- Part 1: Tesseract and Image Quality
- Part 2: Tesseract and Image Dimensions
- Part 3: Tesseract and Image Rotation (this post)
TLDR Summary
By far, image rotation has the greatest impact on the results of OCR using Tesseract. Images must be perfectly level for OCR to function.
Results
Anything more significant than ±2° introduces non-trivial errors into the text:
| rotation | image | Tesseract results |
|---|---|---|
| -10° |  |
Rights and freedons> an canade the canadian chartel of pights and freedoms guarantee> the rights and ‘greedons get out an it gubject onty to such Teasonadle Lanits presertbed by Law 2 can be Jenonstr ably justified tin a Free and genocratte society: gundanentat greedons everyone as the For lowing gundanentat greedons* (a) freedom Of conscience and religions (b) freedom of hough» petief> opinton and expresston” Ancudins freedo™ of the press and other medi? of anuncat tons () freedom Of peaceful assent? and @ ‘preedon OF mgsoct atten: pemocr atte rights of cutizens every catizen of canada aS the right *° yore 1 2% erection of members of the pouse of commons OF of & \egistatty® assembly and to De quartfted for member shtP herein |
| -5° |  |
Rights and freedoms an canada The Canadian Charter of Rights and Freedoms guarantees the rights and freedoms set out tn ‘it subject only to Such reasonable Limits prescribed by Law 25 can be demonstrably justified tn 2 free and denocratic soctety: Fundamental freedoms Everyone has the following fundamental freedoms: (a) freedom of conscience and religions (b) freedom of thought, belief, opinion and expression, including freedom of the press and other media of communicattons (c) freedom of peaceful assenblys and (a) freedom of association. pemocratic rights of citizens Every citizen of canada has the right to vote in an election of members oF the House of Connons or of & Legislative assembly and to be qualified for membership therein. |
| -3° |  |
Rights and freedoms in Canada the Canadian Charter of Rights and Freedoms guarantees The rights and freedoms set out tn it subject only to weep reasonable Lintts prescribed by lav 08 can be seconstrably justifted in a free and democratic soctety- Fundamental freedoms Everyone has the following fundamental freedoms: (a) freedom of conscience and religion; (b) freedom of thought, belief, opinion and expression, wed yuding Freedom of the press and ‘other media of communication; (c) freedom of peaceful assembly; and (d) freedom of assoctatton. pemocratic rights of citizens Every citizen of Canada has the right to vote in an election of menbers of the House of Connole or of a [egislative assembly and to be qualified for menbershtp therein. |
| -2° |  |
Rights and freedoms in Canada The Canadian Charter of Rights and Freedoms guarantees the rights and freedoms set out in it subject only to Such reasonable Limits prescribed by law as can be Jemonstrably justified in a free and democratic society. Fundamental freedoms Everyone has the following fundamental freedons: (a) freedom of conscience and religton; (b) freedom of thought, belief, opinion and expression, {netuding freedom of the press and other media of communication; (c) freedom of peaceful assembly; and (d) freedom of association. Democratic rights of citizens Every citizen of Canada has the right to vote in an Election of members of the House of Commons or of a legislative assembly and to be qualified for membership therein. |
| -1° |  |
Rights and freedoms in Canada The Canadian Charter of Rights and Freedoms guarantees the rights and freedoms set out in it subject only to such reasonable limits prescribed by law as can be demonstrably justified in a free and democratic society. Fundamental freedoms Everyone has the following fundamental freedoms: (a) freedom of conscience and religion; (b) freedom of thought, beltef, opinion and expression, including freedom of the press and other media of communication; (c) freedom of peaceful assembly; and (d) freedom of association. Democratic rights of citizens Every citizen of Canada has the right to vote in an election of members of the House of Commons or of a legislative assembly and to be qualified for membership therein. |
| 0° |  |
Rights and freedoms in Canada The Canadian Charter of Rights and Freedoms guarantees the rights and freedoms set out in it subject only to such reasonable limits prescribed by law as can be demonstrably justified in a free and democratic society. Fundamental freedoms Everyone has the following fundamental freedoms: (a) freedom of conscience and religion; (b) freedom of thought, belief, opinion and expression, including freedom of the press and other media of communication; (c) freedom of peaceful assembly; and (d) freedom of association. Democratic rights of citizens Every citizen of Canada has the right to vote in an election of members of the House of Commons or of a legislative assembly and to be qualified for membership therein. |
| +1° |  |
Rights and freedoms in Canada The Canadian Charter of Rights and Freedoms guarantees the rights and freedoms set out in it subject only to such reasonable Limits prescribed by law as can be demonstrably justified in a free and democratic society. Fundamental freedoms Everyone has the following fundamental freedoms: (a) freedom of conscience and religion; (b) freedom of thought, belief, opinion and expression, including freedom of the press and other media of communication; (c) freedom of peaceful assembly; and (d) freedom of association. Democratic rights of citizens Every citizen of Canada has the right to vote in an election of members of the House of Commons or of a legislative assembly and to be qualified for membership therein. |
| +2° |  |
Rights and freedoms in Canada The Canadian Charter of Rights and Freedoms guarantees the rights and freedoms set out in it subject only to such reasonable limits prescribed by law as can be demonstrably justified in a free and democratic society. Fundamental freedoms Everyone has the following fundamental freedoms: (a) freedom of conscience and religion; (b) freedom of thought, belief, opinion and expression, including freedom of the press and other media of communication; (c) freedom of Peaceful assembly; and (d) freedom of association. Democratic rights of citizens Every citizen of Canada has the right to vote in an election of members of the House of Commons or of a legislative assembly and to be qualified for membership therein. |
| +3° |  |
Rights and freedoms in canada The Canadian Charter of Rights and Freedoms guarantees the rights and freedoms set out in ic subject only to Such reasonable Limits prescribed by Law as can be demonstrably justified in a free and democratic society. Fundamental freedoms Everyone has the following fundamental freedoms: (a) freedom of conscience and religion; (b) Freedon of thought, better, opinion and expression, including freedom of the press’ and other media of communication; (c) freedom of peaceful assembly; and (d) Freedom of association. Democratic rights of citizens cLery Sitizen of canada has the right to vote in an election of menbers of the House of Commons or of a irgislative assenbly and to be quelifien for membership therein. |
| +5° |  |
Rights and freedoms in Canada The Canadian charter of Rights and Freedons guarantees the rights and freedoms set out in it subject only to such reasonable Limits prescribeq by law as can be demonstrably Justified in a free and democratic society, Fundamental freedoms Everyone has the following fundamental freedoms: (a) Freedom of conscience and religion; (b) Freedom of thought, belier, pinion and expression, including freedom of the press ‘and other media of communication; (c) freedom Of peaceful assembly; and (4) freedom of association, Democratic rights of citizens Every citizen OF Canada has the right to vote in an election of members of the House of Commons or of 3 legislative assembly and to be qualified for membership therein, |
| +10° |  |
Rights and Freedoms in Canada The Canadian Charter of Rights ang Freedoms Sarantees the rights and Freedoms Set out in it Subject only to Such Feasonable limits Prescribed bY Law 3s can be Seronstrapiy Justitieng i a Free and democratic Society, Fundanentay Freedoms Everyone has the Following Fundamentay Freedoms: (a) freedom of £nScience and "eligion; (b) Freedom oF thought. belie, Pinion and Pression, including Freedom of the press 2Nd othe, Media of Coyunication: (c) freedom of Peaceryy 2Ssembly, and (d) freedom oF *SSoctation. Pemocratic rights of Citizens Every Citizen of Canada has the right £0 vote in an lection of Menbers °F the House of Commons OF oF g legistative assembly 2d to be Walifieg for menbership therein, |
| +20° |  |
P*ighe, ang Peedon. th “enag, The adi an per te, or Ptohe. eng fom, Ce nteg, the “lone, ang Teedog. Seg Sut tn if nnbiec§ ony, to Such eesonagrt Limes inscribe by lay 85 cay be somone Jester ing Tree eng ema 2 Steg ener "reedon, “Mer yon has the owing oe eens. fay Free, of eas lencg eng tigte,. (by Cieetint oF uae Selig Pinion eng Stop nt Peeaop! oF the Pras. eng the, Medis or iC recat rte oF meee, mb, eng (ay "ecg oF Pesectae "menage. lone, of “Ehzen, very nitizey or “anag, has the Tigh, to rote 4, an ee tio oF enbene °F the House oF Corman OF op @ ets tae *Ssenpy eng to be Mate gem For “Mberspe, herein? |
| 180° |  |
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As you can see, I didn't bother marking up the HTML to highlight the differences with +20° or 180°. The results are so poor that it isn't worth the trouble.
To be effective, the text in the images must be rotated back to 0° before Tesseract can be used for OCR.
