Dimensions and Size of WebP Images

Arun kumar MP

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Aug 17, 2022, 12:42:07 AM8/17/22

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Im getting the size of the webp image from index 8-11
How to get the dimension of webp from image ?

James Zern

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Aug 17, 2022, 1:16:01 AM8/17/22

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Hi,

On Tue, Aug 16, 2022 at 9:42 PM Arun kumar MP <mpar...@gmail.com> wrote:

Im getting the size of the webp image from index 8-11
How to get the dimension of webp from image ?

You can use the WebPGetInfo() or WebPGetFeatures() functions to retrieve this information [1]. In the simple file format [2] the width and height are stored in the lossy and lossless bitstreams. The extended format [3] has a global canvas size, but each frame may have its own dimensions that are <= to the canvas size which are again retrieved from the bitstream.

[1] https://developers.google.com/speed/webp/docs/api#simple_decoding_api

[2] https://developers.google.com/speed/webp/docs/riff_container#simple_file_format_lossy

[3] https://developers.google.com/speed/webp/docs/riff_container#extended_file_format

Arun kumar MP

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Aug 17, 2022, 5:51:41 AM8/17/22

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How can I get the dimensions for webp image in java ?

For verifying the whether the image is webp or not im checking the image byte from from 8-11
is there any way to get the dimension like that ?

James Zern

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Aug 17, 2022, 5:45:42 PM8/17/22

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On Tue, Aug 16, 2022 at 11:17 PM Arun kumar MP <mpar...@gmail.com> wrote:

How can I get the dimensions for webp image in java ?

For verifying the whether the image is webp or not im checking the image byte from from 8-11
is there any way to get the dimension like that ?

You would have to read the values from the bitstream, but as I mentioned there are 3 cases: lossy, lossless and animation. The WebPGetInfo() and WebPGetFeatures() calls get the values with ParseHeadersInternal() [4]. You can take a look at the code to get an idea of how the values are extracted.

Android provides this information in Java with the ImageDecoder.ImageInfo class [5].

[4] https://chromium.googlesource.com/webm/libwebp/+/refs/tags/v1.2.4/src/dec/webp_dec.c#277

[5] https://developer.android.com/reference/android/graphics/ImageDecoder.ImageInfo

James Zern

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Aug 17, 2022, 5:47:36 PM8/17/22

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On Wed, Aug 17, 2022 at 2:45 PM James Zern <jz...@google.com> wrote:

On Tue, Aug 16, 2022 at 11:17 PM Arun kumar MP <mpar...@gmail.com> wrote:
How can I get the dimensions for webp image in java ?

For verifying the whether the image is webp or not im checking the image byte from from 8-11
is there any way to get the dimension like that ?

You would have to read the values from the bitstream, but as I mentioned there are 3 cases: lossy, lossless and animation. The WebPGetInfo() and WebPGetFeatures() calls get the values with ParseHeadersInternal() [4]. You can take a look at the code to get an idea of how the values are extracted.
Android provides this information in Java with the ImageDecoder.ImageInfo class [5].

I forgot to mention that WebPGetInfo() is also available via SWIG bindings in libwebp [6].

[4] https://chromium.googlesource.com/webm/libwebp/+/refs/tags/v1.2.4/src/dec/webp_dec.c#277
[5] https://developer.android.com/reference/android/graphics/ImageDecoder.ImageInfo

[6] https://chromium.googlesource.com/webm/libwebp/+/refs/tags/v1.2.4/swig/

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