Qimage and RIPS

[Ed Richards]

I find sharpening for different print sizes the most maddening part of digital work. Qimage does a wonderful job of sharpening prints based on the target print size, as well as rerezing them for the optimal size for the printer. I am curious whether these files could then be saved to disk, rather than being sent directly to the printer, and then be printed through a RIP (imageprint) to optimize the color and control of the printer.

[Ted Harris]

Ed, sharpening should be a relatively straightforward procedure although, yes, you need to do it separately for each image size, just as you need to check critical focus separately for each new print size you are making in the wet darkroom. Careful, critical digital work is not necessarily faster or easier than wet darkroom work, in fact it sometimes takes even longer .... to me the major difference is you do one standing up in the dark and the other sitting down in the light. A good rule-of-thumb for sharpening your images is:

1) using unsharp masking set your radius to .5% of your resolution (.005 x resolution)

2) set your threshold between 0 and 5 depending on the image .... can’t give all the detail in a post but you will want a smaller threshold for landscapes and a larger one for portraits .. this is the separation between pixels.

3) start with an amount of 220% and back-off from there until you have the minimum acceptable sharpening amount (frequently you will end up at less than 100% with LF negatives and transparencies).

These are just guidelines but should work well with all images and, of course, you will need to watch your screen closely to see what the image looks like. Remember that if your screen image is not a size that is divisible by 2 (e.g. 50%/25%/12.5%) you will NOT get a good idea of the sharpening process.

The specifications for Qimage lead me to believe that it is performing some ‘tricks’ as part of its processing that I would not want in a master image and that likely will not give me final output that will equal my individual processing of an image ... sort of like a machine enlargement v. a totally controlled hand enlargement. I have not used the software sine we have a 100% Mac shop and it makes little sense to run imaging software through Virtual PC.

As with everything else, there are no magic bullets when preparing a digital print. The beauty (or horror in some folks' minds) of the process is that you CAN exactly replicate the procedure once you have the final print tht you like.

[Ed Richards]

Ted,

I do understand sharpening, I just said it was a pain.:-) Qimage is not that it is all I use - I also use selective sharpening on the master image. I just do not like to have to do a second custom sharping to resize the print. I have been very impressed with what Qimage can do, and it does not change the master image, it is a post-processor for printing. The combination of the resizing and smart sharpening is very effective, partially because it does not leave anything to the print driver. It is very useful when I am tuning an image and want to run multiple prints in smaller sizes to get the print the way I want it. I then reprint it in larger sizes without having to resharpen and run a new set of test prints. (I think the best way to see a print is to print it - just like the darkroom.)

[Antonio Corcuera]

"1) using unsharp masking set your radius to .5% of your resolution (.005 x resolution)"

Ted,
Does this mean .5% of output resolution?
(I normally USM at 180-200%, 0.3 radius, threshold 0-5, independent of print size)
Thanks!

[David Luttmann]

I've never been a fan of Qimage and have always considered it a waste of money. My biggest issue with it is the painterly effect that is quite often visible compared to a Photoshop Bicubic Smoother routine. Attached is a sample showing a large interpolated image from a 6MP sensor. Qimage is on the left, Photoshop Bicubic Smoother on the right. It's plainly evident that Qimage fails miserably. I thus put little faith in it's smart sharpening as well.

http://members.shaw.ca/daveandclaire/stuff/compare.jpg

[Ed Richards]

Dave,

I am working with 170 meg B&W files from 4x5. The issues are very different when you are down sampling files to print than upsampling them to try to fill in missing info.

[David Luttmann]

Ed,

Bad image interpolation is bad irrespective of file size. I used the above sample as a worst case test. However, it is obious that PS works better than Qimage does for interpolation.....even if it is less visible due to the file sizes you are dealing with. In the end, stick with PS for the highest quality output. Qimage is good only for those looking for shortcuts first, and image quality second.

[Ted Harris]

Antonio, yes, output resolution .... you shoiuld see some big differences when you change the radius based on the resolution. Leaving it at 0.3 is great for images you are going to show on the web but will gie you far from optimal results for printing .... of course, if you arae working with 8x10 or larger and/or a scan at 4000 ppior more from a drum scanner then such a small amount of sharpening is required that it is not worth discussing

[Jeremy_D]

QImage can be set to send its output to a file rather than a printer, so yes you can save the output of QImage to send to a RIP.

Mind you Qimage can handle ICC profiles just fine and you may not even need a RIP to control the printer.

[Ed Richards]

> Mind you Qimage can handle ICC profiles just fine and you may not even need a RIP to control the printer.

That is what I am hoping.