accuracy of ink coverage

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Ian Craig
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Joined: 28 May 2009, 10:27

accuracy of ink coverage

Post by Ian Craig » 28 May 2009, 10:53

I am at present trying to evaluate the accuracy of the Toner/ink coverage results and have come accross what appears to be a serious deficiency. When I test 2 seperate pages 1 with a 5% of area box coloured in C100 Y100 M100 K100 and a second with 4 seperate 5% of area boxes each being 100% of iether CMYK (ie one box is C100 second box is M100 etc)(Just to clarify the pages are of identical sizes and the boxes are of identical sizes) Although I get identical results in the CMYK density (5.10%) for each colour, the equivalent (5% pages) result are completely different, in the case of the box with all colours present at 100% I get an equivalence of 1.06 (roughly about what should be expected) but in the case of the 4 seperate boxes I get an equivalence of 1.88 where I would have expected the result to be identical as both instances will use identical amounts of toner/ink, (this is easy to justify as in the case of a litho printed job each page will produce 4 plates with identical size boxes, the only difference being the position of the boxes on the plates which has no bearing on the coverage value) what is going wrong? as as it stands I could not trust the results from APFill to give me accurate enough results to calculate ink / toner costs I could be nearly twice the cost out in one direction or the other.

Regards

Ian

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Re: accuracy of ink coverage

Post by support » 28 May 2009, 11:15

Hello

Could you send these test documents to support@avpsoft.com

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Re: accuracy of ink coverage

Post by support » 29 May 2009, 12:24

I've tested this document.
Obviously you calculate this document for resolution <100 dpi. For resolutions >=100 you will get no difference in coverage.

APFill uses ghostscript to render PDF file to separated tiff files (here resolution is used) and then calculates coverage for these tiff files. If you set low resolution then rendering is fast but coverage calculation isn't accurate because of low tiff quality. If you set high resolution the rendering is slow but coverage calculation is accurate because of high tiff quality. So ususally to get accurate results and fast calculation - 150-300 dpi is enought.

If you use resolution <100 you get low quality tiff files and here figure place is important for example some figure edge pixels can be not pure black (blurred) because of place and low resolution.

Ian Craig
Posts: 4
Joined: 28 May 2009, 10:27

Re: accuracy of ink coverage

Post by Ian Craig » 01 Jun 2009, 15:23

I take your point about tiffs not being as acurate at lower resolutions but not to the extent of doubling the results, a small % difference only would be expected. Have tried re testing at differing resolutions all the way up to 600dpi which is the highest your application allows and the results are still incorrect. I should get identical results for both pages but the second page is coming out at twice the ink coverage as the first page, This is Wrong. I am not interested in any technical considerations about the use of Ghostscript all I require is the knowlege that your product works, which I am sorry to say it very clearly doesn't

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Re: accuracy of ink coverage

Post by support » 01 Jun 2009, 19:56

If you want to measure CMYK coverge you should use CMYK coverage mode ("CMYK coverage ratio (PS,PDF)" APFill menu item).
Here are results for your document for different resolution:

50 dpi:

Code: Select all

Page	C	M	Y	K	S1	S2	S3	S4	S5	S6	S7	S8
1	5,22	5,22	5,22	5,22	0,00	0,00	0,00	0,00	0,00	0,00	0,00	0,00
2	5,10	5,10	5,22	4,99	0,00	0,00	0,00	0,00	0,00	0,00	0,00	0,00
Average	5,16	5,16	5,22	5,11	0,00	0,00	0,00	0,00	0,00	0,00	0,00	0,00
150 dpi

Code: Select all

Page	C	M	Y	K	S1	S2	S3	S4	S5	S6	S7	S8
1	5,06	5,06	5,06	5,06	0,00	0,00	0,00	0,00	0,00	0,00	0,00	0,00
2	5,06	5,06	5,06	5,06	0,00	0,00	0,00	0,00	0,00	0,00	0,00	0,00
Average	5,06	5,06	5,06	5,06	0,00	0,00	0,00	0,00	0,00	0,00	0,00	0,00
So for 150 dpi we get equal results for both pages and even for 50 dpi maximum error is 0.30% .
Maybe you measure RGB coverage?

Ian Craig
Posts: 4
Joined: 28 May 2009, 10:27

Re: accuracy of ink coverage

Post by Ian Craig » 03 Jun 2009, 11:01

OK Try again

It is not the actual CMYK Density tab I am concerned about but rather the way "It is equivalent to (5% pages)" interprets the results, Try actualy looking at your own programme.

IT IS EQUIVALENT TO (5% PAGES): displays the number of standard 5% pages to which your layout sheet is equivalent. That is, when "Page total coverage density" equals 10%, this means the printer will use the amount of ink/toner sufficient to print two pages with the standard 5% coverage density.

IT IS EQUIVALENT TO (5% PAGES) = PAGE TOTAL COVERAGE DENSITY/5

It is NOT possible to to put down exactly the same amount of Ink / Toner on two differnt jobs that only vary in the position of the ink / toner, (not the quantity) and yet some how one of the jobs according to your results magicaly requires the equivalent of twice the amount of ink / toner, and since this is the part I am suppose to refer to in order to calculate ink / toner costs
it is clearly of now usable value whatsoever, unless I ignore your own insrtuctions and do all my calculations directly from the
cmyk density tab, which rather makes your "it is equivalent to (5% pages)" rather redundant and very misleading and potentialy extreamly costly

support
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Re: accuracy of ink coverage

Post by support » 03 Jun 2009, 16:10

CMYK coverage CAN'T be equivalent RGB coverage. So if you want to measure CMYK coverage please use "CMYK coverage" menu item.
If you use "CMYK+RGB" menu item all results except "CMYK" tab is RGB results (IT IS EQUIVALENT TO (5% PAGES) too).

Ian Craig
Posts: 4
Joined: 28 May 2009, 10:27

Re: accuracy of ink coverage

Post by Ian Craig » 04 Jun 2009, 11:05

IT IS EQUIVALENT TO (5% PAGES): displays the number of standard 5% pages to which your layout sheet is equivalent. That is, when "Page total coverage density" equals 10%, this means the printer will use the amount of ink/toner sufficient to print two pages with the standard 5% coverage density.

Please read your own manual statement above and then explain how this can only refer to RGB results as NO printer prints in RGB (This is a process of mixing light to achieve variable colours) physical full colour printers print in CMYK (or spot colours but that is not the issue) therefore the "it is equivalent to (5% pages) ONLY has meaning with reference to CMYK printing and therefore the cmyk results, at no point have I infered or claimed that RGB results and CMYK results should be the same or equivalent, I am questioning the validity of using the "it is equivalent" sumary to calculate toner usage. If it is not for this purpose what is it there for? If you cannot use it for calculating toner coverage and can only gain the correct information from the CMYK result table then please say so

Thank you

PS
is there any way of getting APFill to give results in only CMYK when there is spot colour information in the document (i.e. include spot colours in the cmyk instead of showing them as seperate inks, or do you have to convert spot colours to cmyk before running through APfill?

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Re: accuracy of ink coverage

Post by support » 04 Jun 2009, 20:16

Hello

Yes in CMYK+RGB mode "IT IS EQUIVALENT TO" is used for RGB only.

If you have additional spots in your PDF or PS document APFill can measure them (CMYK + 8 additional spots) you should use the "CMYK coverage ratio" menu item.

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