Auto exposre/histogram fooled by dust?

[DaveO]

Hi,

My second post on my experiments with SIlverfast and my V750.

I scanned a negative that had some dust spots on it and I noticed when I locate the brightest point of the image by clicking the relevant button on the toolbar the red cross hair selects the dust spot as it is pure white.

This not much use as I will want to remove this with Digital ICE later but in the meantime it may well be giving a false impression of the brightness range of the image. Could this mean an incorrect result with Auto Exposure?

Is there a way around this other than manually selecting what I think is the brightest part of the image?

And can I get the pure white dust spots to be disregarded when doing auto exposure?

Thanks,

Dave

[LSI_Morales]

Dear Dave,

Could this mean an incorrect result with Auto Exposure?

Most likely, the white spots will be regarded in the calculation. It is pretty much like the exposure meter in your camera, it does not see the image itself, it just sees light reflection, in the case of the software it will see the amount of light interpreted in the histogram value.

Is there a way around this other than manually selecting what I think is the brightest part of the image?

Well, you can mark the white point yourself using the "white, black and grey point" tool (see next pict.)

White, Grey, Black point tool

white_black_point_tool.jpg (21.27 KiB) Viewed 1287 times

can I get the pure white dust spots to be disregarded when doing auto exposure?

Negatives film stripes are prone to get very small craquelures, which are easily detected because those spots affect the orange mask as well, for that you will find the Auto-Tolerance slider in the Negafix window.

Slides do not present this characteristic, hence such spots are easily mixed within the histogram information of the image. This can not be avoided (think of it as the exposure meter of the camera, you would not be able to tell the exposure meter to disregard the whitest points).

Cheers

[DaveO]

OK, thanks for the reply.

Dave

[LSI_Morales]

Dear Dave,

My pleasure

Regards