List of all the App Engine images service get_serving_url() URI options

Question

In response to another question, a commenter mentioned an undocumented URI option I was not aware of to flip images horizontally/vertically with the App Engine images service.

The documentation mentions a few basic options:

• =s0 — fullsize
• =s640 — longest edge 640px long
• =s640-c — 640px square

Would be nice to generate a comprehensive list of options, or if someone could provide any more options they know about here to serve as de facto documentation.

Answer 1

Between reading some random posts and manually doing some investigative research, I have put together the following list. Please drop any other knowledge in other answers or in comments and I can integrate it here.

Usage Example

We can effect various image transformations by tacking strings onto the end of an App Engine blob-based image URL, following an = character. Options can be combined by separating them with hyphens, eg.:

http://[image-url]=s200-fh-p-b10-c0xFFFF0000 

or:

http://[image-url]=s200-r90-cc-c0xFF00FF00-fSoften=1,20,0: 

... which have the following effect (documentation below):

As an example of how awesome this is, here's an animated GIF, downsized and inverted:

… which we can then convert into an MP4 video with one extra parameter: click to see MP4 version

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SIZE / CROP

• s640 — generates image 640 pixels on largest dimension
• s0 — original size image
• w100 — generates image 100 pixels wide
• h100 — generates image 100 pixels tall
• s (without a value) — stretches image to fit dimensions
• c — crops image to provided dimensions
• n — same as c, but crops from the center
• p — smart square crop, attempts cropping to faces
• pp — alternate smart square crop, does not cut off faces (?)
• cc — generates a circularly cropped image
• ci — square crop to smallest of: width, height, or specified =s parameter
• nu — no-upscaling. Disables resizing an image to larger than its original resolution.

PAN AND ZOOM

• x, y, z: — pan and zoom a tiled image. These have no effect on an untiled image or without an authorization parameter of some form (see googleartproject.com).

ROTATION

• fv — flip vertically
• fh — flip horizontally
• r{90, 180, 270} — rotates image 90, 180, or 270 degrees clockwise

IMAGE FORMAT

• rj — forces the resulting image to be JPG
• rp — forces the resulting image to be PNG
• rw — forces the resulting image to be WebP

• rg — forces the resulting image to be GIF

• v{0,1,2,3} — sets image to a different format option (works with JPG and WebP)

Forcing PNG, WebP and GIF outputs can work in combination with circular crops for a transparent background. Forcing JPG can be combined with border color to fill in backgrounds in transparent images.

ANIMATED GIFs

• rh — generates an MP4 from the input image
• k — kill animation (generates static image)

MISC.

• b10 — add a 10px border to image
• c0xAARRGGBB — set border color, eg. =c0xffff0000 for red
• d — adds header to cause browser download
• e7 — set cache-control max-age header on response to 7 days
• l100 — sets JPEG quality to 100% (1-100)
• h — responds with an HTML page containing the image
• g — responds with XML used by Google's pan/zoom

Filters

• fSoften=1,100,0: - where 100 can go from 0 to 100 to blur the image
• fVignette=1,100,1.4,0,000000 where 100 controls the size of the gradient and 000000 is RRGGBB of the color of the border shadow
• fInvert=0,1 inverts the image regardless of the value provided
• fbw=0,1 makes the image black and white regardless of the value provided

Unknown Parameters

These parameters have been seen in use, but their effect is unknown: no, nd, mv

Caveats

Some options (like =l for JPEG quality) do not seem to generate new images. If you change another option (size, etc.) and change the l value, the quality change should be visible. Some options also don't work well together. This is all undocumented by Google, probably with good reason.

Moreover, it's probably not a good idea to depend on any of these options existing forever. Google could remove most of them without notice at any time.