Image Delivery API

You can use Image Delivery APIs by just appending queries to the image URL:  {image_url}?query_parameter

For example, to resize the width of an image to 100px, you need to append
?width={100} to the image URL. So, the API request would be:

https://images.contentstack.io/v3/assets/blteae40eb499811073/bltc5064f36b5855343/59e0c41ac0eddd140d5a8e3e/owl.jpg?width=100.

You can also use multiple queries in a single API request.

{image_url}?width={width_value}&height={height_value}&resize-filter={resize-filter_value}

In this case, the API request would form like this:

https://images.contentstack.io/v3/assets/blteae40eb499811073/bltc5064f36b5855343/59e0c41ac0eddd140d5a8e3e/owl.jpg?width=500&height=550&resize-filter=nearest

Here’s an example of an asset URL:

https://images.contentstack.io/v3/assets/blteae40eb499811073/bltc5064f36b5855343/59e0c41ac0eddd140d5a8e3e/owl.jpg

If you notice the URL, you will see that it is made up of several strings. Here's the breakdown of these strings to understand what they are:

{base_url}/v3/assets/{stack_api_key}/{asset_uid}/{version_uid}/filename

Please note that the above breakdown of strings of the asset URL is just for your understanding. This is the default pattern of all the asset URLs.

If the "Branches" feature is part of your plan, you will see an updated download URL format for all assets part of any branch, except the default main branch. The branch={branch_UID} query parameter is attached to the download URL.

For instance, if you upload an asset to the development branch, Contentstack generates the following asset download URL:

https://assets.contentstack.com/v3/assets/blt252b550c5ccdae26/bltc56f275260214c0b/61280d9625aca65092ce7f15/Sample_Image.jpg?branch=development

For any asset that you upload to the main branch, Contentstack will continue to generate asset download URLs in the earlier format:

https://assets.contentstack.com/v3/assets/blt252b550c5ccdae26/bltc56f275260214c0b/61280d9625aca65092ce7f15/Sample_Image.jpg

When working with this API documentation, you do not have to enter any of the above values. To make Image Delivery API requests, you simply need to append queries to the asset URL.

Auto

The auto parameter lets you enable the functionality that automates certain image optimization features. As of now, there is only one possible value for this field, i.e., webp. When the auto parameter is set to webp, it enables WebP image support. WebP images have higher compression rate with minimum loss of quality.

Additional Resources: For more information on browsers and operating systems that support WebP images, refer the official WebP doc by Google. You will find additional information on their WebP FAQs page.

Quality

The quality parameter lets you control the compression level of images that have Lossy file format. The value for this parameters can be entered in any whole number (taken as a percentage) between 1 and 100. The lower the number, the smaller will be file size and lower quality, and vice versa. If the source image file is not of Lossy file format, this parameter will be ignored.

Format

The format parameter lets you converts a given image from one format to another. The formats that the source image can be converted to are gif, png, jpg (for JPEG), pjpg (for Progressive JPEG), webp, webpll (Lossless), and webply (Lossy).

Of the formats mentioned above, JPEG, Progressive JPEG, and WEBP (Lossy) support the quality parameter.

Let’s try converting an image to GIF format.

Width

The width parameter lets you dynamically resize the width of the output image by specifying pixels or percentage values. To specify pixel width, use any positive integer between 1 and 8192. For percentage width, use any value between 0.0 and 0.99. To get image width of more than 99 percent, use a value above 99 and append a p parameter to the value. For example, for image width of 300 percent, use width=300p.

The width parameter will automatically adjust the height of the image using the aspect ratio of the image. If the height parameter is specified, the given value will be used. And if both the height and the width parameters are not specified, the dimensions of the input image will be used.

In case the dimensions specified for the output image is greater than the dimensions of the input image, the image will be upscaled. You can disable upscaling of the image by using the disable=upscale parameter. 

Height

The height parameter lets you dynamically resize the height of the output image by specifying pixels or percentage values. To specify pixel height, use any positive integer between 1 and 8192. For percentage height, use any value between 0.0 and 0.99. To get image height of more than 99 percent, use a value above 99 and append a p parameter to the value. For example, for image height of 300 percent, use height=300p.

The height parameter will automatically adjust the width of the image using the aspect ratio of the image. If the width parameter is specified, the given value will be used. And if both the height and the width parameters are not specified, the dimensions of the input image will be used.

In case the dimensions specified for the output image is greater than the dimensions of the input image, the image will be upscaled. You can disable upscaling of the image by using the disable=upscale parameter.

Disable

The disable parameter disables the functionality that is enabled by default. For instance, upscale is always enabled, in which the image is upscaled if the output image (by specifying the width or height) is bigger than the source image. To disable this feature, you can use the query ?disable=upscale. This ensures that even if the specified height or width is much bigger than the actual image, it will not be rendered disproportionately. 

As of now, there is only one value, i.e., upscale, that you can use with the disable parameter.

Crop

The crop parameter allows you to remove pixels from an image. You can crop an image by specifying the height and width in pixels or percentage value, or defining height and width in aspect ratio. You can also define a sub region (i.e., define the starting point for crop) before cropping the image, or you can offset the image on its X and Y axis (i.e., define the centre point of the crop) before cropping the image.

When simply cropping an image, use the query ?crop={width_value},{height_value} to crop the image from the center. The value can be in pixels (for example, ?crop=300,400) or in percentage (for example, ?crop=0.50,0.60) or a combination of both (for example, ?crop=300,0.60). Note that for the percentage value, you can also use the p parameter. For example, 100p for 100%.

Fit to bounds

If fit is set to bounds, it will constrain the given image into the specified height and width.

Fit by cropping

If fit is set to crop, it will crop the given image to the defined height and width.

Trim

The trim parameter lets you trim an image from the edges. This is especially useful for removing border or white spaces that the downloaded images usually come with. The value for this parameter can be given in pixels or percentage. 

You can specify values for top, right, bottom, and left edges of an image. For example, to trim the top edge by 25px, right edge by 50px, bottom edge by 75px and left edge by 100, using the query ?trim=25,50,75,100.

You can also combine two or more values. For example, to trim the top edge by 25px, right edge by 50px, bottom edge by 75px and left edge by 50px, use the query ?trim=25,50,75. Similarly, to trim the top and bottom edge by 50px, and right and left by 100, use ?trim=50,100. To trim all edges by 50px, use ?trim=50.

Orientation

The orient parameter lets you control the cardinal orientation of the given image. Using this parameter, you can orient the image right or left, flip horizontally or vertically or both, and do a lot more. It can automatically correct the orientation of the image if the source image contains orientation details within its EXIF data (Exchangeable Image File Format).

You can use any of the following values for the orient parameter: 

• 1 - Set image to default
• 2 - Flip image horizontally
• 3 - Flip image horizontally and vertically 
• 4 - Flip image vertically
• 5 - Flip image horizontally and then rotate 90 degrees towards left
• 6 - Rotate image 90 degrees towards right
• 7 - Flip image horizontally and then rotate 90 degrees towards right
• 8 - Rotate image 90 degrees towards left

Let’s try to change the orientation of the image. Use the request given below to orient the image right.

Overlay

The overlay parameter allows you to put one image on top of another. You need to specify the relative URL of the image as value for this parameter.

Overlay Align

The overlay-align parameter lets you define the position of the overlay image. The acceptable values for this parameter are given below:

• top: Align the overlay image to the top of the actual image 
• bottom: Align the overlay image to the bottom of the actual image  
• left: Align the overlay image to the left of the actual image 
• right: Align the overlay image to the right of the actual image 
• middle: Align the overlay image to the middle (vertically) of the actual image  
• center: Align the overlay image to the center (horizontally) of the actual image 

You can also specify two values for this parameter, for example ?overlay-align=left,bottom. By default, the overlay alignment is set to middle,center.

Overlay Repeat

The overlay-repeat parameter lets you define how the overlay image will be repeated on the given image. The three acceptable values for this parameter are given below:

• x: Horizontal repetition
• y: Vertical repetition
• both: Horizontal and vertical repetition

Let’s use these different parameters to understand how they work. First, try the horizontal repetition of overlay image.

Overlay Width

The overlay-width parameter lets you define the width of the overlay image. The value for this parameter can be set in pixels or percentage. For pixel value, use any whole number between 1 and 8192. For percentage value, use any decimal number between 0.0 and 0.99. When height is defined in percentage, it relative to the output image.

In order to set the overlay image width to more than 99%, use the p parameter along with the value, for example, ?overlay-width=300p. If the overlay image width exceeds the width of the image, the overlay image will be cropped.

Overlay Height

The overlay-height parameter lets you define the height of the overlay image. The value for this parameter can be set in pixels or percentage. For pixel value, use any whole number between 1 and 8192. For percentage value, use any decimal number between 0.0 and 0.99. When height is defined in percentage, it relative to the output image.

In order to set the overlay image height to more than 99%, use the p parameter along with the value, for example, ?overlay-height=300p. If the overlay image height exceeds the height of the image, the overlay image will be cropped.

Blur

The blur parameter allows you to decrease the focus and clarity of a given image. To specify the extent to which you need to increase the blurriness of an image, use any decimal number (float) between 1 and 1000.

To increase the blurriness of an image by 40, use the following query:

Frame

The frame parameter fetches the first frame from an animated GIF (Graphics Interchange Format) file that comprises a sequence of moving images.

To extract the first frame from the following animated GIF: {GIF_name}, try the following query:

Sharpen

The sharpen parameter allows you to increase the definition of the edges of objects in an image. This helps render a clear image with high detail and sharpness. You need to specify the following values for this parameter:

• a{value}: Amount (a) specifies the amount of contrast to be set for the image edges that you need to sharpen. This amount value is defined as the difference between the darkest and lightest tones in a given image.
• r{value}: Radius (r) specifies the radius of the image edges that you need to sharpen. A lower radius value sharpens only the pixels around the edges, while a higher radius value helps the sharpening effect spread over a broader band of pixels.
  
  

  Tip: The radius value is directly proportional to the size of an image. For example, to get a balanced sharpening effect for two images with 3000x3000 pixels and 1000x1000 pixels, you need to set a radius value of 3 pixels for the larger image and 1 pixel for the smaller image.

• t{value}: Threshold (t) specifies the range of image edges that need to be ignored while sharpening an image. The threshold value sharpens the more noticeable edges of an image and leaves the edges with minor details untouched. For example, to sharpen an image of a human face, you would want to sharpen only the facial characteristics such as eyes, nose, or lips, and not concentrate on minor details such as pimples and birthmarks.

Let us try to increase the sharpness of a given image by amount:2, radius:1000, and threshold:2.

Saturation

The saturation parameter allows you to increase or decrease the intensity of the colors in a given image. To specify the saturation for an image, use a whole number (integer) between -100 and 100. You can also define saturation using any decimal number between -100.00 and 100.00.

To increase the value of the saturation parameter of an image, pass a positive value:

Contrast

The contrast parameter allows you to increase or decrease the difference between the darkest and lightest tones in a given image. To specify contrast for an image, use a whole number (integer) between -100 and 100. You can also define contrast using any decimal number between -100.00 and 100.00.

To increase the value of the contrast parameter of an image, pass a positive value:

Brightness

The brightness parameter allows you to increase or decrease the intensity with which an image reflects or radiates perceived light. To specify brightness for an image, use a whole number (integer) between -100 and 100. You can also define brightness using any decimal number between -100.00 and 100.00.

To increase the value of the brightness parameter of an image, pass a positive value:

Resize-filter

The resize-filter parameter allows you to use the resizing filter to increase or decrease the number of pixels in a given image. This parameter resizes the given image without adding or removing any data from it.

The following values are acceptable for the resize-filter parameter:

• nearest: Utilizes the values of the neighboring translated pixels to provide smoother and quick resizing of a given image.
• bilinear: Utilizes a 2x2 environment of pixels on an average. This filter blends new interpolated pixels with the original image pixels to generate a larger image with more detail.
• bicubic: Utilizes a 4x4 environment of pixels on average. This filter maintains the innermost pixels and discards all the extra details from a given image.
• lanczos2: Enhances the ability to identify linear features and object edges of a given image. This filter uses the sinc resampling function to reconstruct the pixelation of an image and improve its quality.
• lanczos3: Utilizes a better approximation of the sinc resampling function to generate an image with better reconstruction.

You can use the ?resize-filter={resize_filter_value} query to resize an image through the resizing filter. Let us look at some examples to understand how we can use the resize-filter parameter.

Warning: If you only specify the resize-filter parameter, the API request will simply return the original image. You need to also specify either the width or height parameter in the API request to ensure that the resize-filter parameter is not ignored.

Use the ?resize-filter=nearest query to generate an image using the nearest resizing filter.

Canvas

The canvas parameter allows you to increase the size of the canvas that surrounds an image. You can specify the height and width of the canvas area in pixels or percentage or define the height and width of the aspect ratio of the canvas. You can also define the starting point for the canvas area or offset the canvas on its X and Y axis.

You can use the query ?canvas={width_value},{height_value} to set the height and width of the canvas area of the image from the center. The values can be in pixels (for example, ?canvas=700,800) or in percentage (for example, ?canvas=0.70,0.80) or a combination of both (for example, ?canvas=700,0.80).

Tip: You can also define the width and height of the canvas area in aspect ratio (for example, ?canvas=2:3).