That is in fact, what I've been doing.
Only 20 MB?? I thought 50 or something. Each file has to be less than 2 MB, but the number of files aren’t limited, are they?
i've seen some folks with super long pages/updates but they're just mega sliced up to compensate
honestly this one makes me cry cuz it's true jpegs always seems to save way smaller than pngs but i hate jpg/jpeg 
Yeah I mixed it up with webtoon sizes--so webtoon is max 20mb I think, and on Tapas it's 40 updates, but it's max 2 mb each so it ends up being less overall.
Before CSP updated with the webtoon splicing feature, I would put it through croppy -- which would resize, splice, and convert the pages. Now I just use the CSP feature, and it does what it needs to do based on the parameters I give it.
And if it doesn't fit in terms of MB, I just throw everything through tiny.png or tiny.jpg. I've got three comics on Webtoons with 60+ panels each update -- and I made them fit. Haven't tried them with Tapas yet, but with the methods I have, it shouldn't be a struggle.
Important to note: the parameters listed for both sites are the max. I'm pretty sure as long as it's equal to or less than those parameters, it will take. So I can also imagine some people working with, say 600 px or 700 px as the width.
Probably 8-bit png/gif format, or with lots of blank flat spaces. If the page's black & white or with only few color palette, they can compressed it to a very small color table to keep the filesize down.
What always works for me is on photoshop. If you "save for web" - although in the new version of photoshop it might be under "extract - save for web", you can make a compressed version of your image. I generally make sure the saved file is set to "jpeg", not "gif" which I find it automates to, and then I just reduce the image size by like 25% or 50%. Any change in quality is amazingly minimal, unless you really zoom in. I've gotten images from like 15 mb to like 1, or less than 1, without noticeable quality change.
This might be an obvious tip or something - anything I know how to do in photoshop is self taught so I'm sure this could be a known method...
Hmm, don't have answers but this prompted me to try out my upcoming project to make sure it would work 
First episode is on the longer side at 27 panels, managed to fit comfortably on Tapas in 17 files (so still 23 to go if needed) but cut it close on Webtoons at 15/20 MB. Exported as PNG at 300 dpi via CSP's tool fwiw. My concern on webtoons now is that that was sans a map that I want to include and the "plz like/comment/subscribe" bit so I hope I don't run over the 20MB limit there might have to do the map as a JPEG lol
Yep, this is what I use, Save for web. I really wonder if it's like...an amount of colors thing, like maybe I have a toggle on my Save for Web that other people have turned off? Who knows?
@jimena Yeah that's a suspicion I've had, that white space doesn't actually add much to the MB amount of a picture (I don't like using white space in my scroll comic bgs, so I use colored gradients). So I did a test on that theory and saved a rainbow gradient and also saved a plain solid color of the same dimensions. What I found out is that the gradient is 13 times the file size of a plain background (It is a rainbow--so it may be smaller if it's not as contrasty or saturated). Then I was like--well what about a flat color background, are all flat colors the same size? And yes, all colors are the same size so long as it's flat, whether it's white or black or gray or purple.
So the more details you add to your comic with gradients and saturation, the bigger it gets, which makes sense and I should've figured that was the case--but I didn't realize that those gradients are probably why my files are getting so massive in comparison to stuff that does a plain background like white or gray.
fwiw I found similar results with the aforementioned test that I did last night. Most of the episode I tried out could have actually fit in Tapas' 940 x 4000 size limit, but I ultimately went down to 940x2000 for most of the episode (after trying 3500 tall as well) because a few chunks with semi-transparency were driving the file size up just over 2MB. Two panels like this were the main culprits:
A few gradient lighting effects in place, and the soft edges = file size bust 
The worst offender, though, was this panel:
The background here was a manual gradient made by blending together a textured watercolor brush... I had to split the 940x2000 chunk that contained this in half again to 2x 940x1000 to beat the file size limit I'm not not going to use this effect when appropriate in the future, but it's definitely food for thought. Where Tapas allows up to 40 files it's not a big deal, but using too many of that type of BG could sink and episode on webtoons...
Webtoons has a different limit for their Originals 100% (maybe no limit at all, who knows). It would make sense if Tapas works the same.
@rhonder Yeah, I use these fancy effects all the time, I freakin love em. I guess it gives me an excuse to make shorter updates and never feel bad about it, haha.
If you use the slicing tool on photoshop or webtoon export (i think thats the name) on clip you can slice your panels in really small sections then save in high resolution JPEG (since its the smaller size format compared to PNG). The slicing/export tools save each section automatically in one go and don't worry about cutting panels in half, tapas + webtoon sticks them together without any spaces.
My comic is really colourful with lots of shading and text, i sometimes have 25-30 panels but I've never reached the MB limit. The size for each slice for me is 800x1200 and doing that lets me save it in the highest resolution. I'd rather slice in small sections rather than lose any resolution or change my art in anyway.
Edit to add: Are you saving PNG or JPEG? Png file sizes can be huge which would explain why you might reach the MB limit.
