Do the image pixels remain the same pixels when i print it on paper?

% another question, Does the paper quality affect the image pixels?

[Rik]

The answer to both questions heavily depends on your printer and the image. I doubt it is possible to give a general answer.

What is your underlying question? Why is this relevant for you? What makes this a Matlab question?

[Mostafa Taleb]

I'm working on project in matlab , hiding information in an image.

Answer 1

[Walter Roberson]

What you see on the screen is Additive color, but what you see on paper is Subtractive color. Printers need to convert between the two color spaces. However, RGB color schemes do not give enough information to convert uniquely.

There are systems such as Pantone that attempt to compensate. Pantone is not inherently a science though: it is more a whole series of reference points that vendors are expected to do whatever it takes on their end to reproduce.

There are science based methods to describe color in more detail. At the moment I do not recall if they need one extra or two extra parameters beyond RGB.

The quality of the paper does matter, along with how glossy or mate it is, and also its color.

[Mostafa Taleb]

I appreciate your help. Whenever I have a problem with Matlab, I look for a solution and find your perfect answers, so I want to thank you. Regarding the questions, I am working on a project to hide information in an image. I completed the project electronically(matlab work). Only work on printing on the paper remains, can you help or do You have tips for a printer or device that prints images while maintaining resolution.

[Walter Roberson]

Do you happen to have access to an "All-In-One", combination printer and scanner? Or were you planning to take pictures of the printed image with a cell phone?

Printers are often 600 dpi or more -- though you have to be careful about what kind of dots are being discussed (some manufacturers talk about "microdots". Printers that use ink of some kind usually cannot control the thickness or chemical makeup of a droplet, so printers often have to use microdots arranged in a halftone pattern in order to simulate intensities.

Phones such as Iphone X or Iphone 11 (non-Pro) are 12 megapixel, which is about 4000 x 3000. We can quickly see that if your printed image is more than 5 inches at 600 dpi, then 3000 pixels would not be enough to capture it at full resolution. If the printer is operating at 1200 dpi, then you get 2 1/2 inches. I just experimented with a 5 inch piece of paper on my cell phone at 4000 x 3000: it was tricky to get the paper centered in the view without getting significant problems with perspective (indeed, I could not manage: 4k resolution does not necessarily mean that the 4k pixels are located along a viewing plane that is useful for your purposes.)

[Mostafa Taleb]

After printing the image from the printer, I plan to take a picture of it, start with the type of printer, do you know the name of a specific printer?keeping possible can resolution? Do you know a certain quality of paper that will suffice? I'm so grateful with your help

[Walter Roberson]

Hmmm... it might not matter all that much what you use, beyond a minimum, provided that the printer is consistent.

If you use A4 paper then the printable area is about 8 inches by 11 1/2 inches.

If your printer resolution was as low as 200 dpi, then you would get about 1600 pixels wide by 2300 wide.

If your original image was up to 1500 x 2000 pixels (7.5 inches by 10 inches) then with a 12 megapixel camera that was well positioned, you could hypothetically photograph at 2 camera pixels per printed image pixel (in the 200 dpi case). However, you would have to make sure that you photographed as "Raw" because typically phones store as JPEG and JPEG is a lossy compression algorithm that complicates everything for you.

In the 300 dpi case, an image of the same physical size would be up to 2250 x 3000 pixels, and your 12 megapixel camera could only average 4/3 camera pixels per original pixel.

So questions would include what the resolution of the cover image is, and what resolution of camera you have available; those together would permit us to calculate the printer resolution needed.

[Mostafa Taleb]

The available camera is 13 MP, and the cover image with dimensions of approximately 2000x1500 and may be less than these dimensions, but I save every cover image in png format, but phones save the images in jpg format, as you said.

[Walter Roberson]

"13 MP" looks likely to be 4208*3120 resolution, so with 2000x1500 .

What kind of phone will you be using? My Samsung offers a RAW setting when shooting is done in PRO mode. I find an article on creativepro.com talking about apps that can shoot RAW on iPhone (but there is a technical issue that applications need to specifically work around.)

With careful positioning, you should be able to get more than 2 camera pixels resolution per image pixel.

If your data density compared to the cover image is not high, you should be able to embed the data at the Discrete Cosine level, which would survive reasonable levels of JPEG compression.

[Mostafa Taleb]

My phone, Samsung Galaxy A10s, I don't think it has RAW settings, but there are apps in the PLAY Store. You say that, after hiding the data in the image, press the cover image with dct, is this what you meant?

[Walter Roberson]

Use the Samsung "Camera" app (built in to the operating system.)

Launch the app so that it is ready to take pictures in the normal way.

Look in the upper left corner. You will see a "cog-wheel" icon to the far upper left, the left-most icon. Click on that. That will bring up Camera settings.

The first couple of settings are about "Intelligent features" like scene optimizer. Skip those ones.

The second group of settings is labeled "Pictures". In that section, the first setting is for Rear picture size, and (at least on my phone) the second is the Front picture size. Go down to the last of the settings in that small section, which will be "Save RAW copies".

If you enable that setting, then when you use Pro mode, then the software will save RAW files as well as JPEG files -- but only when you are using Pro mode.

To enable Pro mode, go into the page where you would be ready to take a picture. Near the bottom, you will see three larger circular icons. The left circle is to view the previous picture that was taken. The center circle is the button to push for shutter. The right circle is for switching between front and back cameras.

Now look at the line of text above those three circles. By default the left word in that line is "SINGLE TAKE", and then you have "PHOTO". Then there is "VIDEO", and then there is "MORE". Those words are for selecting camera mode. Click on "MORE".

Now, in the page that comes up, there will be a number of camera modes, including FOOD and NIGHT and SUPER SLOW_MO. You want to click on the one that looks like a stylized leaf-shutter with the word PRO beneath it. That will get you into PRO mode.

But before you leave that page showing all the different camera modes, notice the "pencil" icon near the bottom right, in line with the "PHOTO" "VIDEO" "MORE" line. Click on that pencil. Now go up to the PRO icon and drag it down to the right of the word "VIDEO". And then click SAVE. Once you have done that, then in the main camera app window, to the right of the "PHOTO" "VIDEO" words, there will now be "PRO" as well; that now gives you a quick way to access PRO.