Using a size template in GIMP for paperback cover creation

This post is based on a rough note prepared as reference for me for cover creation in 6 in. x 9 in. paperback books I publish using self-publishing platform --name-snip--.

I thought of putting up this post publicly as I think it may be useful to some others. I have --name-snipped-- the name of the concerned self-publishing platform to avoid any sensitivity.

Note that Pothi.com (another self-publishing platform I use) cover creator works well for Pothi.com books. Further Pothi.com wrote me (which I shared publicly here  https://ravisiyer.blogspot.com/2019/06/pothicom-is-great-self-publishing.html) that they have no objections to the output file of their Cover Creator tool being used elsewhere (provided all the cover content is mine).

I ran into problems on using --name-snip-- cover creator. So there may be situations where I may need to either create/modify a cover to be submitted to --name-snip-- (perhaps created using Pothi.com cover creator tool) using tools like GIMP and Paint.

I had to modify the iami book (my Who am I? I am I ... book) cover for A5 size used in Pothi.com to 6 in x 9 in size used for --name-snip-- books. That had to be done using tools like Paint and GIMP. This note tries to capture some learnings I had from that effort (and slightly more).

The process is imperfect. The context of this note is a paperback book I am additionally publishing using --name-snip-- in 6 in. x 9 in. size with 112 pages inner content, which was first published using Pothi.com in A5 size with 123 pages inner content.

1) --name-snip-- provides a template guide PDF document (as part of a zip file). Crucially that does not provide spine size. So this cannot be used as-is as an exact template in GIMP or Paint to create/modify a cover.

2) However the PDF document can be imported into GIMP where the sizes stated in the PDF seem to match with how GIMP shows it. The spine left black area border and right black area border seem to be 0.06 inches (perhaps it is 0.125/2 i.e. 0.0625 inches) in size, in comparison to the left and right black area border of back page and front page which are 0.125 inches in size. Note that there is an additional 0.125 inch on the left and right extremes of cover page.

In other words:
a) First from left black border area width is 0.25 inches
b) Second from left black border area width (just before spine inner area) is slightly less than 0.19 inches (perhaps it is 0.125 + 0.0625 i.e. 0.1875 inches)
c) Third from left black border area width (just after spine inner area) seems to be slightly less than 0.19 inches (perhaps it is 0.125 + 0.0625 i.e. 0.1875 inches)
d) Fourth from left black border area width is 0.25 inches

An issue is that the PPI is 100 for the converted from PDF image in GIMP. Change this to 300 (see 'Additional useful stuff' section below for how to do it). Pothi.com insists on minimum of 300 DPI (I think PPI is closely related to DPI) for images in paperback book content, including paperback cover page.

3) A solution to make the --name-snip-- provided template an exact template for a particular book cover, is to modify the template by adjusting/modifying the inner spine width (and width alone) in the template to estimated spine size based on number of pages in the book and thickness of paper used. Now this may not be an exact spine width calculation for the book printed by --name-snip-- but may be good enough for at least the initial version of cover design. --name-snip-- does not seem to have a page providing us the spine width calculation. But I think this web page calculator can be used: https://www.gutenberg.com.mt/spine-width-calculator

These are the calculations for the 6 in. x 9 in. iami book:

Paper Weight: 70 GSM
Paper Volume: Uncoated
Page Extent: 112
Cover: Paperback
Result (Spine width): 6 mm

6 mm is 0.236 inches

I don't know if Uncoated is the right selection for cream paper which is what I have selected for iami book on --name-snip--. But I think Uncoated will give a reasonably close to actual figure and so can be used for at least first version of cover design.

I wonder if --name-snip-- will provide spine width over email for these criteria (112 pages of cream 70 GSM paper).

4) The spine inner width in the --name-snip-- template image (imported from pdf) seems to be 0.42 inches. So the template image's spine width has to be reduced from 0.42 to 0.236 (or 0.24) inches.

5) GIMP process for selecting right part of book template image and moving it to the left to reduce spine size in it:

a) The left spine border area gets over at 7.29 inches or perhaps 7.2875 inches. So the right spine border area should start at 7.2875 + 0.236 = 7.5235
b) Choose Tools -> Selection Tools -> Rectangle Select. This changes mouse pointer to Rectangle select icon.
c) Have a selection area of front cover page and associated border area and little more.
d) Right click in selected area and choose Select->Float
e) Use left mouse cursor to position left edge of selected area at 7.52 (in original template it is at around 7.7 (or slightly more like 7.71). Note that one can expand the zoom to 800% and so achieve precision move to 7.52 using left cursor.
f) To finalize the move, Choose Layer->Anchor Layer.

6) One can add a pic as an overlay onto the template by opening the pic in a separate GIMP window, copying it, and then pasting it onto the template.

To scale the pasted pic (have not figured out how to enforce proportional scaling to prevent distortion): Right-Click and then choose Tools -> Transform Tools -> Scale.

Enter key is supposed to commit the scaling operation. I additionally would choose Rectangle Select and check that the scale icon in cursor goes off.

Layer -> Anchor Layer commits the transformation

Right-Click and then choose Tools -> Transform Tools -> Move ... for moving a selection.

As earlier, Layer -> Anchor Layer commits the transformation.

7) The pasted pic is added as a layer on top of the template layer. To see whether the cover pic is following the template guidelines, one needs to make one of these layers transparent.

Layer -> Stack -> Raise Layer/Lower Layer ... commands allows one to raise/lower layers.

I am not sure if this is the proper procedure but this has worked for me so far. Have pasted pic layer as the top layer. Then right-Click on pasted pic followed by choosing Layer -> Transparency -> Color to Alpha command. This brings up a dialog. On choosing OK in the dialog without making any changes, one will now see the template outline along with the pasted pic.

Right-Click on pic followed by Layer->Transparency->Remove Alpha Channel command removes the transparent behaviour and one gets back to earlier situation of pasted pic layer covering (obscuring) template layer below.

8) Save command saves the .xcf file.

9) To have only the cover image without the outer guidance lines and measurements, first make a copy of .xcf file. Open the copy .xcf file (in GIMP), and select only the cover image. Right click and choose Image -> Crop to Selection command.

10) Export As command creates jpg, pdf and other format output files. To have a pdf/jpg file output of cover pic, ensure that cover pic layer is in the foreground, using Layer -> Stack -> Raise Layer/Lower Layer ... commands. Ensure that transparancy is off and that the foreground layer has only the cover pic without outer measurement and other information. Now use Export As command. Don't change the default options in the Export dialog except for the output file format (jpg or pdf or ...).
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Additional useful stuff

A1) Sometimes in GIMP the DPI/PPI of a pic is shown as 100 when the same pic's DPI is shown as 300 in Paint. And the size of the pic is 3 times larger in GIMP than in Paint. To fix this issue in GIMP, choose Image->Scale Image command. Change the PPI (shown as 72 at times) to 300 for both X & Y resolution. In the dialog itself once you tab out of the PPI field with 300 value, the Width and Height fields value gets reduced appropriately. [In my particular case to 12.737 in. width x 9.25 in. height.] Press Scale in the dialog to make the changes.

A variation is when PPI is 100 but size in inches is correct (e.g. template PDF converted to image in GIMP). Changing PPI (x & y) to 300 reduces the width and height by 3. But if now the width and height are restored to previous values, the PPI does not change automatically. So the dialog will now have the original width & height and new 300 value for PPI (x & y). Press Scale in the dialog to make the changes.

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