buckscop wrote:
Amateur. Canon T7i. Usually jpg, sometimes raw & jpg. Besides cropping for composition, I generally crop all my keepers at a 6"x4" size with PSE when processing. am i doing my images an 'injustice' to crop to that size versus a larger size, or does it not matter. I'm sure i picked that way back due to the size i would print out pictures at home. I do very little home printing nowadays, so if cropping, is there a better size? Most of my work gets put on electronic picture frames, emailed to family, or ends up online. I do some canvas printing, usually 16x20, but probably had already cut it to 6x4 when PSE processing originally. Thanks.
Amateur. Canon T7i. Usually jpg, sometimes raw &a... (
show quote)
Are you actually "cropping" the image?
The size info you have provided is incomplete and doesn't really tell us.
What's important is the pixel dimensions of the image... or the pixels per inch.
For example, your 24MP camera natively makes 4000x6000 pixel image. If you simply change the "size" of the image to 4x6", but leave the resolution unchanged, you can end up with 1000 pixels per inch and the image is still 4000x6000 pixels. Or if you change the image to 16x24", leaving the resolution unchanged, it will be 250 pixels per inch and still 4000x6000 pixels. Either way, you actually haven't "cropped" the image at all!
You need to size your images primarily for their pixel dimensions.
For online sharing and digital display, usually 100 pixels per inch is a good choice, since that's close to the resolution of most monitors or LCD displays. A 4x6 at 400x600 pixels will load quickly and can be easily attached to an email. On most monitors a 400x600 pixel image will display 4x6" (it will display a bit smaller on 4K and higher resolution monitors). This assumes that whatever is being used to display the image is set to its native resolution (it's possible to change that, but you have no control over what people do with their computer monitor... so no need to worry about it).
For printing you should size images at a higher resolution. Many inkjet printers use around 240 pixels per inch optimally... Commercial printers can use the same, but may be fine with a little less or,for some processes may even require a little more (ask the printing service for their recommendation). You mention printing on canvas, where the coarse texture of the print medium will probably make a fine looking image with as little as 170 pixels per inch or possibly even 140 ppi. For printing on smooth matte paper I usually use 300 ppi... more than necessary, but a round number that's a lot easier to calculate in my head.
Once you determine the resolution you want in pixels per inch, then you can set the size in inches.
Reducing the SIZE of your images to something less than the native resolution of your camera for printing or display will tend to make the images appear sharper and hide any minor focus error. It's also possible to increase resolution of an image to make bigger than the native resolution... "up-rezzing" them. When that's done, the software is adding pixels to the image by "interpolation".... using the adjacent pixels as a guide for the new ones it creates (that's a somewhat simplistic description of the process). For example, let's say you want to make a large 24x36" print and are using an inkjet process where 240 ppi is recommended.... in that case you would be increase your camera's native 4000x6000 pixel image to a 5760x8640 pixels (240 x 24 and 240 x 36).
Of course, maybe you actually are also cropping the image itself... using only a portion of it. For example, making an 8x10 print will always require that some of the longer dimension be "trimmed" off, even if you don't trim some of the short dimension, too. That's because of the different "aspect ratios"... 3:2 versus 5:4.
Or maybe you want to magnify part of the image and trim off other parts of it, just to improve the composition or eliminate some distraction from the edge of the image... or even just to straighten an image a little.
Actual cropping, for whatever reason, has to be done judiciously. At some point, you'll be trimming off and "throwing" away too much of an image for it to be usable. How much cropping is possible depends upon your end use and the quality of the image you need. You mention converting an image from horizontal to vertical, for example. At a minimum, that means you're going from the 4000x6000 pixels (24MP) of the original image to 2666x4000 pixels (10.7MP).... In other words you are trimming off and "throwing away" approx. 55% of the image. That probably would be no problem if making a 6x9 or moderate size image for online display... but is no longer going to be sufficient for a 16x24" print! If you also using cropping to "zoom in"... further cropping the image... at some point image quality will start to degrade heavily. The image will become "pixelated". Minimize the amount of cropping whenever possible, for the best image quality.
If you are applying noise reduction, I recommend doing that early in your post processing, before reducing the resolution of your image at all.
Conversely, any sharpening to the image should be done as one of the last steps, after the image has been cropped and resized for it's intended use. This is so that you can adjust the sharpening to avoid problems such as artifacts that sharpening can cause in images.
Simply keep your RAW files.... Those are your "original" and complete images. You have to convert RAW to some other sort of file to use them anyway. RAW cannot be viewed directly or printed. They must be converted to a JPEG or other file type, first. And those conversions can be any size, resolution, crop or aspect ratio you want or need for a particular purpose, without any changes being made to the RAW original. So you can always go back to the RAW and create another file that's sized and/or cropped differently. If you shot JPEGs only, then you'd want to set aside originals of those. If shooting RAW + JPEG, feel free to size those JPEGs any way you wish. You can always generate a new one from the RAW file.
Finally, don't conflate image "pixels per inch" resolution with printing "dots per inch". They are not the same thing. With many print processes, the printer lays down three (or more) dots for each pixel in an image. As a result, the resolution of a printer is often triple that of the image.