Photo Quality: DPI discussion continued..

[cellentani]

I didn't want to derail minousbijoux's thread, but I'm very interested in continuing the discussion on web photo quality.

It was my understanding that DPI had to do with real physical size, and had no bearing on what you see on your computer screen - i.e., the same image at 72 DPI and 350 DPI wouldn't look any different on your computer monitor. It IS a size measurement, but only relative when dealing w/ physical inches like scanners and printers. To test, I resized an image to 520 x 484 pixels, and saved once at 72 dpi, and again at 350 dpi - absolutely no difference in image quality or file size. However, I have no idea if this has any bearing on the zoomability that VapidLapid mentioned.

As mentioned in the other thread, I too have noticed a difference in image quality when I upload photos, and I always assumed that PS and FB resampled my images. I've often wondered if it was possible to submit images that wouldn't require resampling, and if so, what those perimeters are. Zeolite posts some of the crispest photos I've seen - I sure wish I knew how he edits his photos!

Kenny, you also have great photos - out of curiosity, what what do you normally resize your images to?

Maybe I'll upload an image at various sizes and quality.....might be interesting.

 

[VapidLapid]

It is true that your screen will only display 72 dots per inch. If you enlarge your browser window on a file that is also at 72 dpi you are enlarging the dots per inch rather than seeing a larger picture with more dots. if the file is saved at a larger resolution, the enlarged window will improve resolution up to the saved dot per inch specification. After that it will start enlarging the dots. Enlarging the dots does not improve resolution; making more of them does.

 

[minousbijoux]

Cellentani:

Feel free to derail! I only posted my pics to complete the thread. But really, I am a confused digital photo beginner and need all the help I can get!

I also would like to know how to maintain the color, as either it desaturates, or it makes purples blue, oranges red, greens yellow, you get the idea - does this have anything to do with DPI?

 

[cellentani]

Thanks Vapid, that's what I thought.

For starters, I uploaded 3 images, all 640 x 752 and 415KB, but at varying DPI's. To me, they all look the same on my monitor, but Vapid and MB, can you tell if there's a difference if you zoom in?

 

[minousbijoux]

I see that I love that pendant; beyond that, I see no difference. But another question, how do you take pics like that indoors and have the colors appear so accurate? Are you using a tripod or mechanism to balance the camera?

 

[VapidLapid]

There was no difference in dpi resolution in your three pictures. This is likely because your pictures began as 72 dpi whether in your camera, or perhaps the first one you did was saved at 72 dpi and then you made the others from that. You cannot add resolution where it does not already exist. if your file is 72 dpi to begin with you may save it a 3000 (absurd for anything) but it will still be 72 dpi because that is all the information you have. I downloaded all three of your files and opened them in photoshop so I could get information about them.

 

[cellentani]

Next comparison: I've saved the files in different pixel sizes, but they have both been saved at the highest quality/resolution. See if there's any difference in visual quality.

 

[VapidLapid]

It matters tremendously that each of these samples is made from the same original "mother" file

 

[VapidLapid]

If all our image files contained all the information about each pixel and within each pixel all the information about color tone hue saturation and grayscale, then dpi would correlate well with image size. since that would make for unwieldy large files there was a need to have systems (programs with algorithms) that could compress that data to make the files smaller without altering the image quite so much to our apparent perception. Every program compresses in its own way, but imagine if you will an image with little difference in a 25 pixel block. Some algorithms might remember the shape and size of the block and the average color for the set and assign that to the whole block, thereby reducing its memory load by 24/25ths. The area covered is still 25 pixels, but now the computer only has to remember one of them. That is an oversimplified example of compression and it's difference from dpi.

 

[cellentani]

There was no difference in dpi resolution in your three pictures. This is likely because your pictures began as 72 dpi whether in your camera, or perhaps the first one you did was saved at 72 dpi and then you made the others from that. You cannot add resolution where it does not already exist. if your file is 72 dpi to begin with you may save it a 3000 (absurd for anything) but it will still be 72 dpi because that is all the information you have. I downloaded all three of your files and opened them in photoshop so I could get information about them.

Vapid, to alter the DPI, I started with my original, raw cr2 image each time, and changed the DPI field when converting to jpg. Perhaps this means that PS converts the DPI when you upload images, or, since your screen resolution is 72, any image you save won't be above that? I'm not sure, but I just don't think DPI affects how well you can zoom and still see an image clearly.

 

[cellentani]

It matters tremendously that each of these samples is made from the same original "mother" file

I know, and yes, they are all from the same mother file.

 

[VapidLapid]

It does. Perhaps your camera is set to capture at 72dpi. What is your camera?

It is also possible that PS reduces dpi in addition to compressing other data

 

[cellentani]

I see that I love that pendant; beyond that, I see no difference. But another question, how do you take pics like that indoors and have the colors appear so accurate? Are you using a tripod or mechanism to balance the camera?

Thanks Minous! Making sure there is as little movement as possible in your camera and subject is crucial to indoor or low-light photos. I don't use a tripod, but I do stabilize my camera on something, and I notice that I hold my breath when depressing the shutter, lol.

 

[cellentani]

It does. Perhaps your camera is set to capture at 72dpi. What is your camera?

It is also possible that PS reduces dpi in addition to compressing other data

I have a Canon S95, and it doesn't capture images at ANY DPI. In fact, when I convert raw images to jpg, I can leave the DPI field blank, and it makes no difference.

 

[VapidLapid]

But it does. the sensor on that camera is 3648 x 2739 pixels and is one inch on the short side. The maximum dpi then is 2739 per inch.
the menus where you can chose Fine, Superfine and Normal all effect dpi though they dont say so explicitly. Also the menu below that gives you choices of L, M1, M2, M3 and S which also and explicitly effect dpi.

And it is a nifty little camera!

 

[0-0-0]

http://www.rideau-info.com/photos/mythdpi.html

http://en.wikipedia.org/wiki/Pixels_per_inch

http://en.wikipedia.org/wiki/List_of_displays_by_pixel_density

Dpi/ppi settings alone have no bearing on how images appear on screen.

Most sites like PS, FB, etc. resamples uploaded pictures to reduce file size.

 

[cellentani]

But it does. the sensor on that camera is 3648 x 2739 pixels and is one inch on the short side. The maximum dpi then is 2739 per inch.
the menus where you can chose Fine, Superfine and Normal all effect dpi though they dont say so explicitly. Also the menu below that gives you choices of L, M1, M2, M3 and S which also and explicitly effect dpi.

And it is a nifty little camera!

I thought Fine, Superfine, and Normal have to do with the amount of a camera's compression to jpeg, and doesn't affect pixel size. How does that affect dpi?? And even if it did, what bearing does that have on web images?

 

[kenny]

Kenny, you also have great photos - out of curiosity, what what do you normally resize your images to?

Simple question . . . complicated answer.
Sorry.

Good results is the result of EVERY step going well.
It's like a chain which cannot be stronger than its weakest link.

First of all I have lenses and equipment that can enlarge the diamond (and even a laser inscription) much larger than life size before the image even gets INTO the camera.
Cropping in or zooming in AFTER the pic has been taken is not as good since it does not use all the pixels available one your camera's sensor, just the ones in the middle.
Another way of looking at it is cropping later is like downgrading your 15 MB camera to a 5 MB camera.
Filling up the screen in the camera and using max pixels via true macro lenses/extension rings/bellows/lens-reversing adaptors is so significant that even if I screwed up every step after that I would probably STILL get excellent results.

FWIW here's what I do:

My camera is set to capture images in RAW format.
This gives you uncompressed and huge files that have MUCH more flexibility when it comes time to use software to optimize the image after the pic is taken.
If your camera does not have RAW format set it to the highest image quality possible.

I have an iMac and use the free software it came with, iPhoto which I like better than Photoshop for my simple needs.
I connect a USB cable from the camera to the mac and turn on the camera.
This launches iPhoto and I import the pics.

I open each one and optimize it (Brightness, contrast, highlights, shadows, white balance etc.) till it looks as close as possible to the way I rember the diamond looking in real life.

Next I go through an unusual process that results in the highest resolution that PS will accept . . .
Instead of saving the pic as a jpg I do a screen capture on my Mac using SHIFT COMMAND 4. (I have no idea how to do this on a PC.)
This creates a PNG file and places it on my desktop.

Without opening the new PNG file I right click on its icon and select "Get Info".
This brings up a pop up screen that tells me the file size, such as 2.7 MB or 925 KB.
PS can accept files up to 2.0 MB.
The larger the file the more data (resolution, sharpness, detail, crispness, clarity) it has.
I do not pay attention to DPI and I don't need to; I don't think iPhoto even allows me to.

If the file is over 2.0 MB I throw it away, go back to iPhoto and start over by making the iPhoto window smaller - by single clicking the lower right corner and dragging up and to the left and letting go.
Then I do another screen capture and check on its size.
I do this till I get a file size of around 1.9 MB.
Remember, 2.0 MB is the highest resolution (largest file size) that PS can accept.
I don't care about DPI or about how many inches of my screen it takes up.
Those don't matter when you use this process on a Mac and iPhoto.

The results are excellent.

 

[cellentani]

Thanks Kenny! I wonder if the compression is different on a png vs. jpg file.

 

[kenny]

Thanks Kenny! I wonder if the compression is different on a png vs. jpg file.

I think PNG is more accurate than even the highest resolution JPG.

TIFF is better but PS software cannot recognize TIFF files.

 

[cellentani]

Thanks Kenny! I wonder if the compression is different on a png vs. jpg file.

I think PNG is more accurate than even the highest resolution JPG.

TIFF is better but PS software cannot recognize TIFF files.

And that would make sense, since there isn't any compression w/ PNG (had to look it up). I think I'll try another comparison tomorrow. I'll use a gem photo so I can stay in this forum, lol.

 

[0-0-0]

I just did my own test and it looks like PS resamples images over 480 pixels in height. So keep image height at 480 pixels or less if you don't want PS to resample for you.

Original is 400x400px, 180ppi, 119,274 bytes
PS is the same


Original is 400x400px, 1ppi, 119,274 bytes
PS is the same


Original is 480x480px, 180ppi, 164,774 bytes
PS is the same


Original is 480x480px, 1ppi, 164,774 bytes
PS is the same


Original is 800x800px, 180ppi, 430,670 bytes
PS resamples to 480x480px, 96ppi, 160,180 bytes


Original is 800x800px, 1ppi, 430,670 bytes
PS resamples to 480x480px, 96ppi, 160,180 bytes

 

[cellentani]

Thbmok, that was super helpful and you just saved me a lot of work!

 

[minousbijoux]

So in summary, what's the conclusion? what can I do that is different other than to do it Kenny's way and work from screen captures?

Can someone break it down into simple component parts for those us who aren't fluent in the terminology?

 

[zeolite]

thbmok wrote:
I just did my own test and it looks like PS resamples images over 480 pixels in height.

Actually, PS resamples if the longer dimension is more than 640 pixels, and it also resamples if the shorter dimension is more than 480 pixels. In thbmok 8 gemcase picture in this thread

[URL='https://www.pricescope.com/community/threads/how-much-head-reflection-is-acceptable.165443/']https://www.pricescope.com/community/threads/how-much-head-reflection-is-acceptable.165443/[/URL]

the image is exactly 640x480 pixels. I determined this by downloading the PS image, and measuring image size in Photoshop.

 

[pregcurious]

Celletani, is that pendant yours? It's beautiful!

 

[zeolite]

Kenny wrote: Instead of saving the pic as a jpg I do a screen capture on my Mac using SHIFT COMMAND 4. (I have no idea how to do this on a PC.)
This creates a PNG file and places it on my desktop.
Without opening the new PNG file I right click on its icon and select "Get Info".
This brings up a pop up screen that tells me the file size, such as 2.7 MB or 925 KB.
PS can accept files up to 2.0 MB.
The larger the file the more data (resolution, sharpness, detail, crispness, clarity) it has.

You can learn about PNG is this Wikipedia thread:

http://en.wikipedia.org/wiki/Portable_Network_Graphics

Quoting from Wikipedia: JPEG (Joint Photographic Experts Group) format can produce a smaller file than PNG for photographic (and photo-like) images, since JPEG uses a lossy encoding method specifically designed for photographic image data, which is typically dominated by soft, low-contrast transitions, and an amount of noise or similar irregular structures. Using PNG instead of a high-quality JPEG for such images would result in a large increase in filesize with negligible gain in quality.

Kenny wrote this excellent thread, showing his camera skills with macro and reversed lenses:

[URL='https://www.pricescope.com/community/threads/do-you-want-super-sharp-close-up-pics.168499/']https://www.pricescope.com/community/threads/do-you-want-super-sharp-close-up-pics.168499/[/URL]

He may have uploaded a nearly 2MB file, but after Pricescope compressed it, it is at 254.56 KB, which you can read just below the first picture.

Here is a purple sapphire I’ve shown before. It is 500 x 400 pixels and is 87.8 KB, and yes, it is a compressed jpeg file. The 2MB PNG file is 22.8 times as large as my jpg file.

 

[zeolite]

cellentani wrote: As mentioned in the other thread, I too have noticed a difference in image quality when I upload photos, and I always assumed that PS and FB resampled my images. I've often wondered if it was possible to submit images that wouldn't require resampling, and if so, what those parameters are.

Yes, pictures should be 640x480 pixels or smaller.

Cellentani wrote: Zeolite posts some of the crispest photos I've seen - I sure wish I knew how he edits his photos!

Thank you for your kind comments. Like Kenny says, it is a chain of events, with each link adding to the final picture quality.

1 For most people, use a tripod. In your case though, it won’t help as much since your S95 has special Canon technology. From the Canon website:

Genuine Canon lens with Hybrid IS
The PowerShot S95 … Canon’s acclaimed optical Image Stabilizer (IS) counteracts camera shake – reducing blur and enabling users to capture shots in darker conditions and shoot at a shutter speed approximately 4-stops slower than would otherwise be necessary to achieve a blur-free shot. Hybrid IS also prevents image blur during close-up shooting, counteracting angular and shift shake that becomes more pronounced during macro photography.

2 Shoot in Canon Raw, not jpeg format; your S95 can shoot raw. As Kenny says “This gives you uncompressed and huge files that have MUCH more flexibility”. This means you can alter contrast, color, exposure and white balance, AFTER the picture is taken.

3 Use a DSLR camera. D is for digital, SLR means single lens reflex. These are heavy expensive cameras with interchangeable lenses. DSLRs allow you to view through the photographing lens, allowing to you to choose where to place the focus, with an accuracy beyond a point and shoot camera.

4 DSLR also allow you to use a lens specifically designed for close-up photography. While this sounds great, I think the lenses in most point and shoot cameras are excellent.

5 Use a photo editing program that allows you to set different levels of jpeg compression. This is different that just setting the image size, such as 640x480 pixels. For example, Photoshop gives you 12 different levels of compression. I use level 10 for 300 dpi prints, and level 7 or 8 for web pictures.

6 Sharpen the picture correctly for the intended use. Sharpening is not at all the same as compressing or resizing. Read this:

http://ronbigelow.com/articles/sharpen1/sharpen1.htm

Sharpening for 300 dpi prints is different than for web pictures. While most photo editing programs offer sharpening, I use a special program that makes it easier for me: PK Sharpener

http://www.pixelgenius.com/sharpener/

You can use this program for free for 7 days to decide if you want to buy it.

Sharpening specifically for web use is a HUGE improvement for web pictures! If I could only name three ideas for you, cellentani, without buying an expensive DSLR camera, I would suggest shoot in Canon Raw, control the amount of jpeg compression, and learn web sharpening or buy this program and use it.

 

[minousbijoux]

Zeo, and for me and other Nikon Coolpix 6000 users? Any tips, other than hire a photographer to take photos of my stones?

 

[zeolite]

Zeo, and for me and other Nikon Coolpix 6000 users? Any tips, other than hire a photographer to take photos of my stones?

Concerning raw, look near the bottom of this link:

http://en.wikipedia.org/wiki/Nikon_Coolpix_series

Under raw image format:

P6000 (discontinued) – NRW format

I don't know this format but, it does look like it shoots a discontinued raw format

Ask the Nikon guys, they know much more about Nikon than I do.

As I read farther, why is there a Coolpix 5XXX and 7XXX, and no 6XXX listed?