Author Topic: scanning resolution on flatbed scanner (Read 10697 times)

mtkang · « **on:** October 21, 2010, 09:08 »

Hi all,

I have some question about scanning on flatbed scanner, i am trying to scan some of my sketch on flatbed scanner.

I saw the highest resolution of my flatbed scanner is 1200dpi, so i scanned with this option and i got a 132mb TIFF, 14000x9900 pixels.

when i tried to re-size it in photoshop, i saw the resolution is 1200pixel per inch.

I am not sure what i do is correct, but i think it is usually 300 pixel per inch for printing, so i set it to 300 pixel/inch, the size of TIFF change to 3500x2500 pixels, and the files size is from 132MB to 8.3MB.

i am not sure what i am doing, but what setting i should do to preserve the quality? i thought that changing pixels/inch is only a way of calculation and not affecting the image quality, but why such a reduce in file size?

anyone can advise what i should do?

madelaide · « **Reply #1 on:** October 21, 2010, 13:49 »

I don't use PS, but I suppose there is a checkbox in which you set "no resize" or something like that. So you can change dpi without changing pixel size.

rimglow · « **Reply #2 on:** October 21, 2010, 14:17 »

When you open the Image Size dialogue box, uncheck the Resample Image box. Then make the Resolution change. That's the difference between Resizing and Resampling.

Here's the tutorial:
http://www.photoshopessentials.com/essentials/resizing-vs-resampling2.php

mtkang · « **Reply #3 on:** October 22, 2010, 02:58 »

thanks for the link, but i still not really understand what i should do.

It seems the pixels/inch is only affecting printing results? i am not sure i should resize of resample it.

anyone can tell me more what i should do for my scanned files?
132mb TIFF, 14000x9900 pixels, 1200 dpi..

is it a must to set jpg 300dpi?

Christos Georghiou · « **Reply #4 on:** October 22, 2010, 03:19 »

Hi mtkang
The actual pixel dimensions of the image dictate the "quality" (the number of little pixel squares that make up the image). The ppi (or dpi for printing) tells it how to display or print.
If want to just change how it displays or prints by default but keep the image fundamentally the same then you can Open the the Image Size dialogue box, put in the desired ppi then put in the original dimensions in the hight/width boxes, which will have changed with the ppi (do this without closing and reopening the box, or you will downsize then upsize with horrible results).
You will know if you do it right because PS wont have to make any calculations, the change will happen instantly and the image should look no different.

massman · « **Reply #5 on:** October 22, 2010, 04:27 »

This may help: http://www.scantips.com/calc.html

If not, post a specific question and I'll try and answer it for you. Google is pretty good at finding stuff

mtkang · « **Reply #6 on:** October 22, 2010, 05:15 »

i am not printing it at this moment, my purpose is to prepare a file to sell as a stock like in alamy.

i scanned as 1200 dpi, and this is the file i got
132mb TIFF, 14000x9900 pixels

i want to convert to jpg, i click photo 'image size' and there are pixels dimension and document size, i saw the document size is showed as 1200 pixels/inch

i am not sure what the setting i should get my jpg, do i have to change it to 300 pixels/ inch in the 'document size' setting? and i notice if i change to 300 pixels/inch the pixels dimension change to smaller sizes.

should i just ignore the pixels/inch and only adjust the pixels size to get a jpg size i need?

Blufish · « **Reply #7 on:** October 22, 2010, 07:34 »

Set the document size to 300 dpi. That should do it.

mtkang · « **Reply #8 on:** October 22, 2010, 07:45 »

when i set 300dpi, the whole images pixel size is becoming 3000x2000 something, does it mean I 'shrink' the image and didn't preserve the original quality?

Quote from: Blufish on October 22, 2010, 07:34

Set the document size to 300 dpi. That should do it.

Blufish · « **Reply #9 on:** October 22, 2010, 08:01 »

If you change the dpi you cannot keep the pixel size. If you do, then you will be resampling and it wont look good. Dpi and pixel size go hand in hand. If you want the image larger than the 3000x2000 you have to scan it at an even higher resolution.

massman · « **Reply #10 on:** October 22, 2010, 08:45 »

Quote from: mtkang on October 22, 2010, 05:15

i am not printing it at this moment, my purpose is to prepare a file to sell as a stock like in alamy.

i scanned as 1200 dpi, and this is the file i got
132mb TIFF, 14000x9900 pixels

i want to convert to jpg, i click photo 'image size' and there are pixels dimension and document size, i saw the document size is showed as 1200 pixels/inch

i am not sure what the setting i should get my jpg, do i have to change it to 300 pixels/ inch in the 'document size' setting? and i notice if i change to 300 pixels/inch the pixels dimension change to smaller sizes.

should i just ignore the pixels/inch and only adjust the pixels size to get a jpg size i need?

Okay, you have scanned a file at 14000 x 9900 pixels, this is what is important. For now, forget about file format, size and DPI. You have a bitmap image that is 14000 x 9900 pixels, you have created an image that is 138 mega-pixels, a huge file. What size file do you want to create?

Kone · « **Reply #11 on:** October 22, 2010, 08:46 »

Hi mtkang,
Here is another tutorial:
http://tv.adobe.com/watch/learn-photoshop-cs4/getting-started-09-resizing-an-image/

Ps:
Why did you at first time set your scaner to 1200 dpi ? This is only for printing.
Todays standard is 300 (360 dpi max)

madelaide · « **Reply #12 on:** October 22, 2010, 18:56 »

mtkang,

What are you scanning at 1200 dpi? A printed image? I remember HP saying it's useless to scan at above 600dpi because this is the maximum printing resolution for photo prints. Going beyond that is like using digital zoom. And even 600 dpi may be a higher resolution than the original print had.

Most sites don't require a specific dpi, but there is one (hmm, which one?) that requires 300dpi. But as Rimglow explained, you have to uncheck the "Resample Image" box, so you change dpi without changing image size in pixels.

mtkang · « **Reply #13 on:** October 23, 2010, 00:32 »

i am scanning a pen sketch on a sketchbook paper, the reason i scanned at 1200dpi, because when i use the software, i saw the highest choice of 'resolution' is 1200 dpi. I am just thinking to scan at highest resolution so that i can scan it one time and resize for multiple purpose.

Quote from: madelaide on October 22, 2010, 18:56

mtkang,

What are you scanning at 1200 dpi? A printed image? I remember HP saying it's useless to scan at above 600dpi because this is the maximum printing resolution for photo prints. Going beyond that is like using digital zoom. And even 600 dpi may be a higher resolution than the original print had.

Most sites don't require a specific dpi, but there is one (hmm, which one?) that requires 300dpi. But as Rimglow explained, you have to uncheck the "Resample Image" box, so you change dpi without changing image size in pixels.

mtkang · « **Reply #14 on:** October 23, 2010, 00:37 »

Quote from: massman on October 22, 2010, 08:45

Quote from: mtkang on October 22, 2010, 05:15
i am not printing it at this moment, my purpose is to prepare a file to sell as a stock like in alamy.

i scanned as 1200 dpi, and this is the file i got
132mb TIFF, 14000x9900 pixels

i want to convert to jpg, i click photo 'image size' and there are pixels dimension and document size, i saw the document size is showed as 1200 pixels/inch

i am not sure what the setting i should get my jpg, do i have to change it to 300 pixels/ inch in the 'document size' setting? and i notice if i change to 300 pixels/inch the pixels dimension change to smaller sizes.

should i just ignore the pixels/inch and only adjust the pixels size to get a jpg size i need?

Okay, you have scanned a file at 14000 x 9900 pixels, this is what is important. For now, forget about file format, size and DPI. You have a bitmap image that is 14000 x 9900 pixels, you have created an image that is 138 mega-pixels, a huge file. What size file do you want to create?

hi massman, i want a jpg format that's less than uncompressed size 100mb.

i also want to understand what is the way i should do in order not to change the image quality. Just like blufish said it, change to 300dpi? the pixels size will change in this case, any quality change of image?

madelaide · « **Reply #15 on:** October 23, 2010, 11:15 »

mtkang,

You don't need to use 300 dpi. As I said, there is one site, but I think it's not one of the micros, that require 300dpi. But regardless of dpi, what you have to check is if the image looks well at 100% zoom. If not, you may want to downsize it - again, regardless of the ppi/dpi.

Its like when we take a photo and it isn't quite sharp at its original size (say, 12MPix), so you downsize it to 8Mpix and it looks fine.

Also check your scanner's manual and see if 1200 dpi is its optical resolution. Some scanners offer a higher resolution than its sensor is able to achieve, and it is a software upsizing (say, 600dpi of the optical resolution upsized digitally to 1200dpi).

massman · « **Reply #16 on:** October 23, 2010, 14:52 »

Open your image and make your 'image size' dialog box the same as this one, start with the resolution and then the pixel dimensions. This screen grab is based on your image size of 14000 x 9900 down-sampled to create an uncompressed file of less than 100MB, you will suffer no loss of image quality. Save as jpeg. This will give you the solution you are after.

massman · « **Reply #17 on:** October 23, 2010, 15:09 »

If you compare this screen shot with the previous one you will notice that the pixel dimensions are the same even though the resolution has changed. Keeping it simple, as a photographer/illustrator the information that is important to you is 'Pixel Dimensions'.

Search google and do a bit of reading, resolution and scanning is too big a subject to write about here.

mtkang · « **Reply #18 on:** October 24, 2010, 07:46 »

ok thanks everyone for explanations..

I read something like 'resample' is like changing the pixels..

I by resample is 'ticked', when i change the resolution of document from 1200 to 300 pixels/inch the pixel dimension shrinks.

I tried to unclick the 'resample' and pixels/inch is not affecting the pixel dimension.

For my understanding the pixels/inch and document document size is just a figure that should not change the pixel information, and the end user can always change it.

I just tried to change the pixel dimension as what massman had suggested 7000x4950 to keep it under 100mb and unclicked resample and change the resolution information.

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Author Topic: scanning resolution on flatbed scanner (Read 10697 times)

mtkang

madelaide

rimglow

mtkang

Christos Georghiou

massman

mtkang

Blufish

mtkang

Blufish

massman

Kone

madelaide

mtkang

mtkang

madelaide

massman

massman

mtkang

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