how to reduce the kb size of an image

Where will the image be used for? That is a very important question.

In the present answers I don't see 24/32-bit PNG mentioned as a non-lossy compression format (contrary to JPEG) if you want to use the image for web purposes and need transparency?

velorp33326544 wrote: how to reduce the kb size of an image

Look in your Status bar. There are two sizes (if you have it set to the default Document Sizes). The first is the size without Layers and Alpha Channels. If you can reduce the number of layers by merging or flattening them and delete any saved selections in the Channels panel, that is where I would start.

A CMYK image will be larger than an RGB image due to the extra color channel. Grayscale is smaller for the same reason—one color channel.

Then do what others have suggested. Reduce the actual size of the image. A jpeg is smaller file, but it is lossy, and is a one-time save. It also does not support transparency.

Hello, you can choose to reduce the size of the image as Joseph suggests, or choose a compressed file format. The lighter file format for a picture with many colors is JPG. You can choose from the main menu File/Save as and then choose JPG from the drop down menu of the Save as Window. Once you choose JPG you can set the amount of compression, have a preview of the final aspect your picture will have (JPG compression decrease the quality), and see the final size your file will have.

Please note: with JPG you will loose the layers and the quality will decrease. If you need to preserve layers or have a high quality I'd suggest you to use TIFF and LZW compression.

A simple method is to simply reduce the file size by using Photoshop's Image Size menu

Go:  Image > Image Size and reduce the dimensions or resolutions.  Make sure that the Resample box is check.

I hope this helps.