loss of quality when downsizing picture

[ImmuneEntity]

I'm feeling really stupid right now because I can't figure this out. I'm trying to resize some facesets. I have to downsize them to get them to fit properly. Here's my issue:

Can anyone tell me what the heck is the difference between these two pictures??

http://i38.photobucket.com/albums/e127/ ... luxes1.png[/IMG]

http://i38.photobucket.com/albums/e127/ ... luxes2.png[/IMG]

They look the same to me! Except that one is 100x100 and the other is 98x98. However, the first one is 15 KB, and the second is 5 KB. When I resize the first one to 65x65, the quality seems fine. But if I resize the second to 65x65, it looks much worse. This is very troubling, because I have to do this for a few other images, and I can't replicate that same quality! Why is one 5 KB and the other 15?

I am using GIMP to do this. When I am editing the first image, at the top it says RGB, but the other one says indexed. I'm not sure what that means, but does that maybe have something to do with it?

 

[Ocean]

Essentially that. Indexed color leaves it as a few colors (Usually 256, 8-bit), and also does a nearest neighbor rescaling, which is a direct pixel scaling with no blending of the edges, which is good only for sprites and pixel art, and only when you're scaling by a factor of 2 (Unless it gets too small). Change it to RGB before rescaling and it should be fine. Once you rescale it, then change it to 8 bit.

RGB is 24 bit, and Indexed can be 8 bit (Though you can set it to have less colors, at least in Photoshop). Therefore, since indexed uses far less colors, the file size will be smaller.

 

[ImmuneEntity]

Ah, I see. That fixed it. Thank you for your help

 

[Tohsaka]

Well, you could resize the RGB one down, and index it to get the smaller size.

 

[ImmuneEntity]

Yes, that's what I've been doing now. Although the memory size of the image wasn't really my concern (I just didn't get why one took up 3x more space than the other). But I guess RGB does a much better job at downsizing than indexed.

 

[Tohsaka]

RGB contains all the colors, while Indexed only contains the colors used in the image.