Compressed size surprises [was: Lossless webp is smaller than lossy webp]

[Pascal Massimino]

Hi,

On Wed, Nov 23, 2016 at 5:03 PM, Pascal Massimino <pascal.m...@gmail.com> wrote:

Hi Inian,

On Wed, Nov 23, 2016 at 3:54 PM, Inian Parameshwaran <inia...@gmail.com> wrote:

I have hosted a sample image at http://162.243.91.29/icon.png

This is how I am generating my webp images

> cwebp icon.png -o icon.webp

> cwebp -lossless icon.png -o icon-lossless.webp

(original) icon.png = 1760 bytes

(lossy) icon.webp = 704 bytes

(lossless) icon-lossless.webp = 560 bytes

Is this expected behaviour? I had expected lossless size >= lossy size always.

Yes, this is expected (for images with low number of colors, in particular).

You'd get a similar behaviour if you'd try to convert icon.png to a JPEG file instead of PNG.

This has to do with the use of the downsampled YUV420 colorspace, which is well suited for photos, but

less so for low-color sources (=low complexity).

Since this topic (of surprising file size variations) has come up several time,

it probably deserves an entry in the FAQ!

=> https://developers.google.com/speed/webp/faq#can_a_webp_image_grow_larger_than_its_source_image

Hope it clarifies things...

skal/

[Saurabh Khanduja]

Small typo, I think "Yes, usually went converting" should be "Yes, usually when converting"

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Thanks & Regards,

Saurabh Khanduja

Miles of Smiles

[Pascal Massimino]

On Wed, Nov 30, 2016 at 10:13 AM, Saurabh Khanduja <sau...@roposo.com> wrote:

Small typo, I think "Yes, usually went converting" should be "Yes, usually when converting"

Thanks! corrected.