Histogram and Cache

[Rex]

Hi there,

I have only recently started shooting digitally. Process the NEF files with ACR, ensuring that the histogram is not clipping and open into CS3.

The histogram will look pretty much like the ACR histogram, but if I click the cache warning triangle, there is severe clipping.

As all my adjustments are with the histogram open and I can see what is happening (I think), what exactly is the cache warning? If refreshing by clicking on the cache triangle and the histogram now shows clipping, what am I looking at when adjusting the image with the histogram open?

Or to put my uncertainlty another way, is the histogram showing what I am actually doing/saving or is the cache refresh showing what is being saved?

Rex

[Medley]

The histogram is normally drawn from one of the cache levels Photoshop uses to speed up redrawing processes. You can control how many cache levels Photoshop uses in the Preferences panel. Histograms drawn from an image cache are based upon a representative sampling of the image. When you click on the cache warning ( or just double click the Histogram), Photoshop redraws the histogram from the present document state, sampling every pixel to do so. It is the most accurate representation of the current status of the image.

- Joe U.

[Rex]

Thanks for your reply.

And so to the next question! When I save an image, presumably the current histogram / cache state is also saved. So why when I next open that image, does my cache level read 4 ( I have it set to that) but when I double click the histogram, it refreshes cache level 1, when I have not done any adjustments yet? It seems that what is saved is not the correct histogram, or am I missing something?

Rex