Where do the pixels go?

[hammysd]

I have been reading this forum for several months now with interest. This forum seems to have a very good handle on most of the information I use in my growing hobby. Now for the question -- where do the 6.3 million pixels go?

I take several pictures using the RAW setting with my 10D. I bring the files into my computer as RAW files. I then go to Photoshop CS and bring up the day's shooting using the browser. I select an image and it comes up in the RAW program under CS. I make a few adjustments and then "save" keeping in mind the choice of size of image at the bottom of this window. When I save this file using the default setting and bring up the "image size" under Photoshop I see my image is 240 dpi. If I save it as a larger sized image using the choices under the RAW program, does the program "resample" or just use the RAW pixels to make a bigger file? I think the latter.

The reason I think the latter is due to the fantastic performance I get when I print using my Epson 2200. I use 13 x 19 " semi gloss paper and the images are still sharp. I "expand" the image not by increasing file size but simply in the priniting process I ask the computer to fit the image to suit the size of the paper under preview. Does this choice "resample"? Again I think not because of the terrific results.

So the pixels must still be there even though Photoshop says it is only 240 DPI.

I then "step" grow the image to a larger size i.e. 20 x 30 and I still get very sharp images

Confused but getting great images.

Hammysd

[w10d]

I think you may be confusing file size and image resolution. When converting RAW files in Photoshop CS you have a range of images sizes you can output to - the native size captured by the sensor and sizes larger or smaller. If you choose one of the sizes larger or smaller, PS will add or remove pixels when producing this file from the RAW file.

In this context the image size is described in pixels High x Wide, e.g. 3072 x2048.

If you take an image this size and set the resolution to 100 ppi it will be described as 30.72 inches x 20.48 inches. Set the resolution to 1000 ppi and it will be 3.072 x 2.048 inches - BUT the number of pixels will not change, so no resampling. It might help you to play with the settings in PS's image resize dialog box: With and without resampling, and see what happens to the file size/number of pixels.

Hope that makes sense...

[hammysd]

We are on the same page. Thanks for the reply.

Yes, Photoshop does "add" pixels but that is exactly where I need your help perhaps in using the right words or in understanding. In the old days, when you "added" pixels there was a loss in sharpness especially as one expanded to poster size.

I now can print images poster size with no loss. I define poster size as 20" x 30". The poster I just printed out is photographic quality.

I "expanded" my image using Fred Miranda's Interpolation download program (excellent!). I am blown away by the sharpness of the image at this size. I started with an 8 x 10 image with 300 dpi resolution.

Next question: at what size of image does the 10D taken image using RAW start to break down i.e., you see pixelization?

Hammysd

[w10d]

I "expanded" my image using Fred Miranda's Interpolation download program (excellent!). I am blown away by the sharpness of the image at this size. I started with an 8 x 10 image with 300 dpi resolution.

Next question: at what size of image does the 10D taken image using RAW start to break down i.e., you see pixelization?

Hammysd

Firstly, if you are using Photoshop CS, Adobe has improved the interpolation process, and if you upsample using bicubic smoother the results are much better than using bicubic in earlier versions.

Secondly, there are many variables to take into account; the original image quality, subject, output device, etc. You might find that inkjet output with a resolution as low as 180dpi will show little or no quality loss (at normal viewing distances), allowing you to make the first resizing without interpolation (on a 300dpi image).

As for the limit, it will depend a lot on the image and the distance it is viewed from....