Resolution vs. Quality? suggestions? the norm?

GC
Posted By
George_C.
Mar 7, 2004
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673
Replies
4
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Closed
Just learning about photos, would like to know more about “resolution” and getting my digital photos to print good. Am using Photoshop 6, and a photo quality HP color printer. Have used Photoshop some…sort of a mid-level user. Here’s situation, would greatly appreciate your suggestions.

-Opened a jpg image (187kb), made with a digital camera. Just want to sure up colors, and also change the size of the picture.

-The image’s original specs were… Image > Image size > it’s Pixels=960×1280, Size=13x17approx, Res=72dpi

-I changed the image to Size=4×6, Res=1200, resample=bicubic. Prints good, although filesize huge (2.3MB). Questions are…

1. RES vs. QUALITY. When I saved it as jpg, Photoshop asks for a “quality”. I used “8”. Why does it (appear) to have TWO things that dictate resolution… the res=1200 and the quality=8. Which thing should I adjust to get to a resolution that will print well. What if I used Res=300 and quality=10… is that better or worse that the former. What should I save the NEW and improved version as (and not lose data)? Why’s file so big? Can I delete the unadjusted original?

2. DOES IT KEEP QUALITY. 2) After resampling, have I downgraded the picture, meaning if I re-keyed the original figures…would it return to nearly exactly as it was originally, or did it lose data in the first resampling that it can’t recover?

3. WHAT ARE GUIDELINES. What do most people do to find a balance between giant files size and high quality print resolution…for instance… is there a rule of thumb or chart somewhere that a certain picture size like 4×6 should be set to res=X and quality=Y?

Thanks

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Colin_Walls
Mar 7, 2004
George

There are about 20 different questions here. So, I am going to give a few [randomish] comments that may enable you to focus.

1) You have a low res digital camera, so don’t expect large prints. It’ll just about do a full-frame 6×4.

2) Users of Photoshop would regard files of 100Mb and up as being "huge". A few Mb is tiny.

3) Resampling [upwards] is generally bad and should only be done when you have no choice.

4) Don’t save as a JPEG unless you are posting on the Web and then just save a copy. JPEGs are compressed – that’s why cameras use this format. Compression doesn’t come free. Every time you decompress [open] and recompress [save] a JPEG, you are damaging the image quality. So, when you work on an image, save it as a PSD. Bigger, but lossless.

5) You need an image resolution of around 200ppi or higher [300ppi is nice] to get a good print.

Is this helping?
SW
Stormy Weather
Mar 7, 2004
for inkjets I have always preferred 600DPI, for my color laser at home it’s a lower 300 DPI, and for a large-format printer, I generally use 300DPI, but that’s only what I OUTPUT to, usually in PDF with JPEG and high quality. I keep all original files at least 600, usually 1200 DPI, and intact with layers, 250MB is not inordinately large. For practicality’s sake, any files I create for PS (Render from a 3D app,) I try not to render larger than 2560X2048 and normally just 1280X1024. I have had files as large as 1.12 GB and have 140 GB reserved for my documents folder.

wrote in message
Just learning about photos, would like to know more about "resolution" and
getting my digital photos to print good. Am using Photoshop 6, and a photo quality HP color printer. Have used Photoshop some.sort of a mid-level user. Here’s situation, would greatly appreciate your suggestions.
-Opened a jpg image (187kb), made with a digital camera. Just want to sure
up colors, and also change the size of the picture.
-The image’s original specs were. Image > Image size > it’s
Pixels=960×1280, Size=13x17approx, Res=72dpi
-I changed the image to Size=4×6, Res=1200, resample=bicubic. Prints good,
although filesize huge (2.3MB). Questions are.
1. RES vs. QUALITY. When I saved it as jpg, Photoshop asks for a
"quality". I used "8". Why does it (appear) to have TWO things that dictate resolution. the res=1200 and the quality=8. Which thing should I adjust to get to a resolution that will print well. What if I used Res=300 and quality=10. is that better or worse that the former. What should I save the NEW and improved version as (and not lose data)? Why’s file so big? Can I delete the unadjusted original?
2. DOES IT KEEP QUALITY. 2) After resampling, have I downgraded the
picture, meaning if I re-keyed the original figures.would it return to nearly exactly as it was originally, or did it lose data in the first resampling that it can’t recover?
3. WHAT ARE GUIDELINES. What do most people do to find a balance between
giant files size and high quality print resolution.for instance. is there a rule of thumb or chart somewhere that a certain picture size like 4×6 should be set to res=X and quality=Y?
Thanks
L
LenHewitt
Mar 7, 2004
George,

You certainly DO NOT need 1200 ppi to print to that printer. You are unlikely to see any improvement with anything over 240ppi and certainly no improvement whatsoever with anything over 300ppi.

Upsampling ALWAYS degrades the image. Noticeably. The more you upsample the more noticeable it will be.

Saving as JPEG degrades quality. The JPEG compression algorithm is ‘lossy’ and data is discarded. Re-saving a jpg as jpg results in even more image degradation.
CW
Colin_Walls
Mar 7, 2004
Ah, I see an issue:

You were after getting a 1200ppi image. Is that because you have a printer that does 1200dpi? PPI and DPI and not the same thing. This is a very common area for confusion.

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