Issues with Scaling Down Sai Images

[Obscura]

So, if I take my layered sprite and scale down in Sai:
quality = questionable

But if I export the layers into .pngs first and then scale down:
quality = much better

How do I achieve the higher quality of the first without taking about 3000 hours to export and scale down all the separate .pngs?

Photoshop seems to have a batch resizing function but there is no option for .pngs.

Is there a commercial program that maybe resizes batch files easily and automatically?

Or am I doing this a** backwards as I am normally inclined to do?

Thanks for any advice.

*I should add that exporting now is much easier because of Camille's suggestion to use Slicy (thank you forever). It's the resizing part or the task that is the challenge.

**Edit 2: I'm also seriously reconsidering the idea of working in such a large file size if my final sprites when I get reduction quality after resizing down?

[AxemRed]

I like XnView's batch image conversion function. You can even save the settings if you need to run it again.

[Obscura]

Much thanks for the speedy reply--checking it out right now.

[Obscura]

@AxemRed:
Thanks for the suggestion. The program's great. It's doing exactly what I need. Between Slicy and XNView you and Camille have saved me about 20 hours of time or more. Thank you again.

[nyaatrap]

Bicubic resampling (There is no resource what filter SAI is using. But from my eyes, it seems Catmull-Rom) causes aliasing and ringing when it downscales pixels overly at once.
http://www.imagemagick.org/Usage/filter/ is good resource to learn about resampling filters.
http://entropymine.com/imageworsener/bicubic/ is also usefull to know the difference among bicubic filters in various applications.
I use Mitchel with Xnview mainly.

[LateWhiteRabbit]

So, if I take my layered sprite and scale down in Sai:
quality = questionable

But if I export the layers into .pngs first and then scale down:
quality = much better

How do I achieve the higher quality of the first without taking about 3000 hours to export and scale down all the separate .pngs?

Photoshop seems to have a batch resizing function but there is no option for .pngs.

**Edit 2: I'm also seriously reconsidering the idea of working in such a large file size if my final sprites when I get reduction quality after resizing down?

I've used several different professional image scaling tools, programs, and plug-ins, and honestly, Photoshop's built in Image Resize is the best I've seen. Just pay attention to what resampling option you're choosing. (Photoshop will actually tell you what is best for what type of image.)

Photoshop can do batch resizing for .pngs if you create an Action to do it for you. Basically, in Photoshop an Action is a set of steps you do while the program records, then you can tell it to stop recording, then do everything you just did to an entire folder of images.

In my opinion, there is almost zero downside to working in a large file size, then reducing the sprites down. Almost all professional artists do this. Professional illustrators since the 19th century have worked larger than the final print product, then reduced it down. Comic book artists, even in the current digital age continue to do this. The final art you see in comic books and manga has been downscaled from the original pages. Even many video game artists are doing this now, painting textures much larger than the final product and downsizing afterward. They recognize this makes their job easier, but also provides higher resolution assets for an PC release, a HD patch, or a re-release in the future after computers and screen resolutions improve. It's rather cool when you think about it - like artists future proofing their work for times when better viewing is possible. Lots of Windsor McKay's original art boards were used at original resolution to print new books of his Little Nemo strips in a bigger and clearer format than was possible in the original newspapers.

Also consider a lot of anime is released in 1080p, and also 720p, or broadcast in 480p. ALL OF WHICH ARE DOWNSCALED. The original drawings (frames) are the equivalent of 2550x3300 pixels at 300 DPI. So even a 1080p anime has been reduced in size. And the picture still looks great, doesn't it?

This allows more detail, easier drawing and coloring, and everything looks better when made smaller. Lines are smoothed - mistakes and imperfections made harder to spot. Plus, if you need art for posters, magazine printing, box art, whatever, you have high resolution files to work from.

You just have to realize some programs suck at downscaling. (SAI is apparently one of them.) It is ALL about the resampling algorithm used, and the best one to use is going to change depending on the image details.

[Obscura]

@ nyaatrap
Thanks for those links! I was always curious about the differences between the different algorithms and what they mean...those are helpful breakdowns.

@ LWR
Yeah, I think rescaling was never a problem for me until I started trying to use SAI to rescale and then flipped out when practically all the details in my image disappeared. XnView is pretty simple to use and the image looks pretty good under the different algorithms I've tried so far, but when I get a chance I'll take a look at Photoshop actions. A lot of times I'll just keep away from PS if I can because I'm easily overwhelmed by all of its many, many options.
Thanks for the lesson.

[AxemRed]

Photoshop's built in Image Resize is the best I've seen.

It only does nearest/bilinear/bicubic which isn't exactly spectacular. None of these is particularly well-suited for downscaling more than a factor 4 (they all take a fixed number of samples 1x1/2x2/4x4). The popular lanczos filter is missing and there's no option to take gamma into account. I'd call Photoshop adequate, but not even above average in any way.

[nyaatrap]

Look at this entry: http://entropymine.com/resamplescope/notes/photoshop/ His research fits to my personal experience.
It explains why Photoshop is good in most cases, especially on photos, but never the best (In fact, this pixel shift is really annoying for me). You need to do multi-step resizing manually on most other tools (other than using Lanczos3 filter: it can resize down overly at once), like Photoshop is doing automatically.