` as pixel coordinates on the highest resolution image.
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100
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101 The image to be loaded is specified by the `request_path`
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102 (deprecated) and/or the `fn` parameter (preferred) and the optional
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103 index `pn`:
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104
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105 - if `fn` points to a directory then the file with the index `pn`
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106 (in alphabetical order according to ASCII) will be loaded
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107 - if `fn` points to a file (with or without extension) then this
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108 file will be loaded (regardless of `pn`).
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109
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110 Find more information on the directory layout [here](image-directories.html).
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111
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112 The image will always be scaled equally in horizontal and vertical direction,
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113 preserving the aspect ratio (except with `mo=squeeze`),
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114 such that the resulting image does not exceed the rectangle \[`dw` x `dh`\].
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115
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116 If only either height or width is given the image is scaled to match
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117 only the given dimension. The size of the resulting image in the other
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118 dimension is determined by the aspect ratio of the image or the selected area.
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