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    Adjusting Contrast

    Terakhir diperbarui:2024-06-12 15:20:05
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      Overview

      COS uses the imageMogr2 API provided by CI to adjust an image’s contrast, which is the difference in luminance between the brightest and darkest points in an image (i.e., the contrast in grayscale).
      An image can be processed:
      Upon download
      Upon upload
      In cloud

      Restrictions

      Format: Currently, JPG, BMP, GIF, PNG, and WebP images can be processed, and HEIF images can be decoded and processed.
      Size: The 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, the total number of pixels (Width x Height x Number of frames) cannot exceed 250 million pixels.
      Number of frames (for animated images): For GIF, the number of frames cannot exceed 300.

      API Format

      1. Processing upon download

      download_url?imageMogr2/contrast/<value>

      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": "imageMogr2/contrast/<value>"
        }]
      }

      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": "imageMogr2/contrast/<value>"
        }]
      }
      Note:
      Authorization: Auth String (For more information, please see Request Signature.)

      Parameters

      Operation: contrast
      Parameter
      Description
      download_url
      URL of the input image, formatted as &lt;BucketName-APPID>.cos.&lt;Region>.myqcloud.com/&lt;picture name>
      Example: examplebucket-1250000000.cos.ap-shanghai.myqcloud.com/picture.jpeg
      /contrast/<value>
      Adjusts the contrast of an image. The value must be an integer in the range of [−100, 100].
      value < 0: reduces the contrast.
      value = 0: does not adjust the contrast.
      value > 0: increases the contrast.
      /ignore-error/1
      If this parameter is carried and the image failed to be processed because it is too large, the input image will be returned with no error reported.

      Examples

      Example 1: adjusting contrast

      Note:
      Processing upon download is used as an example here, which does not store the output image in a bucket. If you need to store the output image, please see Persistent Image Processing and use Processing upon upload or Processing in-cloud data.
      This example reduces the contrast of an image by 50:
      http://examples-1251000004.cos.ap-shanghai.myqcloud.com/sample.jpeg?imageMogr2/contrast/-50
      Output image:
      
      

      Example 2: adjusting contrast with a signature carried

      This example processes the image in the same way as in the example 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>&imageMogr2/contrast/-50
      Note:
      You can obtain the value of <signature> by referring to 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 example for your reference (it might have expired or become inaccessible). For more information, please see Request Signature.
      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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