When downsizing an image, the file size increases. Why?

[FrankC]

Hello, 

 

I looked under Frequently Asked Questions and searched with <"file size" (bigger OR increases)>, but didn't find an answer. This is my question: 

 

I have a .jpg image of 1600 x 944 which is 290 kB. When I downsize it to 1000 x 590 and keep it at 100%, it increases in file size, namely to 399 kB. Why is that? And how do I downsize it so that the file size gets smaller proportionally?   

[Ego Eram Reputo]

How about using the Quality slider? The less detail, the smaller the file.

 

Also try the 4:2:0 (Best Compression) option (Chroma Subsampling).

[FrankC]

4 hours ago, Ego Eram Reputo said:

How about using the Quality slider? The less detail, the smaller the file.

 

Also try the 4:2:0 (Best Compression) option (Chroma Subsampling).

 

I need to keep the quality the same, so I have to keep it at 100%. And 4:2:0 results in a file size of 379 kB. Slightly less, but still a significant increase. When I use Paint, the standard Windows program, these problems do not occur. Any ideas?  

[Rick Brewster]

MSPaint generally saves at a very low quality, IIRC.

 

It's not surprising that an image saved with a lossy compression algorithm, like JPEG, would increase in size when trying to re-save at a high quality setting. Lossy compression actually increases the visual complexity of the resulting image (from the computer's point of view, that is) and makes it harder to compress, especially for lossless codecs (like PNG), but also sometimes for lossy ones (like JPEG).

[FrankC]

17 hours ago, Rick Brewster said:

MSPaint generally saves at a very low quality, IIRC.

Not that I can see, and if I can't see it in the images of the said sizes, my site visitors will not, either. 

 

The rest of your answer would indeed explain what is happening, which was my first question. Thanks for that. And with MS Paint I can resize in a way that I like. But I'd still like paint.net to do it the same way, because I prefer to have to use just one program for all my image editing. Is there a Feature Request possibility for paint.net, that you know of? 

[null54]

19 minutes ago, FrankC said:

The rest of your answer would indeed explain what is happening, which was my first question.

 

Paint.NET may also be adding EXIF metadata to the JPEG file it saves.

You could try the following plugins, which may produce a smaller image than the built-in JPEG encoder.

 

https://forums.getpaint.net/topic/118213-mozjpeg-filetype/

https://forums.getpaint.net/topic/25369-optimized-jpeg-filetype/