Re: Proposed reply to WHATWG comments re: Float16Array + HTML Canvas

RE changing to Uint8ClampedArray instead of Float32Array by default: I view
this as fixing a bug in the proposal. Changing the type that is returned by
a call sets up naive users of the API for A Bad Time in many ways.

On Tue, Feb 14, 2023 at 1:24 AM Lars Borg <borg@adobe.com> wrote:

> In today's call there was a Q:
> Q: Can float16 represent unsigned integers (such as video signals)
> accurately up to bit depth N?
> A: Float16 can represent unsigned integers accurately up to bit depth 11,
> or 2047.
>
> Details:
> In float16 the mantissa field is 10 bits long. The most significant
> mantissa bit is implied, not stored, and set to 1. The largest mantissa is
> thus x7FF = 2047 = 11 bits.
>  A 12bit unsigned integer signal stored as float16 would lose the LSB for
> 1023 values in range x801 to xFFF, while values up to x800 would be stored
> losslessly.
> This holds true whether the integer values are scaled to float with a
> divisor of 1, 2,... 2^N, or 2^N-1.
> If the divisor is 2^N-1, the value must be rounded or truncated when
> converting back to integer.
>
> Lars
>
> -----Original Message-----
> From: Pierre Lemieux <pal@sandflow.com <mailto:pal@sandflow.com>>
> Date: Monday, February 13, 2023 at 1:16 PM
> To: "public-colorweb@w3.org <mailto:public-colorweb@w3.org>" <
> public-colorweb@w3.org <mailto:public-colorweb@w3.org>>
> Cc: Chris Needham <chris.needham@bbc.co.uk <mailto:chris.needham@bbc.co.uk>>,
> Christopher Cameron <ccameron@google.com <mailto:ccameron@google.com>>
> Subject: Proposed reply to WHATWG comments re: Float16Array + HTML Canvas
> Resent-From: <public-colorweb@w3.org <mailto:public-colorweb@w3.org>>
> Resent-Date: Monday, February 13, 2023 at 1:16 PM
>
>
> EXTERNAL: Use caution when clicking on links or opening attachments.
>
>
>
>
> Good morning/evening,
>
>
> Per our earlier call, below is the proposed response to the WHATWG
> feedback, which I plan to post by 2023-02-14 COB unless objections are
> raised.
>
>
> Best,
>
>
> -- Pierre
>
>
> """
> Can you confirm that the concern is with selecting Float32Array as the
> default readback type? If so, we are considering using
> Uint8ClampedArray as the default readback type instead, opening the
> door for Float16Array and other types to be offered down the line.
>
>
> We are also happy to support the Float16Array proposal in TC 39. Let
> us know how to best coordinate the effort/proceed.
>
>
> In the meantime, are there objections to supporting Float32Array as
> one of the (non-default) readback types, while the Float16Array
> proposal makes its way through the TC 39 process?
> """
>
>
>
>
>
>
> On Mon, Feb 13, 2023 at 12:28 PM Christopher Cameron
> <ccameron@google.com <mailto:ccameron@google.com>> wrote:
> >
> > Alternative proposal: Make the default readback format always be
> Uint8ClampedArray.
> >
> > For color space, we had the default readback color space match the
> canvas' color space.
> >
> > The plus side that a naive getImageData-then-putImageData doesn't lose
> data.
> > The minus side is that a naive application may assume all ImageDatas are
> sRGB, and get slightly-incorrect results.
> >
> > For the type, I think there's a strong case for Uint8ClampedArray being
> the universal default.
> >
> > The plus side is that a naive getImageData+putImageData doesn't lose
> data.
> > The minus side is that a naive application will assume all ImageDatas
> are Uint8ClampedArray and just crash (or worse) when given data that
> floating point.
> >
> > The guiding principle is "make naive use of non-default canvases work
> reasonably". To think of it, defaulting to Float16Array is pretty
> dangerous, and breaks this principle.
> >
> > On Wed, Feb 8, 2023 at 10:08 PM Chris Needham <chris.needham@bbc.co.uk
> <mailto:chris.needham@bbc.co.uk>> wrote:
> >>
> >> Hi Pierre,
> >>
> >> > Is there a concrete timeline for Float16Array, which would cause the
> Color CG to revisit its recommendations?
> >>
> >> Can we answer this question rather than ask Anne?
> >
> >
> > In some emails, someone said "maybe a year". So creating a dependency on
> Float16Array puts this project on ice for a year. And that's only if
> multiple browsers decide that float16 is worth staffing immediately (very
> unlikely).
> >
> > Of note is that WebGL and WebGPU can create floating point canvases
> today (well, almost today, for WebGL), and so it will be acceptable to
> leave this feature out of reach to "simpler" applications that use 2D
> canvas.
> >
> >
> >>
> >> Can we progress Float16Array within TC39? It's currently a stage 1
> proposal:
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Ftc39%2Fproposals%2Fblob%2Fmain%2Fstage-1-proposals.md&data=05%7C01%7Cborg%40adobe.com%7C1ad998daefba43f9858a08db0e184a68%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C638119269715896653%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=NPqBbKS3BPkcUSoVfHfUG3qH%2BLLeHozVrSLZeISnF6Y%3D&reserved=0
> <
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Ftc39%2Fproposals%2Fblob%2Fmain%2Fstage-1-proposals.md&amp;data=05%7C01%7Cborg%40adobe.com%7C1ad998daefba43f9858a08db0e184a68%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C638119269715896653%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=NPqBbKS3BPkcUSoVfHfUG3qH%2BLLeHozVrSLZeISnF6Y%3D&amp;reserved=0
> >
> >>
> >> See
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftc39.es%2Fprocess-document%2F&data=05%7C01%7Cborg%40adobe.com%7C1ad998daefba43f9858a08db0e184a68%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C638119269715896653%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=cO%2Bl9ZNMZQjQ604sd3TUwLgIZppehqnaxAQVPRvqPkI%3D&reserved=0
> <
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftc39.es%2Fprocess-document%2F&amp;data=05%7C01%7Cborg%40adobe.com%7C1ad998daefba43f9858a08db0e184a68%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C638119269715896653%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=cO%2Bl9ZNMZQjQ604sd3TUwLgIZppehqnaxAQVPRvqPkI%3D&amp;reserved=0>
> for description of their process stages.
> >>
> >> Here's the last discussion in TC39, from 2017:
> >>
> >>
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Ftc39%2Fnotes%2Fblob%2FHEAD%2Fmeetings%2F2017-05%2Fmay-23.md%2316ig-float16-on-typedarrays-dataview-mathhfround-for-stage-1&data=05%7C01%7Cborg%40adobe.com%7C1ad998daefba43f9858a08db0e184a68%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C638119269715896653%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=ZjJXIXO4oJNDwg57AJPpmbiZuPh8est%2Fix%2Bc9AvGoyM%3D&reserved=0
> <
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Ftc39%2Fnotes%2Fblob%2FHEAD%2Fmeetings%2F2017-05%2Fmay-23.md%2316ig-float16-on-typedarrays-dataview-mathhfround-for-stage-1&amp;data=05%7C01%7Cborg%40adobe.com%7C1ad998daefba43f9858a08db0e184a68%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C638119269715896653%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=ZjJXIXO4oJNDwg57AJPpmbiZuPh8est%2Fix%2Bc9AvGoyM%3D&amp;reserved=0
> >
> >>
> >> and discission prior to that:
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fesdiscuss.org%2Ftopic%2Ffloat16array&data=05%7C01%7Cborg%40adobe.com%7C1ad998daefba43f9858a08db0e184a68%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C638119269715896653%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=uxJP5MclogKptNG4rLYdvhrF5RWpSuKjGyZAQF8p8zA%3D&reserved=0
> <
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fesdiscuss.org%2Ftopic%2Ffloat16array&amp;data=05%7C01%7Cborg%40adobe.com%7C1ad998daefba43f9858a08db0e184a68%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C638119269715896653%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=uxJP5MclogKptNG4rLYdvhrF5RWpSuKjGyZAQF8p8zA%3D&amp;reserved=0
> >
> >>
> >> There were open questions, can we help answer them to move the proposal
> forward?
> >>
> >> Thanks,
> >>
> >> Chris
> >>
> >> -----Original Message-----
> >> From: Pierre-Anthony Lemieux <pal@sandflow.com <mailto:pal@sandflow.com
> >>
> >> Sent: 08 February 2023 18:59
> >> To: public-colorweb@w3.org <mailto:public-colorweb@w3.org>
> >> Subject: WHATWG comments re: Float16Array + HTML Canvas
> >>
> >> Good morning/evening,
> >>
> >> FYI. See the comment at [1].
> >>
> >> [1]
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fwhatwg%2Fhtml%2Fissues%2F8708%23issuecomment-1423026968&data=05%7C01%7Cborg%40adobe.com%7C1ad998daefba43f9858a08db0e184a68%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C638119269716052885%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=e9RJQV0LSpydxks9jCbge08HuieApEC9Kyd%2FSIlAm8I%3D&reserved=0
> <
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fwhatwg%2Fhtml%2Fissues%2F8708%23issuecomment-1423026968&amp;data=05%7C01%7Cborg%40adobe.com%7C1ad998daefba43f9858a08db0e184a68%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C638119269716052885%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=e9RJQV0LSpydxks9jCbge08HuieApEC9Kyd%2FSIlAm8I%3D&amp;reserved=0
> >
> >>
> >> I suggest we reply.
> >>
> >> Below is a first pass at such a reply:
> >>
> >> """
> >> - the objective is to achieve bit depth greater than 8 bit in Canvas,
> which is needed for native HDR imagery, among other things. This is needed
> today.
> >>
> >> - the suggestion to add support today for Float32Array today was with
> the understanding that support for Float16Array could not be added today
> because it required a change in JS
> >>
> >> Is there a concrete timeline for Float16Array, which would cause the
> Color CG to revisit its recommendations?
> >> """
> >>
> >> Please provide feedback by Monday COB.
> >>
> >> Best,
> >>
> >> -- Pierre
> >>
>
>
>
>
>