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:
download_url?imageMogr2/contrast/<value>
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>"
}]
}
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.)
Operation: contrast
Parameter | Description |
---|---|
download_url | URL of the input image, formatted as &dxlt;BucketName-APPID>.cos.&dxlt;Region>.myqcloud.com/&dxlt;picture name> Example: examplebucket-1250000000.cos.ap-shanghai.myqcloud.com/picture.jpeg |
/contrast/ |
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. |
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:
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.
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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