Thread: Question on image format and social media

Originally Posted by xpatUSA

the degree of misinformation on the web is quite staggering!

Who would have thought that?

Unfortunately printer (and scanner) manufacturers are very unclear as to terminology and 9600 dpi sounds so much better than 300 dpi, even though 300 dpi is for all intents and purposes enough to be at the limit of what the human visual system can resolve. If I remember correctly a standard A4 / 8" x 10" print at arms length (~2x the print diagonal) printed at 270 dpi works.

There are four main variables that determine resolution and colour gamut in a print:

1. The number of inks that the printer uses; 8 inks is pretty standard for an entry level professional level photo printer. The number of inks drives gamut, more than resolution. Up to 12 different inks are used in the higher end models.

2. Droplets / Dot size - The printer can either deposit a droplet of ink (in the order of 4 picolitres per drop) or not. Some of the higher end printers have variable droplet size as well. Some produce droplets of 2 different sizes and some three different droplet sizes. A dot is determined by the number of inks + the number of droplets used per colour. As stated before, when it comes to inkjet printers, only Canon, Epson and HP make photo printers. Canon and Epson make a wide range of photo printers and HP only makes them in wide carriage printers (24" and wider). Canon and HP use a thermal print head design and have a native resolution of 300dpi. Epson uses and ultrasonic print head design and has a native resolution of 360 dpi.

3. Pigment vs dye based inks - most photo quality printers use pigment based inks, which use finely ground up minerals to produce the colours. These inks are mechanically attached to the surface of the paper. These inks are more resistant to colour change and fading over the life of the print. Dye based inks are absorbed by the paper fibres and can be more vibrant than pigment based inks. They tend to break down more quickly when exposed to UV and chemical agents in the air.

4. Paper - the medium that is being printed on has different optical properties that impact what the printed image looks like. The medium used is not always paper but can be a resin or metal. Most paper is not white, but the compounds it is coated with will affect the appearance of the final print. A matte paper tends to absorb the ink more and scatters light versus a luster of glossy paper. Matte papers tend to have a lower gamut than glossier ones. Print life is often impacted by the paper that is used; cotton rag tends to have the longest life, as long as it is acid free. Cellulose (wood fiber) based papers are often buffered to reduce the acidity in the paper to give longer print life. The paper manufacturers are generally not all that forthcoming with how their papers and coatings are formulated (unfortunately).

Originally Posted by Manfred M

Unfortunately printer (and scanner) manufacturers are very unclear as to terminology and 9600 dpi sounds so much better than 300 dpi, even though 300 dpi is for all intents and purposes enough to be at the limit of what the human visual system can resolve ...

... at about 12in distance, according to Snellen's 20/20 vision (6/6 in Canuckistan) i.e. one minute of arc. Many humans can do better than that, up to 24in away for 300 dpi.

If I remember correctly a standard A4 / 8" x 10" print at arms length (~2x the print diagonal) printed at 270 dpi works.

So 2x the print diagonal is about 26in. Works out to half a minute of arc, just distinguishable by the aforesaid many humans.

Interestingly, for DOF based on human vision, the 8x10in is held 10in from the nose ... about 360dpi using Snellen's criterion ...

Originally Posted by xpatUSA

Works out to half a minute of arc, just distinguishable by the aforesaid many humans.

Which suggests that the 300 dpi for Canon and HP should be just about indistinguishable for most folks and the 360 dpi that Epson uses is quite conservative and well beyond what humans can distinguish. A matte cotton rag paper has just enough scattering to make this a mute point, but someone with good eyes with a baryta (luster) finish paper might just be able to resolve the dots at 300 dpi.

Originally Posted by Manfred M

Originally Posted by xpatUSA Works out to half a minute of arc, just distinguishable by the aforesaid many humans.

Which suggests that the 300 dpi for Canon and HP should be just about indistinguishable for most folks and the 360 dpi that Epson uses is quite conservative and well beyond what humans can distinguish. A matte cotton rag paper has just enough scattering to make this a [moot] point, but someone with good eyes with a baryta (luster) finish paper might just be able to resolve the dots at 300 dpi.

At what distance, Manfred? Human visual acuity is based on angular measure, hence my minutes of arc.

In a perfect world (lighting, surface, contrast), someone with really good eyes could just distinguish 300dpi at 23in.

Originally Posted by Manfred M

Which suggests that the 300 dpi for Canon and HP should be just about indistinguishable for most folks and the 360 dpi that Epson uses is quite conservative and well beyond what humans can distinguish. A matte cotton rag paper has just enough scattering to make this a mute point, but someone with good eyes with a baryta (luster) finish paper might just be able to resolve the dots at 300 dpi.

An interesting question. I read review after review while deciding between the Epson P800 and the Canon Prograf 1000, and the number of people who mentioned perceiving a difference in detail was exactly zero.

Found this just now:

Printer Model Canon i9900 (plus 5 spares) I had a chance to look at some printed images under a good microscope, and I thought that others might also be interested. This image shows the ink "dots" printed for a thin, light band (a section of chain-link fence in the distance). It was necessary to select a light area, since the individual color dots could not be seen when a darker section was selected. Note the seemingly random pattern of the dots used to break up any repeating pattern that our eyes might pick up.

The full width of this image is about 700 microns (0.03"), and the "dots" are in the range of 50-70 microns (2-3 mils) in diameter. Note that the yellow dots appear to be slightly larger that the PM and PC dots. This illustrates that the colors that we see depend not only on how the inks color the paper, but also on how wide the ink spreads when it hits the paper. These dots were generated on a 2 pl printer, and a 1 pl printer should produce about 30% smaller dots (assuming that the ink is absorbed to the same depth for both dots).

please go to the link below to see the image.

Source: https://www.printerknowledge.com/thr...-on-paper.366/

The numbers are interesting ...

Originally Posted by xpatUSA

At what distance, Manfred? Human visual acuity is based on angular measure, hence my minutes of arc.

In a perfect world (lighting, surface, contrast), someone with really good eyes could just distinguish 300dpi at 23in.

8x10 print at 25" as per my earlier comment.

Originally Posted by Manfred M

8x10 print at 25" as per my earlier comment.

Thank you.

Found a new-to-me metric: npi = print-head nozzles per inch.

https://www.xaar.com/media/1303/prin...hite-paper.pdf


Do scroll down to the heading Viewing Distance ...

Resolving power decreases with an increase in distance so that at the average reading distance of 30 cm (12"), the finest resolution that the eye (at one arc minute) can perceive under ideal viewing conditions is 89 microns or about 300 dpi.

Back to Snellen, eh?

Originally Posted by xpatUSA

Thank you.

Found a new-to-me metric: npi = print-head nozzles per inch.

https://www.xaar.com/media/1303/prin...hite-paper.pdf


Do scroll down to the heading Viewing Distance ...



Back to Snellen, eh?

An interesting read. Xaar, like Epson uses piezoelectric technology in their print heads. Epson is part of the Seiko Epson Corporation and my understanding is that the print head technology that they use is an offshoot of the ultrasonic technology used in Seiko watches. Cavitation is used to propel the ink onto the print medium.

Canon and HP use heat that effectively boils the water in the inks to propel the ink onto the print medium.

I wonder who uses Xaar print heads, as Epson seems to build their own.

https://global.epson.com/innovation/...cro_piezo.html

Originally Posted by xpatUSA

Welcome!

What are those nuances, please?

I hope his reply is not too "nuanced".

I'm sorry, maybe my question will be off-topic, but could you give me a couple of tips on the development of Instagram? For example, there are scientific blogs where they tell exciting things. I even decided to create a similar blog, where I planned to talk about various historical events. However, I just started this blog, and I had few subscribers.

Originally Posted by Maplepsan

I'm sorry, maybe my question will be off-topic, but could you give me a couple of tips on the development of Instagram?

Best to start a new topic, and be clear what you are asking. I have no idea what you mean.

By "develop", do you mean develop a following on instagram?

I agree with Peter: start a new thread with the topic clearly indicated in the heading. I don't know how much of a response you will get, as I don't know how many people who frequent this forum use instagram. I don't.

Thanks for sharing this information. A lot of people post content on social media. However, few of them know how to take a good picture. I am working as an Instagram promoter, so the quality of content is pretty important for me. Whenever I post something online, I try to maintain a few standards that I believe are important. By the way, guys, since we are talking about social media, I wondered about your opinion about platforms like 1394TA. I have recently found out about the existence of these types of apps, and I want to know what you think about them.

Originally Posted by Strigoi

To achieve high-quality prints, there are a few key factors to consider.

Firstly, the number of inks used by the printer plays a significant role in determining the color gamut. Entry-level professional photo printers usually come with around 8 inks, while higher-end models can have up to 12 different inks.

Another important aspect is droplet size. Printers can deposit ink droplets of varying sizes, typically around 4 picolitres per drop.

The original post was about social media, not printing. If you have any issues it would be best to start a new topic

This may be of interest
https://en.wikipedia.org/wiki/JPEG

I believe that adjustable compression is part of the spec but wont be looking for the legitimate one. There is also mention of a lossless version but I don't think it's caught on, Compression levels could be looked at by saving in 8bit tif, I'm pretty sure 100% quality is still a lot smaller than that,

Webp as far as I know only figures on commercial sites,

Colour management exists on lots of machines these days but monitor calibration wont. The jpg's need a colour profile in them and in theory any profile could be posted, aRGB or any other,

I've only seen one comment on monitor calibration for social media on one site. A rather untidy uk one called NorthLight-Images. He views them with the monitor set for 160cd/m2 to get an idea what they will look like for many viewers but processes shots at the usual levels,