A question of size-(pixels ie chaps!!) (1 Viewer)

Re the queries yesterday with the problems altering the ppi or dpi as such,another couple of queries.
1).when checking some shots taken yesterday and going to the image re size box,the shots taken with the 4500+ scope showed up at 300 pixels.Even when changed to 800 for Gallery purposes,the pixels in the very bottom box were 300.Which means that if they are to be sent to the Gallery must be changed to 200 or less.Images taken with the 300d show up in the bottom pixel box at 180 or thereabouts.This is after both sets of images have been cropped and tweaked.So why is it,that the Canon with the larger no of pixels in its system sends smaller pixels to the pc.Both cameras are set to large files to be read to the card,and the Nikon has "fine" showing on the screen.
2) This brings me to a second query.I would like to frame a couple of images,which have been downsized to 800.(no,I do not have the originals before anyone asks!!).The images I would like to be A3 or the next larger,not sure which is the next size up.Will these images enhance okay,at A4 they are good.Do I need to leave all pics at the higher size to be enhanced for framing,inc any digiscoped ones wqhich are coming through at 300 pixel.By dropping the pixels to 200 (for Gallery purposes) does this mean I am lowering the quality.
The main reason for asking advice re the latter,is because I am going to have to find an online service to print higher than A4,and because I am not sure what is what,I do not want to waste money by paying for pics to be printed,then they all come back as rubbish,or not as clear as my own A4 ones.

Thanks,Christine.
thankyou for everyone who advised yesterday,having spent the morning sifting through cd,s I found one which should have contained the original,but it was moved to another file after it was re sized etc.Will not make that mistake again.

Firstly, different cameras will have a different number of pixels - my Nikon produces 3000x2000 (cpprox - can't remeber the exact size). I have a fuji which gives smaller images than this. Also depands on what setting - but "Fine" on one camera won't be the same as "Fine" on a different one.

I think you are also possibly getting confused between dpi and ppi. ppi as used on screen resolutions - it it the number of pixels per inch on your screen. dpi is a printing thing, as stands for dots per inch - the number of dots printed on the paper per inch. 1 dot does need equal 1 pixel.

With your re-sized pictures, i think you should limit the print size - you'll probably find A3 to be far too big. I tend to re-size my phots down to 1400x1000 and print these to A5 (approx 7x5 inches). Of course, i always keep the RAW (NEF) files which i store to TWO CDs - one i keep at home, and one i keep at work as backup.

To test the quality printing to A3 (which is twice A4), chop the picture (a copy of it!)in two, and print this to A4. Or print a quarter of the picture to A5. This will give you an idea of the quality you will get printing the whole image to A3.

Hope this makes some sense - it isn't easy to understand.

Christine, might be worth a look :
http://luminous-landscape.com/tutorials/understanding-series/und_resolution.shtml

Thanks for that link, normjackson that's explained a lot. I've bookmarked it for future reference

rezMole and Norma,many thanks.Yes I have earmarked the LL site.There is an awful lot of reading in there.I will try the half A4 print out.I picked up 2 used photo frames which will hold an A3 print,which is why I wanted to have a couple printed,as my printer only produces A4 max.I,m still somewhat muddled re the dpi's etc,but the LL site may help.
Again many thanks for your help.

I think that with this confusing dpi stuff, the best way to approach ALL image situations (not just for the web) is by thinking image size (width x height in pixels) first. This is always what matters. The dpi setting is just a reflection of how it will PRINT. For example, if you have a 1200x600 image and set it at 200 dpi, it will print a 6 inch by 3 inch (1200/200; 600/200) picture. Set the SAME image to 300 dpi, it will print a 4 inch by 2 inch picture. You haven't changed the image's size (it's still 1200x600).

That's why a 2 megapixel camera (which produces 1600x1200 images) only gives good printing results of max about 8x6 inches - setting at lower than about 200 dpi will give poor printings. A 3 MP camera can print bigger because 2048 x whatever when divided by 200 gives a bigger picture.

The confusing part is when you use an image program to "resize" an image. Some programs don't clue you in to the fact that there are 2 ways to "resize" an image. One way to resize an image is in the sense of PRINTING it at a bigger or smaller size, as I said above. I.e. if you increase its dpi (from 200 to 300) - gives you a SMALLER, but denser and sharper, print size. Decreasing the dpi gives a larger print. But you haven't really altered the size of the image in this case (it's still got 1200x600 pixels).

The other way to "resize" an image (sometimes called "resample") is to really change its size - say from 1200x600 to 600x300. In this case, you really have altered its size, by removing half its pixels. This usually requires a sharpening operation afterward to restore its sharpness. This type of resizing is what is done for web images - the image is smaller, and downloads faster. But it looks terrible when printed because it really has half as many pixels.

Therefore, when you use any resize/resample dialog box, if you only want to adjust the size the image PRINTS at, you should make sure that resampling is NOT being used (usually a checkbox). So, when you change the dpi, the image's dimensions (width x height in pixels) stays the same.

If you WANT to alter the image's size, say for the web, then you do want to use resampling. In this case, you should ignore the dpi. Again, what you should pay attention to is the dimensions. In the resize/resample dialog, check resample, and then change either the height or the width to what you want. Ignore what it says about dpi, since it is completely meaningless except when you print and is only confusing.

If you want to resize an image to be larger (i.e. ADD pixels to it, as opposed to printing it larger), you can do it with resampling up to a point, but not too much, because it has to invent pixels out of nothing.

Hope this helps. This IS a very confusing area.

Rah,many thanks for your detailed,but simply explained post.I have printed it,and I think that by following your instructions I will in future understand the process.Also many thanks to Scott,from Canada,and to Norma,who re edited the pics for me,they have now been sent to the professor from America who is compiling the book re plumage changes in birds,to see if they can now be submitted for printing.