When I'm in In Design (CS6 although I don't think it makes a difference in this case) I have my layout set to web and I'm using pixels as my measurement tools. However when I copy and paste an image into Photoshop (CS6) it says the image is much larger than what appears in In Design. Next when I used the export HTML function in In Design I looked at my folder of images and all of the images were the wrong size (not the same size as what Photoshop or InDesign said they were) and not the same size as what was originally in In Design.
Why are my images all different sizes?
If I make my document for a certain size and I export shouldn't In Design save the images at the size I've specified within my document?
Any help on this topic would be much appreciated.
"Pixels" as a measurement unit in InDesign are a hack, a kludge, and Not A Real Measurement Unit. That's the entire story. They are exactly equal to points but with the suffix "pt" replaces with "px". (Also some of the drawing tools do some rounding.)
The entire point (so to speak) of "pixels" is worthless if you do not provide a translation into screen space in the form of a target resolution. In Photoshop you set this in the very same dialog: you can enter a size in inches or centimeters and a resolution, and PS calculates the size in pixels, and vice versa.
However when I copy and paste an image into Photoshop (CS6) it says the image is much larger than what appears in In Design.
When you cut and paste from ID to PS the object's pixel dimensions, shown in the Transform panel, are used. So by default a 500 x 300 pixel frame pastes as 500 x 300 pixel vector smart object into Photoshop:
InDesign CS6 has changed the way the page's Zoom percentage is displayed. Prior to CS6 a 100% zoom was the same as Photoshop's (a 1:1 pixel ratio), now ID detects your monitor resolution and displays the actual print size when the Zoom is 100%.
See this thread:
There's an AppleScript at the end that lets you restore the zoom percentage to the pre CS6 method. After running the script 100% in the 2 programs diplays the same like this: