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Image Watermarking

Last updated: 2022-05-17 15:58:23

    Overview

    CI's image watermarking feature is implemented through the watermark API. Currently, only image watermarks stored in CI are supported. An input image cannot be larger than 32 MB, with its width and height not exceeding 30,000 pixels and the total number of pixels not exceeding 250 million. The width and height of the output image cannot exceed 9,999 pixels. For an input animated image, its total number of pixels (width x height x number of frames) cannot exceed 250 million.

    An image can be processed:

    • Upon download
    • Upon upload
    • In cloud
    Note:

    • You can overlay up to ten image watermarks over a single image.
    • An animated image cannot be used as a watermark.

    API Sample

    1. Processing upon download

    download_url?watermark/1/image/<encodedURL>
                          /gravity/<gravity>
                          /dx/<dx>
                          /dy/<dy>
                          /blogo/<type>
    
    Note:

    Spaces and line breaks above are for readability only and can be ignored.

    2. Processing upon upload

    PUT /<ObjectKey> HTTP/1.1
    Host: <BucketName-APPID>.cos.<Region>.myqcloud.com
    Date: GMT Date
    Authorization: Auth String
    Pic-Operations: 
    {
    "is_pic_info": 1,
    "rules": [{
        "fileid": "exampleobject",
        "rule": "watermark/1/image/<encodedURL>
                          /gravity/<gravity>
                          /dx/<dx>
                          /dy/<dy>
                          /blogo/<type>"
    }]
    }
    

    3. Processing in-cloud data

    POST /<ObjectKey>?image_process HTTP/1.1
    Host: <BucketName-APPID>.cos.<Region>.myqcloud.com
    Date: GMT Date
    Content-length: Size
    Authorization: Auth String
    Pic-Operations: 
    {
    "is_pic_info": 1,
    "rules": [{
        "fileid": "exampleobject",
        "rule": "watermark/1/image/<encodedURL>
                          /gravity/<gravity>
                          /dx/<dx>
                          /dy/<dy>
                          /blogo/<type>"
    }]
    }
    
    Note:

    Authorization: Auth String (for more information, see Request Signature).

    Parameters

    In the code above, watermark is the operation name and the number 1 indicates that the watermark is an image.

    Parameter Description
    download_url URL of the input image in the format of &lt;BucketName-APPID>.cos.&lt;Region>.myqcloud.com/&lt;picture name>.
    For example, examplebucket-1250000000.cos.ap-shanghai.myqcloud.com/picture.jpeg
    /image/ URL-safe Base64-encoded URL of the image watermark. For example, if the image watermark URL is http://examplebucket-1250000000.cos.ap-shanghai.myqcloud.com/shuiyin_2.png, you should set this parameter to aHR0cDovL2V4YW1wbGVidWNrZXQtMTI1MDAwMDAwMC5jb3MuYXAtc2hhbmdoYWkubXlxY2xvdWQuY29tL3NodWl5aW5fMi5wbmc.
    /gravity/ Position of the text watermark, which is a square in a 3x3 grid. Default value: SouthEast
    /dx/ Horizontal margin in pixels. Default value: 0
    /dy/ Vertical margin in pixels. Default value: 0
    /blogo/ Adaptation mode for an image watermark that is larger than the input image. Valid values:
  • 1: Scales the image watermark to the size of the input image.
  • 2: Crops the image watermark to the size of the input image.
  • /scatype/ Scaling mode for the image watermark (relative to the input image). This parameter must be used together with /spcent/. Valid values:
  • 1: Scales by width.
  • 2: Scales by height.
  • 3: Scales by area.
  • /spcent/ Scale ratio of the image watermark in permillage. This parameter must be used together with /scatype/. Value range:
  • [1,1000] (if /scatype/ is set to 1)
  • [1,1000] (if /scatype/ is set to 2)
  • [1,250] (if /scatype/ is set to 3)
    For example, http://examples-1251000004.cos.ap-shanghai.myqcloud.com/sample.jpeg?watermark/1/image/xxxxxxx/scatype/3/spcent/250
  • /dissolve/ Opacity of the image watermark. Value range: 1−100. Default value: 90 (indicating 90% opacity)
    /batch/ Whether to tile the image watermark. If this parameter is set to 1, the image watermark will be tiled across the input image.
    /degree/ Angle to rotate the image watermark. This parameter is valid only when /batch/ is set to 1. Value range: 0−360. Default value: 0
    Note:

    An image watermark must:

    • Be stored in the same bucket as the input image.
    • Have a URL containing a COS domain name (a CDN acceleration domain name such as examplebucket-1250000000.file.myqcloud.com/shuiyin_2.png is unsupported) and be accessible (if the image watermark is set to private-read, it must carry a signature).
    • Have a URL starting with http://. Note that http:// cannot be omitted or changed to https://. For example, examplebucket-1250000000.cos.ap-shanghai.myqcloud.com/shuiyin_2.png and https://examplebucket-1250000000.cos.ap-shanghai.myqcloud.com/shuiyin_2.png are invalid watermark URLs.

    3x3 Grid Position Diagram

    The 3x3 grid position diagram is as follows. Once you specify the gravity parameter for an operation, the corresponding red dot becomes the reference point, and offsets will be relative to this point.

    Note:

    • If gravity is set to center, dx and dy are invalid.
    • If gravity is set to north or south, dx is invalid.
    • If gravity is set to west or east, dy is invalid.

    Use Cases

    Note:

    Processing upon download is used as a use case here, which does not store the output image in a bucket. If you need to store the output image, see Persistent Image Processing and use Processing upon upload or Processing in-cloud data.

    Use case 1. Adding an image watermark

    http://examples-1251000004.cos.ap-shanghai.myqcloud.com/sample.jpeg?watermark/1/image/aHR0cDovL2V4YW1wbGVzLTEyNTEwMDAwMDQucGljc2gubXlxY2xvdWQuY29tL3NodWl5aW4uanBn/gravity/southeast
    

    After an image watermark is added:

    Use case 2. Adding an image watermark with the tile mode and opacity specified

    https://examples-1251000004.cos.ap-shanghai.myqcloud.com/sample.jpeg?watermark/1/image/aHR0cDovL2V4YW1wbGVzLTEyNTEwMDAwMDQucGljc2gubXlxY2xvdWQuY29tL3NodWl5aW4uanBn/gravity/southeast/batch/1/degree/45/dissolve/40/
    

    The effect of an added image watermark rotated by 45 degrees and tiled with 40% opacity is as follows:

    Use case 3. Adding an image watermark with a signature carried

    This use case processes the image in the same way as in the use case above except that a signature is carried. The signature is joined with other processing parameters using an ampersand (&).

    http://examples-1251000004.cos.ap-shanghai.myqcloud.com/sample.jpeg?q-sign-algorithm=<signature>&watermark/1/image/aHR0cDovL2V4YW1wbGVzLTEyNTEwMDAwMDQucGljc2gubXlxY2xvdWQuY29tL3NodWl5aW4uanBn/gravity/southeast
    
    Note:

    You can obtain the value of &lt;signature> as instructed in Request Signature.

    Notes

    To prevent unauthorized users from accessing or downloading the input image by using a URL that does not contain any processing parameter, you can add the processing parameters to the request signature, making the processing parameters the key of the parameter with the value left empty. The following is a simple sample for your reference (it might have expired or become inaccessible). For more information, see Upload via Pre-Signed URL.

    http://examples-1251000004.cos.ap-shanghai.myqcloud.com/sample.jpeg?q-sign-algorithm=sha1&q-ak=AKID********************&q-sign-time=1593342360;1593342720&q-key-time=1593342360;1593342720&q-header-list=&q-url-param-list=watermark%252f1%252fimage%252fahr0cdovl2v4yw1wbgvzlteyntewmdawmdqucgljc2gubxlxy2xvdwquy29tl3nodwl5aw4uanbn%252fgravity%252fsoutheast&q-signature=26a429871963375c88081ef60247c5746e834a98&watermark/1/image/aHR0cDovL2V4YW1wbGVzLTEyNTEwMDAwMDQucGljc2gubXlxY2xvdWQuY29tL3NodWl5aW4uanBn/gravity/southeast
    
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