converting 1080 to 720

Midyin

So I'm using photoshop to reduce my "Full HD (1920 x 1080)" down to "HD (1280 x 720)". I'm doing this because I been told that reducing the image scale like this will make it look smoother/better.. 

My question is, What should I set the resolution to? (the defult is 300 pixles/inch)

Will the image look better if i increase that number, or change it to pixels/cm? (I assume cm = centimeters)

If I set that number too high will it make the image look worse?

Richard Haseltine

If you have noise in the image then downsampling will help t smooth that out, but for that to make sense you have to ender larger than you need so that the downsampled version is the size you want.

Set PPI to whatever you want - when setting the image size in pixels it has no meaning (obviously if you set the size in inches, or another physical unit, you have to tell the editor how many pixels to pack ito each inch).

Dim Reaper

It really depends on what you want to do with the final image.

Reducing a rendered image in the way that you describe should eliminate any "fireflies" - the bright pixels that you can get when an image has not fully rendered, and reduce the graininess of the image.

The DPI is mainly for printing - the 300dpi that you mention would mean that your 1280 x 720 image would print at just over 4.2 x 2.4 inches.  If you are printing the image, you want the dpi at 300, and the image as large as possible.

However, if you are simply uploading your image to an online gallery then the dpi is much less important than the image resolution. I sometimes resize images in the eay that you have mentioned, and my default DPI in photoshop is 96 DPI and I'm happy with the results.  For online only use, 72dpi is fine.  For printing, 300dpi.  Choose a number between those and don't worry too much about it if you like the final image.

There is an article here that goes into more detail: http://www.rideau-info.com/photos/mythdpi.html

fastbike1

Of course just having proper lighting and rendering for convergence will manage the same thing even without the denoiser. Darl scenes will alswys be more problematic. It is better to have enough light to converge the render then use tonemapping to get the look you want.