Color Shifts depending on Location on a Page

[Doug Gray]

Interesting.. I think it causes by platen height changes too, paper warp or bending.

Epson desktop printers manual points this out. In P600 manual shows "Top/reduced print quality area: 1.30 inches (33 mm) minimum" and "Bottom/reduced print quality area: 1.42 inches (36 mm) minimum". The numbers are the same with P700/P900. Actually, there has the same info in Canon PRO1000's Manual (attached image below). But Canon has a wider quality reduced area, top 53.3 mm, bottom 49.5 mm. It's roughly 2" in length.

Larger printers have vacuum suction keeping papers on the plate to avoid this issue. P7000, P9000, P7500, P9500 did not have that statement in manual. But in my own experience, P9500 has similar issue on top of the paper.

Yep. Thanks for that. I never thought to look in the manual under specifications. I have 1.5" top and bottom margins. There's still some effects at 2" and have to go to 2.4" on the bottom and 2" on the top before the L* change drops below .3  That's not quite what the manual states but it's close.

So all this time people have been making profiles with significant portions of the printer area outside of the "good" zone. Wow.

As an experiment I also tried putting a gentle curve in the bottom of the paper in both directions. There was no difference and exactly the same effects occurred with both. So it isn't paper warp.

[mearussi]

Yep. Thanks for that. I never thought to look in the manual under specifications. I have 1.5" top and bottom margins. There's still some effects at 2" and have to go to 2.4" on the bottom and 2" on the top before the L* change drops below .3  That's not quite what the manual states but it's close.

So all this time people have been making profiles with significant portions of the printer area outside of the "good" zone. Wow.

As an experiment I also tried putting a gentle curve in the bottom of the paper in both directions. There was no difference and exactly the same effects occurred with both. So it isn't paper warp.

Now we know. When all else fails read the instructions.

[JRSmit]

Yep. Thanks for that. I never thought to look in the manual under specifications. I have 1.5" top and bottom margins. There's still some effects at 2" and have to go to 2.4" on the bottom and 2" on the top before the L* change drops below .3  That's not quite what the manual states but it's close.

So all this time people have been making profiles with significant portions of the printer area outside of the "good" zone. Wow.

As an experiment I also tried putting a gentle curve in the bottom of the paper in both directions. There was no difference and exactly the same effects occurred with both. So it isn't paper warp.

The double head printers of Epson, 75/95xx not excepted, all have a print quality issue at the beginning of a print. The driver has options to select how the printer should handle the first few inches (per edge quality).

[datro]

In my case, (7900, see my above post), the phenomenon occurs regardless of where on the page the target is positioned.  I don't believe it has anything to do with the "degraded print quality" that occurs in the 1" top and bottom margins of Epson printers.  I ran many tests to verify this.  So I am convinced that there is something else at play...and I lean towards something related to the ink delivery system up to and including the head.

[Doug Gray]

In my case, (7900, see my above post), the phenomenon occurs regardless of where on the page the target is positioned.  I don't believe it has anything to do with the "degraded print quality" that occurs in the 1" top and bottom margins of Epson printers.  I ran many tests to verify this.  So I am convinced that there is something else at play...and I lean towards something related to the ink delivery system up to and including the head.

With the Canon 9500II, there were significant history effects. That is the colors of adjacent patches impacted  those nearby. For instance I would see a deltaE change of 1.5 on a dark patch if surrounded by dark patches. This doesn't occur on the 9800 or Pro1000. And on the 9800 there wasn't sensitivity to patches being printed near the top or bottom of the page but there was sensitivity to where the patches were located horizontally. This turned out to be fixable by tweaking the vacuum setting.

[Doug Gray]

Holy cow. I took my optimized, 957 single page patch i1iSis chart which uses packed RGBs and 102 extra near neutrals and re-randomized it to place all the near neutrals away from the top/bottom edges so the most saturated colors are at the outer 10 rows. Then I measured all the device neutrals and the L* smoothness between steps improved from an rms value of .35 to .14. Since dE2000 is most sensitive near the neutral axis and drops in sensitivity by large amounts as colors become increasingly saturated, this suggests either profiles should be made with large margins (2.5") on top/bottom or patches should be arranged on the charts such that the most saturated colors are nearest the top/bottom.

This also explains why adding lots of near neutrals on large chart sets (>3k) made very small improvements in near neutral color accuracy. It may well be that the single page chart will now show better near neutral color accuracy than a 3k chart. That's next to investigate.

[MfAlab]

I did a personal test to figure out will this issue cause quality problem. A full letter size resolution test chart be made. CTF line pairs are between 20 to 800 dpi. Printed it, scanned it and analyzed it.

First attachment shows the image and analyzed area. Distance to the bottom edge of paper are 0.3 cm,  0.8 cm, 2.0 cm, 4.7 cm, 8.3 cm and 12.2 cm. I use ImageJ to analyze the contrast of the scanned file in these areas. Results are in second attachment. X axis is the position along CTF line pairs, Y axis is the gray value. The contrast in "image quality reduced area" is sightly lower. That means resolution near paper edge is lower than center of the paper.

It is tested on EPSON P600, would like to see any results on other printers.

[Doug Gray]

Oh my. Turns out the patch location profiling the Pro1000 has really large effects on profile quality.

I've already discussed the impact of always printing profile targets after an initial page and discarding that page. This is critical even if you have already printed a page recently (within the last few minutes). There is some sort of change that occurs when there is any delay between printing successive pages. Here's an example of how bad it is.

The following is dE(1976) from 180 random colors in the printer's gamut and colors from the neutral axis from L*=3 to 93 in steps of 1.

Printing a 957 patch i1iSis page after the prior page was printed 8 hours earlier.
dE 180 color patches: 1.910  dE of 91 neutral patches: 1.089

However, discarding the first page and printing the chart immediately again reduces improves the profile accuracy.
The second 957 patch i1iSis page immediately after the prior page.
dE 180 color patches: 1.187  dE of 91 neutral patches: 0.570

And it gets better. Printing the same 957 patches on two consecutive pages where the page length was limited to 23 rows of 29 patches (667 total) improved the profile accuracy yet again.
dE 180 color patches: 0.819  dE of 91 neutral patches: 0.456

Summary: For the Pro1000, charts should be printed so the there is 2.5" margin along the long side of a US letter size (11" x 8.5") paper and an initial, first page duplicate discarded.

Notes:
1. Applies only to the Pro1000. My Epson 9800 does not exhibit significant near edge variations nor first page differences unless days unprinted have occurred.
2. This is for glossy prints at highest settings. Matte prints tend to have about 30% smaller errors.
3. The effect is really quite large. To the point that better profiles are made with 600 patches than 2000 patches when the first page is discarded and the charts provide 2.5" margins top and bottom.

[aaron125]

Oh my. Turns out the patch location profiling the Pro1000 has really large effects on profile quality.

I've already discussed the impact of always printing profile targets after an initial page and discarding that page. This is critical even if you have already printed a page recently (within the last few minutes). There is some sort of change that occurs when there is any delay between printing successive pages. Here's an example of how bad it is.

The following is dE(1976) from 180 random colors in the printer's gamut and colors from the neutral axis from L*=3 to 93 in steps of 1.

Printing a 957 patch i1iSis page after the prior page was printed 8 hours earlier.
dE 180 color patches: 1.910  dE of 91 neutral patches: 1.089

However, discarding the first page and printing the chart immediately again reduces improves the profile accuracy.
The second 957 patch i1iSis page immediately after the prior page.
dE 180 color patches: 1.187  dE of 91 neutral patches: 0.570

And it gets better. Printing the same 957 patches on two consecutive pages where the page length was limited to 23 rows of 29 patches (667 total) improved the profile accuracy yet again.
dE 180 color patches: 0.819  dE of 91 neutral patches: 0.456

Summary: For the Pro1000, charts should be printed so the there is 2.5" margin along the long side of a US letter size (11" x 8.5") paper and an initial, first page duplicate discarded.

Notes:
1. Applies only to the Pro1000. My Epson 9800 does not exhibit significant near edge variations nor first page differences unless days unprinted have occurred.
2. This is for glossy prints at highest settings. Matte prints tend to have about 30% smaller errors.
3. The effect is really quite large. To the point that better profiles are made with 600 patches than 2000 patches when the first page is discarded and the charts provide 2.5" margins top and bottom.

Just wondering about the cheapest way to achieve the highest degree of accuracy (as I also have a Pro1000), what needs to be on the initial page which is discarded? As in, could the first page be just a few patches of each colour or perhaps some text, etc such that the wasted ink costs are minimised?

If not, does the entire chart have to be printed and discarded or would, perhaps, say 1/2 or 1/4 of the chart be sufficient to remove the variability?