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FORUMS Post Processing, Marketing & Presenting Photos RAW, Post Processing & Printing 
Thread started 26 Feb 2018 (Monday) 08:21
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davesrose
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Feb 27, 2018 12:59 |  #91

Wilt wrote in post #18573691 (external link)
Similary, when we send a photo to our Canon or Epson, there is ZERO correlation of an embedded dpi value (if the EXIF is present) with how many dots of ink per inch are emitted by the printer.

Well for printing, PPI of image does come into play. As my link's example shows with the same pixel dimension of an image of a kitty: it can fill the printed paper at 72DPI and be smaller then a postage stamp at 1000 DPI. If the printer could print a true 1000 perceptual DPI, then that kitty would look good with a magnifying glass! The old standard of printing was that an image that had a native density of 300DPI was good for viewing at close distances. You could go down to 150DPI if it was for posters (where viewing distance wasn't as close), and then you can have a really small DPI for billboards. Now current photo printers have non-rectangular dot patterns, but usually are processing at 600 PPI. If you're printing for the greatest quality at very close viewing distance, then it's best to have a source resolution that can fill your intended dimension with native PPI. If the PPI is lower, the printer is doing its own re-sampling. You may or may not find a better re-sampling algorithm with Photoshop.


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Feb 27, 2018 13:24 |  #92

TeamSpeed wrote in post #18572977 (external link)
A 3600x2400 where section is cut out that is now 1800x1200 isn't a 50% crop, you have 1/4th the total image, not 1/2 the total image. If you take roughly 71% of the width and 71% of the height (if you want to keep the same aspect ratio), then the final 50% crop out of the image would give you a 2550 x 1700 final result.

Since a crop factor is a product of height and width, you need the square root.

Best thing is to specify which ratio (linear or area) is meant, because it could be either one.

In fact, my two resize tools (in PhotoLine and FS Image Viewer) both refer to linear ratios, not area.Therefore, if I set them to resize to 50%, I'll get 1/2 the pixels per each side, i.e. 1/4 total pixels.




  
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Wilt
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Post edited 6 months ago by Wilt. (2 edits in all)
     
Feb 27, 2018 13:30 as a reply to  @ davesrose's post |  #93

TeamSpeed wrote:
If you disagree, then take the image I posted where I did this and tell me why that doesn't work? Take my image and measure the area of the yellow box to that of the red box, and see if you come up with the same 72.8%. Where did this 17.2% discrepancy come from? (hint, the 2 image files posted were resized down by different amounts/aspects, playing havoc with your base assumptions).

To decrease measurement error, I had Windows display things on my monitor at 200% . I measured inside the colored boxes, due to the thinknesses of the box lines.
Red box interior dimensions, 380mm x 354mm, aspect ratio =1.07:1, area = 134520 sq.mm
Yellow box interior dimensions, 121mm x 80mm, aspect ratio = 1.51:1, area = 9680 sq.mm

Number crunching


  1. Horizontal linear reduction = 68.15% (259/380)
  2. Vertical linear reduction = 77.4% (274/354)
  3. Horizontal linear remaining = 31.8% (121/380)
  4. Vertical linear remaining = 22.6% (80/354)
  5. Area reduction = 92.8% (124840/134520)
  6. Area remaining = 7.2%


I don't see anything close to your 72.8% number. You can look at the source values above in each computation. Where is the great mismatch occurring? You gave your answer, but provided none of the input values for that computation.

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Wilt
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Feb 27, 2018 13:43 |  #94

davesrose wrote in post #18573710 (external link)
Well for printing, PPI of image does come into play. As my link's example shows with the same pixel dimension of an image of a kitty: it can fill the printed paper at 72DPI and be smaller then a postage stamp at 1000 DPI. If the printer could print a true 1000 perceptual DPI, then that kitty would look good with a magnifying glass! The old standard of printing was that an image that had a native density of 300DPI was good for viewing at close distances. You could go down to 150DPI if it was for posters (where viewing distance wasn't as close), and then you can have a really small DPI for billboards. Now current photo printers have non-rectangular dot patterns, but usually are processing at 600 PPI. If you're printing for the greatest quality at very close viewing distance, then it's best to have a source resolution that can fill your intended dimension with native PPI. If the PPI is lower, the printer is doing its own re-sampling. You may or may not find a better re-sampling algorithm with Photoshop.

Dave,
if you send me a 800x1000 JPG with 72 dpi in the EXIF, and I print it on my printer and specify 4x6" paper print borderless, I get 200 pixels per inch, and at 8.5 x 11" paper borderless I get 94 pixels per inch.
if you send me a 800x1000 JPG with 300 dpi in the EXIF, and I print it on my printer and specify 4x6" paper print borderless, I get 200 pixels per inch, and at 8.5 x 11" paper borderless I get 94 pixels per inch.
Same result comes from both because the embedded EXIF 'dpi' value means squat in the output to my printer.
If -- in my print driver -- I specify 'High' quality (vs. 'Standard' quality), both the '75 dpi' EXIF image and the '300 dpi' EXIF image will be formed with more dots of ink by my printer,
but with 'Standard' quality the output of both '72 dpi' EXIF image and '300 dpi' EXIF image will be formed with fewer dots of ink by my printer.


If you send those same two files to an offset printer, one print will look like sh*t (the one at 72 dpi) and resemble newsprint, while the other one will resemble National Geographic (300 dpi)


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davesrose
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Feb 27, 2018 14:07 as a reply to  @ Wilt's post |  #95

Wilt,

It doesn't seem like you're taking image resolution into account with printers. 72 DPI will resemble newsprint from any printer: whether it's from your home printer or you send it out. I was implying that with printing, DPI comes into play from your image dimension vs printed dimension. If you go to Photoshop and try resizing an image from 72DPI to a higher DPI, you will see that it has presets for 150DPI and 300DPI printed formats. By default, those images are saved at larger pixel dimensions (a 300 DPI image will take up twice as much filesize). With re-sampling, I was referring to using your image in Photoshop and making sure the intended print DPI fits your image resolution.

If I were printing a 8x6 page, my image would be 576x432 at 72DPI. If I wanted to make a jpeg that's 300DPI, the saved resolution is 2400x1800. With the example of the kitty having the same resolution, pixel dimensions cover more area at 72 DPI then 300 then 1000 (but then with larger dots and less sharpness).


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Feb 27, 2018 14:26 |  #96

Would a mod please rename this thread:

"what is the airspeed velocity of an unladen swallow?"

TIA


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Post edited 6 months ago by Wilt. (4 edits in all)
     
Feb 27, 2018 14:34 |  #97

davesrose wrote in post #18573767 (external link)
Wilt,

It doesn't seem like you're taking image resolution into account with printers. 72 DPI will resemble newsprint from any printer: whether it's from your home printer or you send it out. I was implying that with printing,

Ah, I see once again the great mixup of PIXELS per inch .vs 'DOTS' per inch (dpi). The prescribed DPI value has NO influence at all on the quality I get out of my Canon all-in-one printer. Not merely a theoretical statement, I have done it for real proof.
Earlier I said I know that if I printed the 800 x 1000 image at 4x6" I end up with 200 PIXELS per inch of print, and the same image at 8.5" x11" I have on 94 PIXELS per inch of print. The PPI is a net result, not a controlling parameter.

davesrose wrote:
DPI comes into play from your image dimension vs printed dimension.
If you go to Photoshop and try resizing an image from 72DPI to a higher DPI, you will see that it has presets for 150DPI and 300DPI printed formats. By default, those images are saved at larger pixel dimensions (a 300 DPI image will take up twice as much filesize). With re-sampling, I was referring to using your image in Photoshop and making sure the intended print DPI fits your image resolution.


If I were printing a 8x6 page, my image would be 576x432 at 72DPI. If I wanted to make a jpeg that's 300DPI, the saved resolution is 2400x1800. With the example of the kitty having the same resolution, pixel dimensions cover more area at 72 DPI then 300 then 1000 (but then with larger dots and less sharpness).

And that is because your application (my Lightroom does the same!) knows you want 8" wide print with 280 dpi so it recomputes the original image (from whichever camera) and outputs a file with resolution of 8*280, or 2240 pixels in that dimension. The app is resizing its ouput according to the print dimensions and the pixel-per-inch output you need. You might have only a Canon 50D with 4752x3168 pixels and want to have a 20x30" print made for you, and they 'require 300 dpi' so Photoshop resamples your original RAW file to output a 6000 x 9000 pixel JPG image that you can send to them.


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Feb 27, 2018 14:38 as a reply to  @ Left Handed Brisket's post |  #98

.


Ni !


.


"Your" and "you're" are different words with completely different meanings - please use the correct one.
"They're", "their", and "there" are different words with completely different meanings - please use the correct one.
"Fare" and "fair" are different words with completely different meanings - please use the correct one. The proper expression is "moot point", NOT "mute point".

  
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davesrose
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Feb 27, 2018 14:57 |  #99

Wilt wrote in post #18573782 (external link)
Ah, I see once again the great mixup of PIXELS per inch .vs 'DOTS' per inch (dpi)
I know that if I printed the 800 x 1000 image at 4x6" I end up with 200 PIXELS per inch of print, and the same image at 8.5" x11" I have on 94 PIXELS per inch of print

I think what confuses things is PPI for print vs PPI on screen. PPI on screen is solely you screen's resolution vs screen size. You'll see "96 dpi" is listed as resolution under properties of a jpeg (that is the default EXIF jpeg for Windows). If you'll see my above posts, I have been using PPI in regards to image and DPI in regards to printer density. When you're designing for screen, most times you're just regarding pixels (though for illustration, I'll make my document 300 DPI for having more control with paint brushes and having better print quality). Also, if you look at the discussions below that article I linked on web image DPI, you'll see front end developers and designers continue to complain that they get clients wanting both optimized web images that are also 300 DPI for print (which is meaningless without knowing output dimensions).

Wilt wrote in post #18573782 (external link)
You might have only a Canon 50D with 4752x3168 pixels and want to have a 20x30" print made for you, and they 'require 300 dpi' so Photoshop resamples your original RAW file to output a 6000 x 9000 pixel image that you can send to them.

Yeah, hence my previous statement about seeing if Photoshop has a better algorithm for re-sampling vs your printer:-)


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Feb 27, 2018 15:06 |  #100

Tom Reichner wrote in post #18573784 (external link)
.


Ni !


.


Nu !


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Feb 27, 2018 15:19 |  #101

I'll fetch the herring!


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Feb 27, 2018 15:20 |  #102

Dave,
Re-reading our last few message exchanges, it seems that we are each arguing from a different point of view.

  • Your example of presets in Photoshop of for 150DPI and 300DPI is precisely what had describe was used by the app (Photoshop or LR) in calculating the necessary pixel count, in order to CREATE an output file which would be a certain size with a certain dpi value in the output.
  • I, OTOH, am stating that if you have a JPG file in your possession, and send it to the Epson or Canon printer, NOTHING will change the quality of the output except for the printer driver Quality setting (High, Standard, Draft)...two files of identical content except for dpi value in EXIF will nevertheless print with identical quality.


both are correct, but they describe two different circumstances!

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Post edited 6 months ago by TeamSpeed. (2 edits in all)
     
Feb 27, 2018 15:33 |  #103

Wilt wrote in post #18573740 (external link)
To decrease measurement error, I had Windows display things on my monitor at 200% . I measured inside the colored boxes, due to the thinknesses of the box lines.
Red box interior dimensions, 380mm x 354mm, aspect ratio =1.07:1, area = 134520 sq.mm
Yellow box interior dimensions, 121mm x 80mm, aspect ratio = 1.51:1, area = 9680 sq.mm

Number crunching


  1. Horizontal linear reduction = 68.15% (259/380)
  2. Vertical linear reduction = 77.4% (274/354)
  3. Horizontal linear remaining = 31.8% (121/380)
  4. Vertical linear remaining = 22.6% (80/354)
  5. Area reduction = 92.8% (124840/134520)
  6. Area remaining = 7.2%


I don't see anything close to your 72.8% number. You can look at the source values above in each computation. Where is the great mismatch occurring? You gave your answer, but provided none of the input values for that computation.

I took the 72.8% that you quoted, but that was just for the horizontal, and I read that as being what was cropped away.

Mine is quite simple, I used just one image so that this error in different resizing ratios between the two posted images no longer apply. The % of image content thrown out is ( 1 - (area of yellow box / area of red box) ). The only error is in the bounding box for the yellow section where I may have not quite picked up enough of the scene or too much. This is simpler and more accurate because we don't need to know anything about the 2nd cropped image posted, other than what it looks like as taken from the original image.


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Feb 27, 2018 15:36 |  #104

What are you going to do, bleed on me? :D

Oh the memories...


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Feb 27, 2018 15:53 |  #105

TeamSpeed wrote in post #18573825 (external link)
I took the 72.8% that you quoted, but that was just for the horizontal, and I read that as being what was cropped away.

Huh? Are you saying that your 72.8% value represents the amount of horizontal image which was cut off?


So that would be directly comparable to my 1. Horizontal linear reduction = 68.15% (259/380)


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