Why does the contrast and sharpening of an image increase when I resize a processed image? For example I have a file that is 4165 x 3087 pixels per inch that I have reduced to 1400 x 1038 pixels per inch that the contrast and sharpening have increased so mush to really damage the quality.
There are several variables here:
1. The numbers that you posted reflect a reduction in pixel dimensions, e.g. 1400 px x 1038 px.
The before and after values which you posted also do not reflect a consistent aspect ratio. Somthing has gone wrong. See below for suggestions.
2. The resolution, not stated, is a value expressed in px/in.
Go to Image >resize>image size and in the dialog you can make appropriate changes. Be sure that "Constrain Proportions" & "Resample Image" are checked in the dialog.
3. The contrast/sharpening may appear altered to the eye as you reduce the image dimensions. Think of print on a ballon which becomes indistinct with inflation and reverts to sharper text with deflation.
Again, you don't state the resolution of the before & after.
4. As to a very pragmatic work-flow, you should consider the crop tool. On the tool's option bar one can select from several defined crop ratios and "no restriction." Also the resolution (px/in) can be specified.
The rule of thumb for printing is 240-300px/in. For web work, 72 px/in is ok.