Because I have nowhere else to write this down. I've been very interested in the approach to matted widescreen in animation for quite some years now.

Matted widescreen was introduced to US cinemas in 1953, and the road to widescreen in animation was seemingly bumpier than it was live action. Famous was there day one, no doubt due to Paramount's great interest in widescreen, pioneering "flat" or "matted" widescreen with the release of Shane. (So I assume.)

Perhaps the most bemusing of the studios to transition to widescreen was Warner Bros. I had read Eddie Selzer or someone else at Warners had announced shorts compatible with a 1.75:1 ratio in 1954, but absolutely no cartoons were actually consciously staged for widescreen until around 1960.
What the first widescreen-compliant short from Warner was I have no idea, but anywhere from Wild Wild World (prod #1529) to Goldimouse and the Three Cats (prod #1535) were my guesses through observation alone. Layout art for Martian Through Georgia and Louvre Come Back to Me confirm that widescreen staging was in full swing by at least 1961.
The early 60s Warners are decently laid out for widescreen, with only a few hiccups along the road. I find they look quite nice. DFE and the Bill Hendricks studio may have grappled a better understanding of working for the ratio.

Lantz took an odd approach to widescreen. I'm not sure if their cartoons were laid out for matted widescreen, but at some point they started making sure they were safe in a 1.19:1 ratio, just so Universal could offer projectionists to screen them in Scope! Yes, they'd look very stretched out and ugly. Evidently, they didn't care.

There are always oddballs and outliers. It would appear that in the mid-60s some of the New York studios just gave up making sure a cartoon could fit in a wider frame. (Bakshi's Terrytoons, for instance?) That's something I'd need to look further into. This was also a point where they'd be releasing TV cartoons like Deputy Dawg to theaters.
DePatie-Freleng for United Artists seemed to be inconsistent. I've seen a layout drawing from the Tijuana Toads series with widescreen camera guidelines, but looking at the screenshots for Hoot Kloot on this site seem to be strictly Academy ratio. The 1978 Pink Panthers, while released to cinemas, were made for TV first.

Even late into the game, things could be weird. Filmation's Pinocchio (1987) was evidently staged for 1.66:1 long into the point where 1.85:1 had become the de facto standard. Shinbone Alley (1970), a film staged for widescreen, had its ratio listed as "1.33" in its pressbook. Gene Deitch's Tom and Jerrys were made for Academy ratio, but MGM recommended they be screened in 1.75:1 anyway. (Even if the title cards on those went out of frame.)

I do have to wonder if the big misstep with the Looney Tunes Super Stars DVDs in the early 2010s has influenced any companies on presenting animation in the future. I wager if Warner Archive ever gets around to the 50s Popeyes, the ones released from '54 onward will be presented "open" in 1.37:1.
As it stands, the Chuck Jones Tom and Jerrys, I find so nicely staged for the 1.75:1 ratio that I can't stand looking at them "open." The MGM studio then actually had widescreen framing printed on every sheet of paper in blue!

Because I have nowhere else to write this down. I've been very interested in the approach to matted widescreen in animation for quite some years now.

Matted widescreen was introduced to US cinemas in 1953, and the road to widescreen in animation was seemingly bumpier than it was live action. Famous was there day one, no doubt due to Paramount's great interest in widescreen, pioneering "flat" or "matted" widescreen with the release of Shane. (So I assume.)

Perhaps the most bemusing of the studios to transition to widescreen was Warner Bros. I had read Eddie Selzer or someone else at Warners had announced shorts compatible with a 1.75:1 ratio in 1954, but absolutely no cartoons were actually consciously staged for widescreen until around 1960.
What the first widescreen-compliant short from Warner was I have no idea, but anywhere from Wild Wild World (prod #1529) to Goldimouse and the Three Cats (prod #1535) were my guesses through observation alone. Layout art for Martian Through Georgia and Louvre Come Back to Me confirm that widescreen staging was in full swing by at least 1961.
The early 60s Warners are decently laid out for widescreen, with only a few hiccups along the road. I find they look quite nice. DFE and the Bill Hendricks studio may have grappled a better understanding of working for the ratio.

Lantz took an odd approach to widescreen. I'm not sure if their cartoons were laid out for matted widescreen, but at some point they started making sure they were safe in a 1.19:1 ratio, just so Universal could offer projectionists to screen them in Scope! Yes, they'd look very stretched out and ugly. Evidently, they didn't care.

There are always oddballs and outliers. It would appear that in the mid-60s some of the New York studios just gave up making sure a cartoon could fit in a wider frame. (Bakshi's Terrytoons, for instance?) That's something I'd need to look further into. This was also a point where they'd be releasing TV cartoons like Deputy Dawg to theaters.
DePatie-Freleng for United Artists seemed to be inconsistent. I've seen a layout drawing from the Tijuana Toads series with widescreen camera guidelines, but looking at the screenshots for Hoot Kloot on this site seem to be strictly Academy ratio. The 1978 Pink Panthers, while released to cinemas, were made for TV first.

Even late into the game, things could be weird. Filmation's Pinocchio (1987) was evidently staged for 1.66:1 long into the point where 1.85:1 had become the de facto standard. Shinbone Alley (1970), a film staged for widescreen, had its ratio listed as "1.33" in its pressbook. Gene Deitch's Tom and Jerrys were made for Academy ratio, but MGM recommended they be screened in 1.75:1 anyway. (Even if the title cards on those went out of frame.)

I do have to wonder if the big misstep with the Looney Tunes Super Stars DVDs in the early 2010s has influenced any companies on presenting animation in the future. I wager if Warner Archive ever gets around to the 50s Popeyes, the ones released from '54 onward will be presented "open" in 1.37:1.
As it stands, the Chuck Jones Tom and Jerrys, I find so nicely staged for the 1.75:1 ratio that I can't stand looking at them "open." The MGM studio then actually had widescreen framing printed on every sheet of paper in blue!

I actually liked the Super Stars widescreen. Seeing them look like "movies" was a treat for me.

---

I also enjoy seeing post-1953 films matted, but I think it also pays to see the "whole picture" (current prints of 101 Dalmatians are presented open-matte, but the features from The Sword in the Stone onward are all matted). Then again, I've seen some film scans of trailers for Disney features that reveal things like background edges, cels not painted below a certain point, and even register pegs. I think there would be a discussion of how far is too far in terms of matting.

Also, with many pre-1953 cartoons being reissued with open-matte title cards after the widescreen revolution, it can be hard to map the change to when newer cartoons started using them. I know that the Goofy short How to Dance (from the 1952-53 season) was originally released with Academy titles, but the next one, How to Sleep (from 1953-54) had "open-matte" titles with the redrawn Goofy headshot seen on most others today. On another note, MGM's Mice Follies, their first for the 1954-55 season, seems to be one of the last with Academy titles, and it opened with a unique version of the 1954 "Tom and Jerry" series title.

The original pressbook for Dalmatians dictates that the ratio is 1.37:1. Whether it was staged for widescreen is beyond me. Heck, I've never seen any layout pages for Disney features with an indicated camera field ever (except for Great Mouse Detective). It's Tough to Be a Bird is staged for Academy, even though it was incredibly late in the game. Despite this all, the 60s Disneys onward are definitely conscious of widescreen and the pressbooks recommend 1.75:1 all the way up to The Fox and the Hound. Oliver and Little Mermaid were hard-matted to a widescreen ratio.

The case with Warner Bros is slightly a bit strange. Evidently, a whole slew of the last season before the disjointed one-- where the shutdown took place-- had been finished in Academy. A preliminary cel exists for the credits to Stop, Look, and Hasten!, using the Academy ratio.

From A to Z-Z-Z-Z, despite using the opening cards with the newer aspect ratio, has title cards that were clearly meant for an Academy screen.

They also interestingly filmed new cards for the opening, but never replaced the end footage until it was time to change the ring color to magenta.

Evidently, the decision to move to widescreen was very hasty. The cartoon revues copyrighted from 1953 give the indication that they were all going to be originally presented in Academy. For unknown reasons, the trailer for Bugs Bunny's Cartoon Festival features a clip of Lumber-Jack Rabbit with a much different, more detailed background. I wonder if it was shot just for that.