Images grainy in Photoshop

[carolcaracol]

I noticed from my last submission to Behance that my design appeared grainy in certain parts, so I decided to do some tests and found that it's not just in behance, from the moment I save the image it gets grainy no matter where.
The problem is, on photoshop it looks perfectly normal till I save and preview it... Here some things I already did:

- My image is below 1mb
- It's in RGB
- It's PNG 
- I already turn off Nvidia's 3D sharpening
- My cache is set to 6
 I know there are many topics with the same issue but they just didn't fix it, also there's nothing to do with the scale of the image (100%, 50%) they all look the same. Can somebody help me, please? I really don't know what to do. 😞

[Kevin Stohlmeyer]

This has to do with how you are saving your files. For the JLF example you show your pixel dimensions as 1200 x 5693 at 300 ppi. Thats a base 19.5 mb file. If you are saving down to under 1 MB you are either downsizing your image dimensions or resolution significantly when saving your png file format. 

That is what is causing the saved file to look so poor. 

What settings or how are you saving these files out of Photoshop?

[carolcaracol]

Thank you for replying. Ok so, about JLF the image is a whole "banner", so what I did was downsizing these files in a website that fulfill it and deliver as the same format as I saved (all of PNG). However, when I upload the banner on Behance or any website without downsizing it looks the same... As you said is a problem of how I'm saving them, yet even before saving is already 4.27 mb..
I saved the files in many different ways, the first one I basically chose Save As... and selected PNG, then I was asked if I wanted the file as Large, Medium or Small (first print) I selected Large. 
Then I tried Save for Web, chose PNG-24 (also tried PNG-8, but looks worse) I also saved as a Large file. 

 
Cor do Monitor = Monitor Color

[Kevin Stohlmeyer]

When you use save for web it is down sizing your images to 72 ppi thereby causing the image degredation.

Use save as and try a jpg format - I do not see transparency in these images so PNG is not needed.

[Per Berntsen]

The image at the bottom (Prancheta 2) is viewed at 249% in the Photos app, at that magnification any image will look bad. At what magnification are you viewing the same image in Photoshop?

For the record, the PPI value is irrelevant for screen viewing, and does not affect image quality.

PPI is optional metadata used for calculating print size.

Pixel dimensions divided by PPI = Printed dimensions in inches.

Save for web will strip out the PPI value, since it's not required for screen viewing.

If you open the image in Photoshop after Saving for web, Photoshop will assign a PPI value of 72, because it's needed to display type correctly, and to be able to display rulers with physical dimensions.

The value of 72 is arbitrary, and could be anything, but happens to be 72.