Newbie question on resizing and impact on quality and file size

[Mangolife]

Hi,

Thanks for taking the time.  My challenge is in finding images that look high quality on desktop and mobile devices while having the file sizes remain low so that it doesn't slow down page load and also use up a lot of space on my server.  I was surprised to find that when I resized a 6000 * 4000 to 600 * 400 that the quality appeared reduced.  I'm thinking this is simply because it is a physically smaller image that I'm looking at on the same size screen.  At least that makes sense to me.

I also understand there is something called resampling and I should select bilinear when i resize, but this still made no difference.

Which brings me back to the challenge of how to select images (I'm using Unsplash) to get images that look good on desktop and mobile but also still have a small file size.

Appreciate any advice or resource you can point me to so that I can learn how to select an image and create a workflow that makes this an easy process.

Thanks again.

[John Rostron]

6 hours ago, Mangolife said:

when I resized a 6000 * 4000 to 600 * 400 that the quality appeared reduced

Yes, it would. Resizing will involve resampling. Try using one of the Lanczos 3 resampling algorithms. They can often result in a better quality photographic image (though not for a graphic image). 

You might also apply a judicious amount of light sharpening to your final image.

John

[R C-R]

11 hours ago, Mangolife said:

I was surprised to find that when I resized a 6000 * 4000 to 600 * 400 that the quality appeared reduced.  I'm thinking this is simply because it is a physically smaller image that I'm looking at on the same size screen.

It is because there are fewer pixels in the reduced size image, not because of its physical or display size. "Pixel" is short for "picture element." It is so named because it is the fundamental logical unit of picture information in digital images. Reducing the number of pixels in a digital image means reducing the amount of information in it -- IOW, lowering its quality.

There is no way around that, but as John mentioned, using different resampling algorithms can affect the visual quality loss.

[Mangolife]

Thanks both.  I will try the lanczos 3 resampling.  Looks like I will just have to experiment to see what works that also doesn’t make the file size too big.