PNG to JPG conversion

[Fat_Frank]

Hi there

Please can someone help me to understand the optimum settings for the above, as I have what appears to be an anomaly:

I have a 1500x15000 PNG which I'm converting to a JPG of the same size. The original PNG is 1.69mb and my JPG conversion is 760kb: however if I convert and resize to 1400x1400 the resulting JPG is 963kb.
I have save quality set to 100% and all of the boxes checked, except for three: the first two (progressive & grayscale) and the last but one (try to save with original JPG quality).
Any advice greatly appreciated.

[Bhikkhu Pesala]

Without seeing the original PNG we would be just guessing what the problem is.

[Fat_Frank]

Without seeing the original PNG we would be just guessing what the problem is.

It seems to happen with any PNG that I convert to a JPG of the same size. Try this one as my most recent example:

https://f4.bcbits.com/img/a1173628751_1

[Bhikkhu Pesala]

Use the Image information button to see the number of colours before and after scaling. Scaling the image from 1,500 to 1,400 more than doubles the number of unique colours.

With photo like this, there is little to be gained by using the highest possible quality. Reduce the slider to 90% or as low as 75% and see if you can spot the difference without zooming in close.

Better PNG compression could reduce the file size slightly. Reducing the number of colours would reduce it by half.

[Fat_Frank]

OK, I'll give your suggestions a try. Thanks for your help.

[Bhikkhu Pesala]

With that particular image, you can crop it rather than resizing it.

[Fat_Frank]

With that particular image, you can crop it rather than resizing it.

I could, but I want the best possible size variants of the original PNG for uploading to the Album Art Exchange.