If this video doea not address it nothing will! For EPSON

Started Mar 26, 2013 | Discussions thread
Hugowolf
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Re: Relative colorimetric vs perceptual
In reply to Fulvio Senore, Mar 28, 2013

Fulvio Senore wrote:

Perceptual changes ALL the colours in the image in a proportional way so that they lie in the printer gamut. This happens also if the image does not contain out-of-gamut colours.

Close but not quite right. The presenter does say that perceptual intents change all the colors in the image, but that isn’t so. Perceptual intents do compress some in gamut colors to make room for shifting out of gamut colors into the gamut, but they do not do that to all in gamut colors.

What perceptual intents do is highly dependent on their implementation, they are very proprietary. The perceptual intent from the Adobe CMM (color management module) could vary greatly from the one in the Microsoft CMM, but I have never come across one that would shift all in gamut colors. There is nothing proportional about it.

The other intents are well defined, but perceptual is basically a black art.

I stopped viewing the video after a member of the audience asked about rending intents and matte papers, at that point it was clear he didn’t know what he was talking about. Some may have stopped with the idea of using a towel or old pillowcase to cover the printer - short fibre cotton, I don't know if there could be anything worse.

What he talked about that immediately prior to that, about choosing relative colorimetric vs perceptual was actually sound. If you have no out of gamut colors, then there is no reason for choosing perceptual, unless that provides you with a more pleasing print. If you have an image with out of gamut colors that are different but close in hue and want to differentiate between them in the print, then it is worth trying perceptual if relative colorimetric would clip them to the same color. His example is over used, but still valid.

The most common problems lie in the saturated greens and oranges. (A reason why Epson UltraChrome HDR inks include those two colors.) Fall foliage, with lots of yellow-reds, where you want differentiation between different yellow-reds (oranges), instead of a wash of the same color, is a fair example. Any landscape image with lots of greens that are different when seen next to one another, but would be difficult to tell apart when seen separately, would be another good candidate for look to perceptual, if you have those greens out of gamut.

Brian A

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