Hijsachs wrote:Based on the workflow you are describing, you may be misinterpreting comments about bit depth. If you start with a 24-bit image, converting to 48-bit does not add any information to the image or confer any benefit when applying curves. The benefit of 48-bit images comes mainly if you start with a 48-bit image such as you might get from a raw camera file or a scanner. Such an image does have information beyond what is in a 24-bit image and that information can help reduce posterization when applying curves, notably where the slope of the curve is steep. Once you are done making tonal modifications, you lose very little by converting at that point to 24-bit.
There are some very minor benefits to converting a 24-bit image to 48-bit in that sharpening and blurring may be slightly smoother, but it is unlikely you could see the difference by eye. Certain color space conversions may also be a little less likely to posterize in 48-bit color, but again the effect should be very minor in most cases. Personally, if I have a 48-bit image I tend to leave it as 48-bit and if I have a 24-bit image I leave it as 24-bit.
The difference in histograms you are seeing is apparently due to a change I made in PWP 7.0 in the way 8-bit images are converted to 16-bit images (and 24-bit to 48-bit) in that a small amount of random noise is added to each channel during the conversion (this is called dithering) which makes for a slightly smoother looking image. In earlier versions of PWP, it the operation you describe in your post produces more or less identical histograms. The bumpiness of the histogram actually indicates less posterization in this case.
Does the 24 bit image hold it's quality when there are a nr of curves used after each other?
Alain