Qimage "Auto" Rendering Intent (issue)

[jrsack]

Mike,

I love the Auto option when soft proofing.   I print images for others (non-commercial) and they say I do better than the commercial printers do -- and I explain it is because of Qimage.
I run every image I print through QU soft proof, note the rendering intent chosen by Qimage, and then go to the Mac version and plug that RI in.    Usually works beautifully.   

But I've had two images in two months where Auto chose Relative Colorimetric, and it should have been Perceptual.   

Do you know of cases where the Auto algorithm makes assumptions that might not be right?
The images have deeply saturated dark colors; but the Gamut warning does not show them as being out of gamut.
I am printing to a profiled paper (Canon Polypropylene Matte) and normally it works superbly. 

I can upload the images if you'd like.   I can even take pictures of the difference between RC and Perceptual when printed.   The difference is subtle, but these are very subtle images sometimes.

[admin]

If you've only run into two images in two months, that's probably as good as you can hope for as when you would choose RC over P is going to be subjective... as is the algorithm.  It is based on how much of the image is out of gamut and where the out of gamut areas occur.  More weight is given to the center for example so it would allow more out of gamut near the edges than it will allow in the center.  It's also a tradeoff between losing a little in out of gamut areas with RC versus desaturating the entire image (even in gamut colors) with P so that's a subjective threshold as well.

I will say that if nothing shows out of gamut, then nothing is really out of gamut BUT the new LCMS 2.17 color management engine does fix/improve the out of gamut warnings and that will be in QU 2025.102 which is in the very final stages of testing and I hope to get out tomorrow.  So be sure to retest when that is out.

P.S. To be honest, I just use RC all the time unless I see a specific problem with colors and that usually only happens with images that are filled with bright saturated colors.  With RC at least you know if the color can be rendered by your printer (it is not out of gamut) it will be rendered accurately.  With perceptual, literally nothing is rendered accurately: even the in gamut colors that could be printed correctly are shifted.  It fools our eyes because it's a relative shift of the whole image but I just like knowing that my printer rendered everything it can render accurately and I don't mind out of gamut colors being a little clipped.  That's usually less objectionable than desaturating the whole image a little like perceptual does.  That's pretty much how the auto intent works: it won't "give up" on RC unless there's quite a bit out of gamut that might produce objectionable banding or clipping when using RC with out of gamut colors.

Regards,
Mike

[jrsack]

I will watch for .102!

Thanks for this explanation of how Auto makes a judgement call.

One of the two images definitely fits "bright saturated colors":   the image has women at an Indian vegetable street market, and they are wearing gorgeous sarees, with some deep hues (think purple that looks black) that were not in the center of the image but on the periphery.   The sarees were the point of the image, but all around the circle, not in the center.

The other image is just a puzzlement to me.  The image is of an skyscraper with an unusal twisted design in bright sunlight, so it glows in different angles on the screen.  But it doesn't have that glow on the print.   A little better in perceptual but still not like the illuminated-from-behind screen.   I can't make it look right.    There are other smaller shadowed darker (brick) apartment buildings around, and those just look dull in RC, while perceptual brings them up a bit in luminosity.    The nice thing about this image is that the colors shifting a bit from RC to P isn't a big deal.

I run every image through Auto soft proof to see if it tells me Perceptual.   Rarely it says P (1 in 20?) but it does happen.

Anyway, thank you again for the exp, and for Qimage.   I have  a hundred photographers who swear I get better results than the professional printing houses (and I've seen the work from those shops and the photogs are right), and I tell them it is one program I depend on!