About Alex Gray Expertise I was Chairman of the UK Corel Users Association which had upwards of a thousand individual and corporate members), and Editor of Corel User journal (back issues for sale!)
I now run my own graphics business and also manage a local radio station, and continue to use PhotoPaint heavily. I also have wide general computer and networking expertise.
Question I work with Corel Photo Paint 9, and create digital designs, which I have printed on tshirts.I am NOT a professional graphic artist, and am totally self taught. I have been successful in converting .CPP (corel photo paint file types) to .jpeg and then uploading to companies on internet for tshirt creations. My Question:
Until now, I have somewhat comprehended the concept of resolution/pixel/inches sizing, but suddenly I got confused. Can you clarify for me?
Here's an example of a question I asked a tshirt company on the web, due to some confusion:
My question:
If you recommend pixel size of 900 x 700, I am assuming that is at 150 resolution which calculates to an image size of: 4.6667 x 6 inches.
By the way, all my images are 8 x 10 inches at 300 resolution which calculates to a pixel size of: 2400 x 3000.
Their answer was:
Actually, by my calculations 900x700 translates to 9+ inches by 7+ inches.
THIS CONFUSES ME:
900 x 700 pixels, before coming to the size (inches) calculation, don't you have to factor in the RESOLUTION? I would think if 900 x 700 pixels at 100 resolution would equal 9x7inches, but at 150 resolution or 300 resolution don't (inches) the size change?
Thanks in advance for your help.
Answer Marlene
It sounds as if your understanding of the concept of resolution/pixels/inches is perfectly clear and correct.
Many people, even long time 'professionals' have completely muddy knowledge of these matters, largely thanks to 'helpful' software insisting on showing sizes in inches or millimetres rather than pixels, but it's clear from your question that you have a clear understanding of the matter.
Maybe the only mistake you have made is to assume that the T-Shirt company was working to 150 dpi. If their calculations tell them that 900x700 pixels is '9+ x 7+ inches" then they may well be working to a screen resolution of 96dpi. It may be that they have no idea about dpi and trust what their computer tells them is the 'real size', which it may be basing on their default screen resolution.
To summarise what you already know:
a) The only physically fixed dimensions that a bitmap image has are the number of pixels wide and high in the image (eg 900 x 700 pixels)
b) You can choose to reproduce that bitmap at any physical size, simply according to how large each pixel is made at the time of printing. For example, if each pixel is printed 1/100th of an inch wide, the printed 700 x 900 image would be 7" x 9".
c) Resolution is a measure of how accurately defined an image is, in terms of how many pixels appear in each unit of width or height. The effective resolution in dpi of the final printed image is therefore just the actual width of the printed image divided by the number of pixels shown across that width (ie 100 dpi in the example above).
d) Software may allow you to attach a dpi value to a particular file, or may attach one by default (typically 72 or 96 dpi for a screen oriented application, or 300 dpi for a profession print oriented application). But this number is entirely arbitrary and serves only one purpose - it is to allow the software to represent dimensions in 'real world' units such as inches, rather thna pixels. It does not alter or control the definition of the image itself, merely what dimensions will be shown on the display and, usually, what default printing width will be used.
e) in colour printing there are further issues related to the 'screening' or 'ruling' colour separation processes used to represent colour in print. These are usually measured in lpi (lines per inch) and are not the same as the dpi of the image. As a rule of thumb, for any given screen ruling (typically 100-175 lpi), the source itmap images should be reproduced so as to provide a resolution in dpi at around twice the screen ruling in lpi (typically needing a resolution of 250-300dpi for professional colour work).
I hope that helps - I know this is a topic that causes a lot of grief, and is often misunderstood, or at least misapplied by professionals as much as by the self-taught (actually, in my experience, many 'professionals' are also 'un-taught'!).
