why is A3 sent to printer have a gap top & Bottom. Puzzling.?

[nurgle]

Hi, A3 is supposed to be a ration of 1 to 1.414.. and is supposed to be 297 & 420 MM. But when I send images to my Epson Sure Color 5070 large format printer, there is a very tiny gap top& Bottom. see screen capture. WHY.

I know there is a marked border, and the printer needs that for it 'grippers'. it can print a full bleed by sizing up and over-printing.
but that is not my point.
I am using the epson printer driver. I am defin ing my image as an A3, with a ratio of 1 to 1.414... but I end up with this fractional gap. (but it does print every pixel of the image, if I expand I loose pixle of the original image)

i often re-crop an extra fraction, and fill that area using the stamp tool. but then it is no exactly 1 to 1.414...

and even if is use the epson printer driver to 'auto expand' and print over the edges, as it can do, I have to add extra edge border that the printer then prints to the ink overflow, and wastes ink.

(I have a hobby retirement money maker with Stand at 2 antique centres selling repro old time A3 posters. now have over 200,000+ in my image library. been digital retouching retouching for 20 years)

I cant find an epson forums to ask this on.

regards, Sandy

 

[thebestcpu]

Hi @nurgle
Yes I believe I can explain that small gap.
Note that once you scale your image, that gap is 1.5mm on top and bottom

Starting Size of Paper is not quite A3	296.7 mm	419.8 mm	See dimensions at top of print panel
Margin on all sides is 3.5mm or 7mm total	7 mm	7 mm
Frame size available for image	298.7 mm	412.8 mm
Multiplier of Height from width	1.4141
Calculated Height	409.7 mm	409.7mm
Total Gap in Height based on ratio. This is what happens when you use the Scale to Fit Media		3.1 mm
Total Gap in Height on each end divice by 2		1.55mm

So the gap is created by not starting exactly at A3 size,
followed by the margin being the same amount on all four sides
and calculating image height base on the A3 Height to Width ratio.

Hope this helps.
John Wheeler
BTW - all this does is create a 1.55 mm extra white gap on top and bottom (boundary lines are not there) so hardly visible in actual practice yet now I hope this satisfies your curiosity on why the gap shows up.

 

[nurgle]

when i made that document for the illustration purposes, I defined it as new document, international paper, A3. so it is an exact A3, according to photoshop.

as most people frame my A3 posters the gap disappears under the frame rebate, so is not seen. but I only posted my thing here as It has always puzzled me.

just one of those puzzling anomalies I keep on coming across.

but your explanation sounds logical.

Regards, Sandy

 

[thebestcpu]

HI @nurgle / Sandy
So instead of taking the measurements from the image you provided, I used the specifications for your printer shown in the image below. It indicates that the printable margin on all sides is 3mm



So using absolute numbers of paper size and the specified printer margins I come up with about the same result when the Scale to Media is used. I will use the table approach to go through what you are seeing.

Total A3 paper size in portrait	W= 297mm H=420 mm
Take off 3mm on all sides (6mm total width and height)	W= 291mm H=414mm
Keeping the A3 aspect ratio of 1.4141 What is the scaled height for the image	411.5 mm
Extra height relative to height margin	414mm - 411.5mm = 2.5mm
Extra space to 3mm marging divide by 2	2.5mm /2 = 1.25 mm

So assuming that the outside boundary represents the printable area when using Scale to fit media, the the inside boundary (gaps bottom and top of 1.25mm) would represent the actual print size when scaling an A3 image in portrait mode to 6 mm narrower and still maintaining the A3 aspect ratio.

So this approach using printer specs comes up with the same answer. Its just the difference between the potentially printable area (outer margin) and the actual printing area scaling to fit media in width and keeping the A3 aspect ratio for height.

Hope this provides a bit more clarity
John Wheeler

 

[nurgle]

hi, thanks again for a very professional answer.

(now more muddled and confuses as ever)but understand most of it.
(I was brought up on 10"x8" cameras)

but have been lecturing on photoshop photoshop 3. (not CS3) (but as for anything else to do under the hood of a computer I am lost)

but I must say, I greatly appreciate the amount of work and thorough explanation you have gone into. hence why this forum is important.

best wishes
Sandy Barrie.
Honorary Life Member, Australian Institute of Professional Photographers.

 

[thebestcpu]

Hi @nurgle / Sandy
I remember that picture from some post way back and still very impressive.

Sorry the explanation did not come through very well (that happens with my explanations not infrequently).
I will give it another angle that you can try and see if the gap goes away.

You noted that the aspect ratio that you are using is H/W of 1.414 or 420mm/297mm (A3 size) which is 1.414 (or actually 1.4141414 with more digits)
However, your printer steals 3mm on each side so the print area aspect ratio is 414mm/291mm which is 1.423 (or 1.4226804 for the same number of digits)

If you change the aspect ratio of your image (e.g. with the crop tool) to the later number then that little white space on top and bottom will disappear when using the print panel (I bet).
Again not necessary, all it does if you don't change the aspect ratio is leave a little white space on the top and bottom.
Never give up, never surrender (Galaxy Quest )
John Wheeler

 

[nurgle]

Hi, no your explanation came through VERY well an impressive. i am just an old dog and it was a trivial question answered in the top-level degree. clearly a master in your field.

Regards, Sandy