Image res and printing sizes?

[Miss Jane]

I am really new to printing photos and selling them. Haven't done much since film days. I have been thrown in at the deep end with people wanting to purchase photos so have done a heap of reading and trying to get it right.
My problem is selling images when the res is too low for a certain size print.
But now the I have one that is a couple inches too small. How do I know what is the smallest res I can use and the photo still look alright? A couple of my images have been 3 - 5mb to start with but I have had to crop them out a fair bit and brought the size down to 620kb. Is there a way of increasing the res?

[arthurking83]

.... Is there a way of increasing the res?

ahhhhh! .. not really!

3-5Mb and cropped to 620kb is a monumentally monstrous mega crop!! :eek:

That is, you are basically going from a full sized image say 4000x3000 pixel (JPG) image down to a 1000x600 pixel (JPG) image without any recompression.
That's a significant crop, and not one to do with impunity.
That's similar to using a 50mm lens to achieve the framing of a 400mm lens. by cropping the image! That's pretty extreme.

I dare say that in this cropping and saving you have recompressed the image again, and used a lower image quality setting that you should have.(just a guess)

Post some images if you can to show us what it is you;re trying to describe.

You can do image upscaling(or uprezzing), but to a very limited degree. Maybe 10% increase without any loss of IQ. But this is assuming that the image has very high quality detail to begin with.

Unfortunately, when the final image is saved to a lower size resolution or compression level, you become stuck with it.

What I know about printing(not all that much really, but enough to get me by) is that it's not just a matter of how large you can print a file.
You need to take into account the viewing distance and the level of detail that is acceptable in the final print.

How much detail is in the relevant image will also determine how small the smallest res image you need for a certain sized print.

200-300 dpi(print quality) is what you should be aiming for for detailed images, and 150-200dpi where the actual details aren't as important as the overall 'scene' .. or the mood or artistic merit of the image as a whole.

so as an example of the required dpi of the printer to print the image with good to excellent detail.
If you use 200dpi on printer to print the hypothetical 1000x600 cropped image I referred to earlier, the largest reasonable sized print you could get would be 5x3 inches .. maybe 6 x 4 inches if detail level is required to be very high.
In the real world tho, you can print to a lower dpi level and still get very good image quality from the print.

My D300 has only 4000 pixels on the longest side, and at 200 dpi, it should should really max out at 20" as the largest print size before image degradation becomes a factor.
But the original image has good detail so that I had it printed to 30" on the longest side and all the individual blades of grass and petals of the flowers could still be easily and clearly be indentified.
ie. the end print resolution used was more like 150dpi which still gave 100% acceptable results on the print.

[Miss Jane]

Thanks for the detailed answer. i know it can be hard to comment without seeing the image. I will post my before and after tomorrow.
I cropped the head of a horse out from a distant photo (620kb after crop) and had it printed at 11x14 at BigW (for $1 it didn't matter what it looked like) and it was only really for me. Yes the pic looked a bit grainy or something up close, but at a distance it would be hard to notice.
That is why I think the image that has been sold might just pass as it is also 620kb 3.05" x 4.58" @ 250 PPI and the order is for a 6x8"

[arthurking83]

....
That is why I think the image that has been sold might just pass as it is also 620kb 3.05" x 4.58" @ 250 PPI and the order is for a 6x8"

because it's heavily cropped already using an effective 125dpi print resolution may not produce an acceptable print in terms of IQ.
If the purchaser is happy with the print due to sentimental reasons, then all well and good.

all that being said now, I would judge an image's print potential from looking at a Big W print tho!! :p
I'm not really knocking them, they do a reasonable job for those that have less particular needs, I've had prints done at OfficeWorks myself too, but they were cheap and for a purpose(and 6x4's!!)
At the same time, I also had a 12x8 printed up of the last known good image I'd shot.. just for the hell of it. At $2 or so, why not ;) I was already there getting my mum's 6x4 prints.
But a higher quality printing service would probably do this 640kb image printed to 6x8 some justice.

anyhow I hope it works out for 'ya.

[Miss Jane]

Here is the cropped and uncropped. It is being done by the printshop through photomerchant. I think i need to go through and delete any low res images to avoid this next time.