Re: Shrinking a picture --- and it becomes blur !!

hsyq8xg@[EMAIL PROTECTED]
 wrote:
> Sorry for this late reply.
> 
> 3 example online:
> 
> A. www.PenangA1.com/png/1K.PNG
> 
> B. www.PenangA1.com/png/4K.PNG
> 
> C. www.PenangA2.com/png/ORI.PNG

All three time out from here long before they download.

> If you take a look at Picture C (ori.png), it's from the original
> drawing ( resolution: 4096 X 3072 ), with file size of 37MB, in BMP
> format. In Picture C you can see patches of green leaves distinctly,
> arising from the brown wall.
> 
> Picture B represents a screenshot fragment of the 37MB drawing as my
> desktop wallpaper (1024 X 768). As you can see from Picture B,
> although much smaller than Picture C, the patches of green leaves are
> still separated from the brown wall.
> 
> However, if you look at Picture A ... the patches of green leaves
> kinda melt into the brown wall behind it. Picture A was from a
> fragment of a 1024 X 768 picture (JPG format) that I shrunk from the
> original 37 MB BMP drawing. When I shrunk it, I use 100% JPG quality,
> with the "Lanczos" option.

> Any comment ??

Which JPEG encoder did you use?

And more critically what chroma subsampling - the default used for 
photographs does tend to compromise line art images.

If you override the chroma subsampling to save YCrCb with 1,1,1 ratio 
then you may get better fidelity (although a larger filesize).

Fundamentally you cannot get around the fact that when the image is 
downsampled the new image pixels get bigger and contain colours that are 
some weighted average of the original pixels.

Regards,
Martin Brown
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